JP7775006B2 - Observation optical system and observation device having the same - Google Patents

Description

The present invention relates to observation optical systems, and in particular to observation optical systems such as telescopes and binoculars, in which an image formed by an objective optical system is observed through an eyepiece optical system.

Observation optical systems such as those described above are expected to be small and lightweight, while still having a large aperture and high magnification.

The specifications of binoculars that use observation optical systems are determined by the aperture and magnification of the lens closest to the object in the binoculars' objective optical system; the larger the aperture, the heavier the binoculars. Magnification is also determined by the ratio of the focal length of the objective optical system to the focal length of the eyepiece optical system; to increase magnification, the focal length of the objective optical system must be lengthened or the focal length of the eyepiece optical system must be shortened, both of which result in larger and heavier binoculars. In other words, when attempting to achieve a large aperture and high magnification in binoculars, the bundle of rays passing through the objective optical system becomes larger, so the number of lenses required to correct aberrations such as spherical aberration and field curvature must be increased, the overall length of the objective optical system becomes longer, and the binoculars become larger.

In addition, the higher the magnification, the larger the image being observed, making hand shake more noticeable. Adding an anti-vibration function to address this makes the binoculars heavier. Therefore, if anti-vibration functions are added to binoculars with large apertures and high magnification, the binoculars will tend to become larger and heavier.

In addition, a prism vibration isolation mechanism that uses an image-inverting optical system (image-inverting prism) to isolate images is known as a mechanism capable of preventing significant hand shake in large-diameter, high-magnification binoculars. In this prism vibration isolation mechanism, an interpupillary distance adjustment prism for adjusting the left and right interpupillary distance is placed on the observation side of the image-inverting prism. This requires a long optical path length through three prisms: a roof prism, an auxiliary prism, and an interpupillary distance adjustment prism. In this prism vibration isolation mechanism, the optical path length of the three prisms is determined by the diameter of the light beam entering the image-inverting optical system. If the width of the light beam entering the image-inverting optical system is large, a corresponding optical path length is required through the prism, resulting in a heavier prism.

Therefore, in order to reduce the size and weight of an observation optical system equipped with a prism vibration isolation mechanism, it is necessary to reduce the size and weight of the prism in the image-inverting optical system by reducing the bundle of rays incident on the image-inverting optical system, or to use a configuration that reduces the weight of the lenses in the objective optical system.

Patent Document 1 discloses an observation device with an objective optical system with a focal length of approximately 180 mm. The objective optical system includes a lens element with positive refractive power, consisting of a cemented lens of a positive and a negative lens, located closest to the object; a next positive lens located a large distance away on the observation side of the lens element; and a cemented lens with strong negative refractive power located just before the object side of the image-inverting optical system. In this way, Patent Document 1 reduces the bundle of rays incident on the lens located closer to the observation side than the lens located closest to the object by providing the aforementioned spacing. This allows the lens diameter of the lens located closer to the observation side than the lens located closest to the object in the objective optical system to be reduced, enabling weight reduction. Furthermore, by placing a lens element with strong negative refractive power before the image-inverting optical system, the diameter of the image-inverting optical system is also reduced, resulting in a lighter weight.

Patent Document 2 discloses an observation device with an objective optical system with a focal length of approximately 150 mm to 180 mm. The objective optical system comprises a lens element with positive refractive power consisting of a cemented lens of a positive and negative lens placed closest to the object, a subsequent lens placed a large distance away on the observation side of the lens element, and a cemented lens with strong negative refractive power placed just before the object side of the image-inverting optical system. In Patent Document 2, by placing a lens element with strong negative refractive power before the image-inverting optical system, the diameter and weight of the image-inverting optical system are reduced.

Patent No. 4585638 Patent No. 6145514

However, with the observation optical system of Patent Document 1, if a structure is adopted in which the image inversion optical system is used as the vibration isolation mechanism, the spacing for arranging the interpupillary distance adjusting prism is insufficient, making it impossible to configure. Arranging the interpupillary distance adjusting prism would require increasing the overall size of the observation optical system, which is undesirable. Furthermore, the focal length of the objective optical system is short at 180 mm, and increasing the magnification to over 20x and increasing the aperture would result in an increase in the size of the observation device.

In addition, in Patent Document 2, a positive lens element is placed closest to the object side of the objective optical system, and the next lens is placed a large distance away on the observation side. However, the distance between the positive lens elements on the observation side is not large compared to the length from the object side of the objective optical system to the object side of the image-inverting optical system. This prevents the lens diameter of the lens on the observation side of the positive lens element from being small, making it difficult to reduce weight. Furthermore, in a structure in which the image-inverting optical system is used as an anti-vibration mechanism, there is insufficient space to place an interpupillary distance adjusting prism, making it impossible to construct such a structure. In order to place an interpupillary distance adjusting prism, the overall size of the observation optical system must be increased, which is undesirable. Furthermore, the focal length of the objective optical system is short at 180 mm, and if a high magnification of over 20x and a large aperture are used, the size of the observation device will increase.

The objective of the present invention is to provide an observation optical system that has a large aperture and high magnification, yet is compact and lightweight even when equipped with an anti-vibration mechanism that moves the image-inverting optical system.

According to one aspect of the present invention, there is provided an observation optical system which has, arranged in this order from the object side to the observation side, an objective optical system, an image-inverting optical system, and an eyepiece optical system, and which magnifies and observes an image formed by the objective optical system using the eyepiece optical system, the objective optical system comprising, arranged in this order from the object side to the observation side, a first lens group and a first lens element having the strongest negative refractive power within the objective optical system, and the first lens group includes a second lens element having positive refractive power which is arranged closest to the object side in the objective optical system, wherein the focal length of the objective optical system is f0, the focal length of the first lens element is fn, the distance on the optical axis from the lens surface closest to the observation side of the second lens element to the object side lens surface of a lens which is arranged next to the second lens element to the second lens element is d1, the distance on the optical axis from the lens surface closest to the object side of the second lens element P to the surface closest to the object side of the image-inverting optical system is d0 , and the focal length of the eyepiece optical system is fe ,
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
15.0 < fо/fe < 40.0
The present invention is characterized in that the following conditional expression is satisfied:

Other objects and features of the present invention are described in the following embodiments.

The present invention makes it possible to provide an observation optical system that is large-diameter and high-magnification, yet is compact and lightweight even when equipped with an anti-vibration mechanism that moves the image-inverting optical system.

FIG. 2 is a cross-sectional view of a lens of the observation optical system of Example 1. 3A to 3C are aberration diagrams of the observation optical system of Example 1. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a second embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 2. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a third embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 3. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a fourth embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 4. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a fifth embodiment. 10A to 10C are aberration diagrams of the observation optical system of Example 5. FIG. 10 is a cross-sectional view of a lens of an observation optical system according to a sixth embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 6. FIG. 13 is a cross-sectional view of a lens of an observation optical system according to a seventh embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 7. FIG. 13 is a cross-sectional view of a lens of an observation optical system according to an eighth embodiment. 13A to 13C are aberration diagrams of the observation optical system of Example 8. FIG. 1 is an explanatory diagram showing a binocular configuration. FIG. 2 is an explanatory diagram of an image-inverting optical system and a prism for adjusting an eye distance.

The following describes the observation optical systems and observation devices incorporating the optical systems according to each embodiment, with reference to the accompanying drawings.

Figures 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views of the lenses of the observation optical systems of Examples 1, 2, 3, 4, 5, 6, 7, and 8, respectively.

Figures 2, 4, 6, 8, 10, 12, 14, and 16 are afocal aberration diagrams of the observation optical systems of Examples 1, 2, 3, 4, 5, 6, 7, and 8, respectively.

The observation optical system in Example 1 has an aperture of φ50.1 mm and a magnification of 25.0x.

The observation optical system in Example 2 has an aperture of φ50.9 mm and a magnification of 25.0x.

The observation optical system in Example 3 has an aperture of φ50.8 mm and a magnification of 30.0x.

The observation optical system in Example 4 has an aperture of φ50.1 mm and a magnification of 21.0x.

The observation optical system in Example 5 has an aperture of φ50.1 mm and a magnification of 30.0x.

The observation optical system in Example 6 has an aperture of φ50.9 mm and a magnification of 25.0x.

The observation optical system in Example 7 has an aperture of φ50.9 mm and a magnification of 30.0x.

The observation optical system in Example 8 has an aperture of φ50.4 mm and a magnification of 30.0x.

The observation optical system in each embodiment has a prism vibration reduction function that reduces camera shake by moving the image inversion optical system (prism).

In each lens cross-sectional view, the left is the object side (front) and the right is the observation side (rear). The observation optical system in each embodiment is composed of an objective optical system o, an image-inverting optical system z, an eye-distance adjusting prism m, and an eyepiece optical system e, arranged in that order from the object side to the observation side.

In each embodiment, L1 is the first lens group, and lens element N (first lens element) is the lens element with the strongest negative refractive power (optical power = the reciprocal of the focal length) in the objective optical system o. Here, the lens group may be composed of a single lens or multiple lenses. The lens element refers to a single lens or a cemented lens composed of multiple lenses, and does not include a lens group composed of multiple lenses with an air gap between them. Furthermore, an intermediate image (first image plane) is formed within the eyepiece optical system e. EP is the pupil position.

The spherical aberration diagram shows the amount of spherical aberration for the d-line (wavelength 587.6 nm), g-line (wavelength 435.8 nm), F-line (486.1 nm), and C-line (656.3 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. The distortion diagram shows the amount of distortion for the d-line. The chromatic aberration diagram shows the amounts of chromatic aberration for the g-line, F-line, and C-line. ω is the half angle of view (°).

Using Figure 17, we will explain binoculars as an observation device 100 with prism vibration isolation. Figure 17 shows an observation device 100 equipped with a pair of left and right observation optical systems. In Figure 17, the upper side is the object side and the lower side is the observation side. The left observation optical system (first observation optical system) 100A is composed of, arranged from the object side to the observation side, an objective optical system o1, an image-inverting optical system z1 (auxiliary prism h1, roof prism dp1), an interpupillary distance adjusting prism m1, and an eyepiece optical system e1. The right observation optical system 100B is composed of, arranged from the object side to the observation side, an objective optical system o2, an image-inverting optical system z2 (auxiliary prism h2, roof prism dp2), an interpupillary distance adjusting prism m2, and an eyepiece optical system e2. The left observation optical system 100A is for the left eye, and the right observation optical system 100B is for the right eye. The observation optical systems 100A and 100B are arranged in parallel. The objective optical systems o1 and o2, the image-inverting optical systems z1 and z2, the interpupillary distance adjusting prisms m1 and m2, and the eyepiece optical systems e1 and e2 are all identical. The observation optical systems 100A and 100B are configured to be identical for the left and right eyes. k1 and k2 indicate the optical paths of light rays passing through the left and right eyes, respectively. Light rays k1 and k2 travel from the object side (upper) toward the observation side (lower), and enter the left and right eyes after passing through the eyepiece optical systems e1 and e2. This allows observation. Light rays k1 and k2 are reflected within the image-inverting optical systems z1 and z2. As a result, light rays k1 and k2 are inverted 180 degrees, and when the subject image is observed through the eyepiece optical systems e1 and e2, the subject image is observed as an erect image. Furthermore, because the light rays k1 and k2 are reflected within the eye distance adjustment prisms m1 and m2, the light ray spacing B between the eyepiece optical systems e1 and e2 becomes wider than the light ray spacing A between the objective optical systems o1 and o2.

Figure 18 shows the details of the optical path of ray k from the image-inverting optical system z to the interpupillary distance adjustment prism m. The left side is the object side. Ray k passes through the image-inverting optical system z (auxiliary prism h, roof prism dp) and the interpupillary distance adjustment prism m, and proceeds to the observation side. The interpupillary distance can be adjusted by rotating the interpupillary distance adjustment prism m in a direction perpendicular to the axis of ray k, as indicated by arrow y in the figure, relative to the axis of the light entering the interpupillary distance adjustment prism m.

Returning to Figure 17, we will now explain the prism vibration-proof structure. Image-inverting prism unit b (vibration prevention unit b), which is composed of a pair of left and right image-inverting optical systems z1 and z2, is moved parallel and/or tilted to correct camera shake. The parallel and/or tilted eccentric movement of vibration prevention unit b is performed by an actuator or similar. The lighter the vibration prevention unit b, the smaller the actuator can be, allowing for a lighter vibration prevention unit b. Furthermore, to reduce the weight of the mechanical components that hold the image-inverting optical systems z1 and z2, the image-inverting optical systems z1 and z2 are positioned closely together. Positioning the image-inverting optical systems z1 and z2 closely together results in the distance A between the objective optical systems o1 and o2 being smaller than the interpupillary distance. This makes binocular observation difficult. Therefore, interpupillary distance-adjusting prisms m1 and m2 are used to make the distance B between the eyepiece optical systems e1 and e2 wider than the distance A between the objective optical systems o1 and o2. Interpupillary distance adjustment can be achieved by rotating the interpupillary distance adjusting prism m in a direction perpendicular to the light ray k, as shown by arrow y in Figure 18. The objective optical systems o1, o2 and image-inverting optical systems z1, z2 can be integrated into an integrated structure E, the interpupillary distance adjusting prism m1 and eyepiece optical system e1 can be integrated into an integrated eyepiece unit D1, and the interpupillary distance adjusting prism m2 and eyepiece optical system e2 can be integrated into an integrated eyepiece lens unit D2, thereby making it possible to reduce the size of the observation device 100. Therefore, when using an anti-vibration mechanism that moves the left and right image-inverting optical systems z1, z2 as a single unit, a prism anti-vibration structure is required from the image-inverting optical systems z1, z2 to the interpupillary distance adjusting prisms m1, m2.

Figures 1 (Example 1), 3 (Example 2), 5 (Example 3), 7 (Example 4), 9 (Example 5), 11 (Example 6), 13 (Example 7), and 15 (Example 8) are cross-sectional views of the lenses of the observation optical system when the optical path length of the eye-distance adjusting prism m is converted into a straight line. Here, the optical path length refers to the length of the optical path traveled by a light ray within the image-inverting optical system z (prism, etc.).

As mentioned above, in Figures 1, 3, 5, 7, 9, 11, 13, and 15, if the distance L from the object side of the objective optical system o to the image side of the eyepiece optical system e can be shortened within the structural constraints of the vibration-proof structure from the image-inverting optical system z to the interpupillary distance adjustment prism m, the observation device 100 can be made more compact. If the image-inverting optical systems z1 and z2 are used as vibration-proof mechanisms, the optical path length required from the image-inverting optical systems z1 and z2 to the interpupillary distance adjustment prisms m1 and m2 is increased. Therefore, if the prisms of the image-inverting optical systems z1 and z2 can be made smaller, or if the lens configuration of the objective optical systems o1 and o2 can be constructed using lenses with smaller diameters, the observation device 100 can be made more compact and lightweight. Here, when increasing the aperture, the diameter of the lens closest to the object in the objective optical systems o1 and o2 is determined by the specifications of the large aperture and becomes larger. Furthermore, when increasing the magnification, the focal length of the objective optical systems o1 and o2 becomes longer, and the objective optical systems o1 and o2 become larger in the overall length direction.

In Figure 17, the objective optical systems o1 and o2 to the image-inverting optical systems z1 and z2 are integrated into an integrated structure E. Therefore, if the objective optical systems o1 and o2 become larger due to larger diameters and higher magnifications, the mechanical holding components will become larger and the integrated structure E will also become larger. In the objective optical systems o1 and o2, the outer diameter of the lens element closest to the object is determined by the lens specifications. In the objective optical systems o1 and o2, a lens element P with positive refractive power is placed closest to the object, and by leaving a gap between this and the lens placed next to lens element P on the observation side, the next lens can be placed at the position of the ray bundle converged by the positive refractive power of lens element P. This allows the outer diameter of the lens placed closer to the observation side to be smaller than the lens element P closest to the object in the objective optical systems o1 and o2.

Furthermore, by providing a gap between the lens element P and the lens located next to the observation side, and placing a lens element N with strong negative refractive power, the ray bundle on the object side of the image-inverting optical systems z1 and z2 can be reduced, thereby increasing the optical path length within the prism. This allows the image-inverting optical systems z1 and z2 to be made smaller and lighter. In other words, in each lens cross-sectional view, by placing the lens element P with positive refractive power closest to the object side of the objective optical systems o1 and o2 and increasing the ratio of the distance d1 to the distance d0, the lens diameter of the lens located closer to the observation side than the lens element P can be reduced. As a result, the overall weight of the objective optical systems o1 and o2 can be reduced. Here, the distance d0 is the distance from the object side of the objective optical systems o1 and o2 to the object side of the image-inverting optical systems z1 and z2. The distance d1 is the distance from the observation side of the lens element P with positive refractive power located closest to the object side of the objective optical systems o1 and o2 to the object side of the lens located next to the observation side.

Furthermore, by positioning the lens element N with the strongest negative refractive power in the objective optical systems o1 and o2 closer to the observation side, the diameter of the light beam entering the image-inverting optical systems z1 and z2 can be reduced, and the optical path length required to pass through the prisms of the image-inverting optical systems z1 and z2 can be increased. This reduces the diameter of the image-inverting optical systems z1 and z2, making it possible to reduce their weight.

The above configuration makes it possible to reduce the weight of the integrated structure E, from the objective optical systems o1 and o2 to the image-inverting optical systems z1 and z2. In order to make the objective optical system o and the image-inverting optical system z compact and lightweight with a large aperture and high magnification, the objective optical system o has a lens element P with positive refractive power that is located closest to the object, and a lens element N with the strongest negative refractive power within the objective optical system o that is located closer to the observation side.

The objective optical system о in Examples 1 to 6 is composed of, arranged in order from the object side to the observation side, a lens element P (second lens element) with positive refractive power, a lens group P2 (partial group) with positive refractive power, and a lens element N (first lens element) with the strongest negative refractive power within the objective optical system о. The lens element P and lens group P2 form a first lens group L1. The lens element P is composed of a single lens 11 (first lens) with positive refractive power. The lens group P2 is composed of a cemented lens of a lens 12 (second lens) with positive refractive power and a lens 13 (third lens) with negative refractive power, and a lens 14 (fourth lens) with positive refractive power. The lens element N with negative refractive power is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power.

The objective optical system о of Example 7 is composed of, arranged in order from the object side to the observation side, a lens element P with positive refractive power, a lens group P2 with positive refractive power, a lens element N with the strongest negative refractive power in the objective optical system о, and a single lens with positive refractive power. Lens element P and lens group P2 form a first lens group L1. Lens element P is composed of a single lens 11 (first lens) with positive refractive power. Lens group P2 is composed of a cemented lens of a lens 12 (second lens) with positive refractive power and a lens 13 (third lens) with negative refractive power, and a lens 14 (fourth lens) with positive refractive power. Lens element N is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power.

The objective optical system о of Example 8 is composed of, arranged in order from the object side to the observation side, a lens element P with positive refractive power, a lens group P2 with positive refractive power, a lens element N with the strongest negative refractive power in the objective optical system о, and a single lens with positive refractive power. Lens element P and lens group P2 form a first lens group L1. Lens element P is composed of a cemented lens 11 (first lens) consisting of a lens with positive refractive power and a lens with negative refractive power. Lens group P2 is composed of a cemented lens consisting of a lens 12 (second lens) with positive refractive power and a lens 13 (third lens) with negative refractive power, and a lens 14 (fourth lens) with positive refractive power. Lens element N is composed of a cemented lens consisting of a lens with positive refractive power and a lens with negative refractive power.

In order to guide the large bundle of rays from the objective optical system о to the small aperture of the image-inverting optical system z, the bundle of rays is converged by a lens element P with strong positive refractive power. Then, in order to pass the converged bundle of rays from the image-inverting optical system z to the eye-distance adjusting prism m, a lens element N with strong negative refractive power is placed on the observation side of the objective optical system о. Since the focal length of the objective optical system о increases to achieve higher magnification, the objective optical system о is designed to have a long focal length relative to its overall length, resulting in a large telephoto ratio.

In addition, by converging the light beam using lens element P, which has a strong positive refractive power, and by arranging lens group P2 at a distance from lens element P, the outer diameter of lens group P2 can be reduced. This makes it possible to reduce the weight of lenses in the objective optical system о that are arranged closer to the observation side than lens element P.

Furthermore, by positioning lens group P2 at a distance from lens element P, image-inverting optical system z can also be positioned at a distance from lens element P. This allows image-inverting optical system z to be positioned in a location where the light beam is small, and the outer diameter of image-inverting optical system z can be reduced, making it possible to reduce its weight.

In each embodiment, the first lens 11 and second lens 12 of the objective optical system are made of a glass material with anomalous dispersion to correct the secondary spectrum of axial chromatic aberration to accommodate high magnification specifications. To accommodate high magnification specifications, the focal length of the objective optical system о can be increased, but the longer the focal length of the objective optical system о, the worse the axial chromatic aberration becomes. Therefore, by using a glass material with high anomalous dispersion for the first lens 11, which is closest to the object and bends the large light beam entering the objective optical system о, and the second lens 12, which is located next to it, it is possible to correct the secondary spectrum of axial chromatic aberration.

In each embodiment, focusing from infinity to close range is achieved by moving the first lens unit L1 toward the object side as shown by the arrow in the figure, or by moving the lens element N toward the observation side as shown by the arrow in the figure.

In each embodiment, diopter adjustment can be performed by moving the first lens group L1, by moving the lens element N, or by moving the entire eyepiece optical system e.

Next, we will describe the characteristic configuration of the observation optical system in each embodiment.

The observation optical system in each embodiment has a large aperture and high magnification, but also has a prism vibration isolation mechanism that moves the image-inverting optical system z to provide vibration isolation, allowing for compactness and lightweight design.

The observation optical system in each embodiment has, arranged in order from the object side to the observation side, an objective optical system o, an image-inverting optical system z, and an eyepiece optical system e, and is an observation optical system for magnifying and observing an image formed by the objective optical system o using the eyepiece optical system e. The objective optical system o has, arranged in order from the object side to the observation side, a first lens group L1 and a lens element N with the strongest negative refractive power in the objective optical system o. The first lens group L1 includes a lens element P with positive refractive power that is arranged closest to the object side in the objective optical system o.

The observation optical system of each embodiment satisfies the following conditional expressions (1) and (2).

-15.00 < fо/fn < -3.00 ... (1)
0.35 < d1/dо < 0.90...(2)
Here, f0 is the focal length of objective optical system o, and fn is the focal length of lens element N. d1 is the distance on the optical axis from the lens surface of lens element P closest to the observation side to the object side lens surface of the lens located next to lens element P on the observation side. d0 is the distance on the optical axis from the lens surface of lens element P closest to the object side to the surface of image-inverting optical system z closest to the object side.

Conditional expression (1) defines the ratio between the focal length f o of objective optical system o and the focal length f n of lens element N, which has the strongest negative refractive power within objective optical system o. Exceeding the upper limit of conditional expression (1) makes the focal length of lens element N too long, making it difficult to reduce the beam of light incident on image-inverting optical system z. This results in a larger image-inverting optical system z. Increasing the aperture diameter of the entrance surface of image-inverting optical system z requires an optical path length proportional to the aperture size of the image-inverting optical system z, making the image-inverting optical system z larger and heavier. This, in turn, increases the size of the actuator for the vibration isolation mechanism and the weight of the observation optical system. Falling below the lower limit of conditional expression (1), makes the focal length of lens element N too short, reducing the beam of light incident on image-inverting optical system z. This is advantageous for making the image-inverting optical system z smaller and lighter, but a shorter negative focal length increases the field curvature of the observation optical system toward the overside, making correction difficult.

Conditional expression (2) defines the ratio of the distance d1 from the lens surface of lens element P closest to the observation side to the object-side lens surface of the lens located next to lens element P to the distance dо from the lens surface of lens element P closest to the observation side to the surface of image-inverting optical system z closest to the object side. Exceeding the upper limit of conditional expression (2) increases the distance from the lens surface of lens element P closest to the observation side to the object-side lens surface of the lens located next to lens element P. This allows the lens to be positioned where the diameter of the ray bundle converged by lens element P is small, allowing the lens diameter of the lens closer to the observation side than lens element P to be smaller. While this is advantageous for reducing the weight of objective optical system о, it requires a reduction in the number of lenses that can be placed due to space constraints, resulting in an insufficient number of lenses required to correct spherical aberration and field curvature. Alternatively, if the number of lenses is not reduced, objective optical system о would become very long and large, and the objective optical system о, including its mechanical mechanism, would become heavy. Furthermore, if the lower limit of conditional expression (2) is not reached, the distance from the lens surface of lens element P closest to the observation side to the object side lens surface of the lens positioned next to lens element P on the observation side becomes small. This requires the lens to be positioned before the diameter of the bundle of rays converged by lens element P becomes small, making it impossible to reduce the lens diameter of the lens closer to the observation side than lens element P, and therefore making it impossible to reduce the weight of the objective optical system o.

Furthermore, it is preferable that the numerical ranges of conditional expressions (1) and (2) satisfy the ranges of the following conditional expressions (1a) and (2a).

-12.00 < fо/fn < -3.20 ... (1a)
0.40 < d1/dо < 0.75...(2a)
It is more preferable that the numerical ranges of the conditional expressions (1) and (2) satisfy the ranges of the following conditional expressions (1b) and (2b).

-10.00 < fо/fn < -3.40 ... (1b)
0.42 < d1/dо < 0.60...(2b)
As described above, according to each embodiment, it is possible to realize an observation optical system that is small and lightweight, even though it has a large aperture and high magnification, and even if an anti-vibration mechanism that moves the image-inverting optical system z (prism) is installed.

Next, we will discuss the conditions that the observation optical system of each embodiment should preferably satisfy. The observation optical system of each embodiment should preferably satisfy one or more of the following conditional expressions.

0.60 < l/L < 0.90...(3)
-5.00 < fP/fn < -1.00 (4)
0.00 < fP/fP2 < 2.00 (5)
-2.00 < d1/fn < -0.30 (6)
-5.00 < f1/fn < -1.00 (7)
2.00 < fо/dо < 6.00...(8)
0.20 < f1/fо < 0.50 (9)
2.00 < φо/φp < 4.00 (10)
0.05 < np-nn < 0.35 (11)
1.00 < (nR1-nR2)/(nR1+nR2) < 5.00 (12)
0.02 < dn/dо < 0.15 (13)
15.00 < fо/fe < 40.00...(14)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (15)
60.0 < νd < 100.0 (16)
Here, L is the optical path length along the optical axis from the lens surface of the objective optical system o closest to the object to the lens surface of the eyepiece optical system e closest to the observation side. l is the optical path length along the optical axis from the surface of the image-inverting optical system z closest to the object to the lens surface of the eyepiece optical system e closest to the observation side. fP is the focal length of lens element P. fP2 is the focal length of lens group P2. f1 is the focal length of the first lens group L1. φo is the outer diameter of the lens of the objective optical system o closest to the object. φp is the outer diameter of the image-inverting optical system z closest to the object. np is the refractive index of the lens with positive refractive power that constitutes lens element N. nn is the refractive index of the lens with negative refractive power that constitutes lens element N. Lens element N is composed of a cemented lens of a lens with positive refractive power and a lens with negative refractive power. nR1 is the radius of curvature of the lens surface of lens element N closest to the object. nR2 is the radius of curvature of the lens surface of lens element N closest to the observation side. dn is the distance on the optical axis from the lens surface of lens element N closest to the observation side to the surface of image-inverting optical system z closest to the object side. fe is the focal length of eyepiece optical system e. θgF and νd are the partial dispersion ratio and Abbe number of the glass materials of first lens 11 and second lens 12, respectively. Conditional formula (3) defines the ratio of the optical path distance from the lens surface of objective optical system o closest to the object side to the lens surface of eyepiece optical system e closest to the observation side to the optical path distance from the surface of image-inverting optical system z closest to the object side to the lens surface of eyepiece optical system e closest to the observation side. If the distance from the surface of image-inverting optical system z closest to the object side to the lens surface of eyepiece optical system e becomes too large, exceeding the upper limit of conditional formula (3), the space available for arranging objective optical system o becomes too small, making it difficult to arrange an objective optical system o with a large aperture and high magnification. Furthermore, it becomes difficult to ensure the distance d1 on the observation side of the lens element P within the objective optical system o, making it impossible to reduce the lens diameter and weight, which is undesirable. Furthermore, if the lower limit of conditional expression (3) is exceeded, the distance from the surface closest to the object in the image-inverting optical system z to the lens surface closest to the observation side in the eyepiece optical system e becomes small. This allows for more space to be used in the objective optical system o, making it easier to ensure the distance d1 on the observation side of the lens element P and advantageous for reducing the weight of the objective optical system o. However, this is undesirable because it leaves no space for the interpupillary distance-adjusting prism m.

Conditional expression (4) defines the ratio between the focal length fP of the lens element P with positive refractive power that is located closest to the object in the objective optical system о and the focal length fn of the lens element N with the strongest negative refractive power in the objective optical system о. If the upper limit of conditional expression (4) is exceeded and the focal length of lens element P becomes shorter, this is advantageous for shortening the overall length of the objective optical system о, but it is undesirable because the focal length of lens element P becomes too short, resulting in large spherical aberration on the underside. Furthermore, if the focal length of lens element P becomes longer and falls below the lower limit of conditional expression (4), the overall length of the objective optical system о becomes too long, undesirably increasing the weight of the objective optical system о, including its mechanical components.

Conditional expression (5) defines the ratio between the focal length fP of the lens element P with positive refractive power that is located closest to the object in the objective optical system о and the focal length fP2 of the lens group P2. If the upper limit of conditional expression (5) is exceeded and the focal length of lens element P becomes longer, the focal length of lens group P2 must be shortened. If the focal length of lens element P becomes longer, the converging effect of lens element P weakens, preventing the outer diameter of lens group P2 from becoming smaller and making it difficult to reduce weight, which is undesirable. Furthermore, if the focal length of lens group P2 becomes shorter, the curvature of the lenses within lens group P2 must be increased, which is undesirable and makes it difficult to reduce weight. If the focal length of lens element P becomes shorter and falls below the lower limit of conditional expression (5), the converging effect of lens element P becomes greater, undesirably increasing spherical aberration and curvature of field on the underside.

Conditional expression (6) defines the ratio of the distance d1 from the lens surface of lens element P closest to the observation side to the object-side lens surface of the lens located next to lens element P closest to the observation side to the focal length fn of lens element N with the strongest negative refractive power in objective optical system о. If the upper limit of conditional expression (6) is exceeded and distance d1 becomes narrower, the lens diameter on the observation side of lens element P becomes larger, making it difficult to reduce the weight of the lens and the image-inverting optical system z, which is undesirable. If distance d1 becomes wider and falls below the lower limit of conditional expression (6), the lens diameter on the observation side of lens element P becomes smaller, which is advantageous for reducing weight, but the overall length of objective optical system о becomes larger, making it difficult to reduce the weight of objective optical system о, including its mechanical components, which is undesirable.

Conditional expression (7) defines the ratio between the focal length f1 of the first lens unit L1, which is located closer to the object than lens element N, and the focal length fn of lens element N. Exceeding the upper limit of conditional expression (7) makes the focal length of lens element N too large, necessitating a larger diameter for image-inverting optical system z, which undesirably increases the weight of the prism in image-inverting optical system z. Falling below the lower limit of conditional expression (7) makes the focal length of lens element N too small, allowing the diameter of image-inverting optical system z to be reduced, which is advantageous for weight reduction, but increases spherical aberration and curvature of field on the over side. Furthermore, the shorter focal length of lens element N increases the curvature of the lens, which undesirably increases the mass or requires an increased number of lenses.

Conditional expression (8) defines the ratio of the focal length f 0 of the objective optical system o to the distance d 0 from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z closest to the object. Exceeding the upper limit of conditional expression (8) is advantageous for achieving high magnification. However, the distance from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z closest to the object becomes too short, making it difficult to ensure the distance d1 on the observation side of the lens element P within the objective optical system o. As a result, it is not possible to reduce the lens diameter, making it difficult to achieve weight reduction, which is undesirable. Falling below the lower limit of conditional expression (8) makes it difficult to achieve high magnification. Furthermore, the distance from the lens surface of the objective optical system o closest to the object to the surface of the image-inverting optical system z becomes long, making it easier to ensure the distance d1 on the observation side of the lens element P, which is advantageous for weight reduction. However, this is undesirable because the overall length of the objective optical system o becomes too long, making it heavy, including the mechanical components of the objective optical system o.

Conditional expression (9) defines the ratio between the focal length f1 of the first lens unit L1, which is located closer to the object than the lens element N, and the focal length f0 of the objective optical system o. Exceeding the upper limit of conditional expression (9) is undesirable, as the focal length of the first lens unit L1 becomes longer, making the objective optical system o larger, or the focal length of the objective optical system o becomes too short, making it difficult to meet the magnification specifications. Falling below the lower limit of conditional expression (9) is undesirable, as the focal length of the objective optical system o becomes longer, which is advantageous for meeting high magnification specifications, but the focal length of the first lens unit L1 becomes too short, resulting in large spherical aberration and curvature of field on the underside.

Conditional formula (10) defines the ratio between the outer diameter φo of the lens closest to the object in the objective optical system o and the outer diameter φp of the lens closest to the object in the image-inverting optical system z. In each embodiment, the outer diameter is 1 mm larger than the effective diameter. If the upper limit of conditional formula (10) is exceeded, the diameter of the light beam entering the objective optical system o increases, and the light beam must be reduced to enter the image-inverting optical system z. This requires increasing the focal length of the first lens unit L1, which is located closer to the object than lens element N, and shortening the focal length of lens element N. This increases the curvature of the objective optical system o, undesirably increasing the weight of the lens. If the lower limit of conditional formula (10) is exceeded, the size of the image-inverting optical system z increases, making it heavy. This undesirably increases the size of the vibration-proofing mechanism.

Conditional expression (11) defines the difference between the refractive index np of the lens with positive refractive power and the refractive index nn of the lens with negative refractive power in lens element N, and is intended to improve correction of spherical aberration and curvature of field. Exceeding the upper limit of conditional expression (11) is undesirable because the spherical aberration and curvature of field will be over-corrected to the excessive extent, making it impossible to achieve good optical performance. Conversely, falling below the lower limit of conditional expression (11) is undesirable because the spherical aberration and curvature of field will be under-corrected, making it impossible to achieve good optical performance.

Conditional expression (12) defines the shape factor of lens element N. Exceeding the upper limit of conditional expression (12) is undesirable because the focal length of the air lens between lens element N and the object-side lens becomes short, spherical aberration and field curvature become undercorrected, and good optical performance cannot be obtained. Failing to exceed the lower limit of conditional expression (12) is undesirable because the focal length of the air lens between lens element N and the object-side lens becomes long, spherical aberration and field curvature become overcorrected, and good optical performance cannot be obtained.

Conditional expression (13) defines the ratio of the distance dn from the lens surface of lens element N closest to the observation side to the surface of image-inverting optical system z closest to the object side to the distance d0 from the lens surface of objective optical system o closest to the object side to the surface of image-inverting optical system z closest to the object side. Exceeding the upper limit of conditional expression (13) shortens the distance between lenses in objective optical system o, shortening the distance d1 between lens element P on the observation side. This makes it difficult to reduce the lens diameter of the lens located closer to the observation side than lens element P, which is undesirable. Falling below the lower limit of conditional expression (13) allows for more leeway in lens placement within objective optical system o, making it easier to ensure the distance d1 between lens element P on the observation side, and allowing for the lens diameter of the lens located closer to the observation side than lens element P, which is advantageous for reducing weight. It also facilitates correction of spherical aberration and curvature of field. However, it also increases the likelihood of interference between lens element N and image-inverting optical system z, which is undesirable.

Conditional expression (14) defines the ratio between the focal length f o of the objective optical system o and the focal length fe of the eyepiece optical system e, and also defines the magnification of the observation optical system. Exceeding the upper limit of conditional expression (14) increases the focal length of the objective optical system o, which is advantageous for high magnification specifications. However, increasing the focal length of the objective optical system o undesirably increases the overall length of the objective optical system o, leading to increased size and weight. Falling below the lower limit of conditional expression (14) is undesirable, as it will no longer be possible to achieve the specified high magnification.

Conditional expressions (15) and (16) define the partial dispersion ratio θgF and Abbe number νd of the first lens 11 and the second lens 12. Failing to satisfy conditional expression (15) is undesirable because it worsens the secondary spectrum of axial chromatic aberration. Satisfying conditional expression (15) while exceeding the upper limit of conditional expression (16) allows for good correction of the secondary spectrum of axial chromatic aberration, but no glass material exists. Satisfying conditional expression (15) while falling below the lower limit of conditional expression (16) allows for good correction of the secondary spectrum of axial chromatic aberration. However, this is undesirable because it reduces the difference in Abbe numbers between the second lens 12 and the third lens 13, making the radius of curvature of the cemented lens formed by the second lens 12 and the third lens 13 for chromatic aberration correction tight and increasing the lens weight.

Furthermore, it is preferable that the numerical ranges of conditional expressions (3) to (16) be within the ranges of the following conditional expressions (3a) to (16a).

0.63 < l/L < 0.80...(3a)
-4.00 < fP/fn < -1.20 ... (4a)
0.00 < fP/fP2 < 1.50...(5a)
-1.50 < d1/fn < -0.35 (6a)
-3.50 < f1/fn < -1.20 ... (7a)
2.30 < fо/dо < 5.00...(8a)
0.22 < f1/fо < 0.45 ... (9a)
2.20 < φо/φp < 3.50...(10a)
0.08 < np-nn < 0.30 (11a)
1.05 < (nR1-nR2)/(nR1+nR2) < 4.00...(12a)
0.03 < dn/dо < 0.14 ... (13a)
20.00 < fо/fe < 33.00...(14a)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (15a)
70.0 < νd < 90.0 (16a)
It is more preferable that the numerical ranges of the conditional expressions (3) to (16) be within the ranges of the following conditional expressions (3b) to (16b).

0.65 < l/L < 0.76...(3b)
-3.50 < fP/fn < -1.40 (4b)
0.00 < fP/fP2 < 1.20...(5b)
-1.20 < d1/fn < -0.40 (6b)
-2.70 < f1/fn < -1.35 (7b)
2.60 < fо/dо < 4.50...(8b)
0.24 < f1/fо < 0.43 ... (9b)
2.40 < φо/φp < 3.30 ... (10b)
0.10 < np-nn < 0.25 (11b)
1.10 < (nR1-nR2)/(nR1+nR2) < 3.30 (12b)
0.05 < dn/dо < 0.13...(13b)
20.50 < fо/fe < 31.00...(14b)
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0 ... (15b)
80.0 < νd < 85.0 (16b)
In the observation optical system of each embodiment, by configuring each element as described above, it is possible to achieve a large aperture and high magnification, yet remain small and lightweight even when equipped with a prism-based vibration isolation mechanism, and to provide excellent correction for spherical aberration, field curvature, etc.

Next, we will explain the configurations that each component of the observation optical system in each embodiment should preferably satisfy.

In the objective optical system о, the lens element P is preferably composed of a single lens, or a cemented lens consisting of a lens with positive refractive power and a lens with negative refractive power. The lens element P is located closest to the object in the objective optical system о, and is therefore located at the position where the ray bundle is largest, but the more lenses there are, the heavier the objective optical system о becomes. Furthermore, as the magnification increases, the focal length of the objective optical system о becomes longer, so the surface precision of the lenses is more likely to affect performance, and the more lens surfaces there are, the greater the impact on performance due to manufacturing errors in the lens surfaces. Therefore, the fewer lens surfaces there are, the better.

Furthermore, lens group P2, which is located on the observation side of lens element P, is preferably composed of a total of three lenses: a cemented lens consisting of lens 12 with positive refractive power and lens 13 with negative refractive power, and lens 14 with positive refractive power. By giving lens group P2 positive refractive power, the refractive power of lens element P is weakened, and lens element P and lens group P2 can share the responsibility of correcting spherical aberration caused by a large ray bundle. By placing lens element P2 in a position where the ray bundle is small, it is possible to reduce weight even with only three lenses. Furthermore, by using a so-called triplet configuration with positive, negative, and positive refractive powers, spherical aberration and field curvature are effectively corrected.

By using glass materials with anomalous dispersion for the positive refractive power lenses of lens element P and lens group P2, the increase in axial chromatic aberration that accompanies longer focal lengths is suppressed. It is effective to use glass materials with anomalous dispersion for the positive refractive power lenses of the first lens 11 and second lens 12, which have large beam diameters in the objective optical system о.

Also, on the observation side of lens group P2 is located lens element N, which is a cemented lens of a positive refractive power lens and a negative refractive power lens and has the strongest negative refractive power within the objective optical system о. As the refractive power of a lens increases, larger aberrations occur, but by making lens element N a cemented lens with a difference in refractive power between the positive and negative lenses, the curvature of field that occurs at large apertures and high magnifications is corrected. Chromatic aberration is also corrected by making lens element N a cemented lens.

Focusing is also performed by moving the first lens unit L1 toward the object side or by moving lens element N toward the observation side.

Furthermore, it is preferable that the eyepiece optical system e be composed of a total of seven lenses, arranged in order from the object side: a lens with negative refractive power, a lens with positive refractive power, a cemented lens of negative and positive refractive power lenses, a lens with positive refractive power, and a cemented lens of negative and positive refractive power lenses. This results in a configuration that allows for good correction of chromatic aberration of magnification while providing a wide angle of view.

Below are numerical examples 1 to 8 corresponding to examples 1 to 8, respectively.

In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Furthermore, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd and partial dispersion ratio θgF of a certain material are given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (435.8 nm) of the Fraunhofer lines are Nd, NF, NC, and Ng, respectively:
νd=(Nd-1)/(NF-NC)
θgF=(Ng-NF)/(NF-NC)
It is expressed as:

In each numerical example, d, focal length (mm), and half angle of view ω (°) are all values when the observation optical system of each example is focused on an object at infinity. "Total lens length" is the distance on the optical axis from the frontmost lens surface (the lens surface closest to the object) of the optical system to the pupil plane. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens. In each numerical example, signs are negative toward the object side and positive toward the observation side. In addition, the outer diameter φо of the lens closest to the object in the objective optical system о and the outer diameter φp of the lens closest to the object in the image-inverting optical system z are set to values 1 mm larger than the effective diameter in each numerical example.

[Numerical Example 1]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 52.215 8.10 1.49700 81.5 50.10 0.5375
2 -2959.039 29.86 49.49
3 45.545 7.02 1.49700 81.5 31.53 0.5375
4 -54.521 1.85 1.77250 49.6 30.28
5 62.108 1.00 28.05
6 41.019 3.36 1.49700 81.5 27.43 0.5375
7 270.559 8.51 26.81
8 -131.659 2.71 1.78800 47.4 21.69
9 -32.528 1.00 1.63854 55.4 21.31
10 30.860 5.00 19.65
11 ∞ 78.47 1.65844 50.9 19.00
12 ∞ 17.50 19.00
13 ∞ 40.50 1.65844 50.9 19.00
14 ∞ 4.00 19.00
15 -12.588 1.00 1.71300 53.9 12.14
16 161.876 5.81 13.37
17 -10.658 2.97 1.67270 32.1 15.48
18 -9.760 7.13 17.11
19 124.605 1.30 1.84666 23.8 23.53
20 20.491 9.38 1.49700 81.5 24.57
21 -57.170 0.20 27.28
22 60.156 9.52 1.59282 68.6 30.64
23 -25.551 0.20 31.28
24 26.181 1.40 1.84666 23.8 26.71
25 12.300 14.36 1.80400 46.6 22.59
26 80.970 13.00 17.13
Hitomi ∞

Various data magnification 24.98
Objective angle of view: 1.06
Total length (to pupil) 275.15
Pupil φ2.00
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 261.19 63.41 -265.46 -157.41
2 11 ∞ 136.47 44.62 -44.62
3 15 10.45 66.27 16.07 -9.08

Single lens data lens Initial surface Focal length
1 1 103.33
2 3 51.12
3 4 -37.33
4 6 96.81
5 8 54.17
6 9 -24.65
7 11 0.00
8 13 0.00
9 15 -16.34
10 17 73.92
11 19 -29.13
12 20 31.62
13 22 31.56
14 24 -28.73
15 25 16.50

[Numerical Example 2]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 59.443 7.27 1.49700 81.5 50.86 0.5375
2 1037.228 47.65 50.23
3 45.293 5.90 1.49700 81.5 28.00 0.5375
4 -49.410 1.85 1.77250 49.6 27.10
5 54.550 1.00 25.42
6 38.654 3.53 1.49700 81.5 25.11 0.5375
7 -2574.827 9.40 24.60
8 -98.952 2.64 1.78800 47.4 19.68
9 -28.698 1.00 1.63854 55.4 19.38
10 39.354 5.24 18.27
11 ∞ 72.27 1.65844 50.9 17.50
12 ∞ 17.50 17.50
13 ∞ 40.50 1.65844 50.9 17.50
14 ∞ 4.00 17.50
15 -12.588 1.00 1.71300 53.9 12.65
16 -141.026 5.38 13.87
17 -10.646 2.68 1.67270 32.1 15.57
18 -9.760 9.36 16.97
19 -2168.096 1.30 1.84666 23.8 23.10
20 25.840 8.00 1.49700 81.5 24.30
21 -45.267 0.20 26.29
22 64.081 8.07 1.59282 68.6 28.90
23 -26.725 0.20 29.35
24 22.674 1.40 1.84666 23.8 25.48
25 11.377 12.65 1.80400 46.6 21.34
26 57.256 13.00 16.78
Hitomi ∞

Various data magnification 24.99
Objective angle of view: 1.06
Total length (to the eye) 283.00
Pupil φ2.03
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 273.87 80.24 -286.14 -173.24
2 11 ∞ 130.27 42.75 -42.75
3 15 10.95 63.24 16.89 -9.62

Single lens data lens Initial surface Focal length
1 1 126.56
2 3 48.55
3 4 -33.30
4 6 76.66
5 8 50.46
6 9 -25.84
7 11 0.00
8 13 0.00
9 15 -19.45
10 17 78.67
11 19 -30.15
12 20 34.38
13 22 32.90
14 24 -28.60
15 25 15.73

[Numerical Example 3]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 53.472 8.55 1.49700 81.5 50.82 0.5375
2 -2326.172 29.00 50.07
3 50.080 7.07 1.49700 81.5 32.34 0.5375
4 -55.600 1.85 1.77250 49.6 31.08
5 75.376 1.16 29.01
6 35.766 3.87 1.49700 81.5 28.05 0.5375
7 124.327 6.95 27.13
8 -461.121 2.94 1.78800 47.4 22.98
9 -38.408 1.00 1.63854 55.4 22.50
10 26.339 5.00 20.41
11 ∞ 81.87 1.65844 50.9 19.82
12 ∞ 17.50 19.82
13 ∞ 40.50 1.65844 50.9 19.82
14 ∞ 4.00 19.82
15 -12.588 1.00 1.71300 53.9 9.75
16 27.161 4.35 10.61
17 -13.151 5.35 1.67270 32.1 12.78
18 -9.760 5.58 15.85
19 55.191 1.30 1.84666 23.8 19.54
20 14.581 6.15 1.49700 81.5 19.74
21 81.114 0.20 21.49
22 38.461 8.15 1.59282 68.6 22.88
23 -19.223 0.20 23.70
24 32.668 1.40 1.84666 23.8 21.44
25 12.334 9.43 1.80400 46.6 19.26
26 -86.073 13.00 17.16
Hitomi ∞

Various data magnification 29.96
Objective angle of view: 0.89
Total length (to pupil) 267.38
Pupil φ1.69
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 254.08 62.40 -239.70 -148.92
2 11 ∞ 139.87 45.64 -45.64
3 15 8.47 56.11 13.40 -7.12

Single lens data lens Initial surface Focal length
1 1 105.30
2 3 54.22
3 4 -41.17
4 6 99.58
5 8 53.01
6 9 -24.32
7 11 0.00
8 13 0.00
9 15 -11.94
10 17 34.43
11 19 -23.75
12 20 34.70
13 22 22.82
14 24 -24.17
15 25 14.02

[Numerical Example 4]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 53.416 8.36 1.49700 81.5 50.10 0.5375
2 -4806.621 32.83 49.33
3 43.606 6.91 1.49700 81.5 30.15 0.5375
4 -55.974 1.85 1.78800 47.4 28.77
5 62.411 1.55 26.77
6 60.697 2.65 1.49700 81.5 26.25 0.5375
7 198.535 8.85 25.63
8 -89.485 2.33 1.75700 47.8 21.73
9 -36.121 1.00 1.53996 59.5 21.50
10 46.595 7.34 20.41
11 ∞ 79.16 1.65844 50.9 19.17
12 ∞ 17.50 19.17
13 ∞ 40.50 1.65844 50.9 19.17
14 ∞ 4.08 19.17
15 -12.588 1.00 1.71300 53.9 11.59
16 378.140 5.76 12.64
17 -10.643 2.42 1.67270 32.1 15.60
18 -9.760 2.00 16.28
19 51.099 1.30 1.84666 23.8 21.06
20 17.719 7.89 1.49700 81.5 21.55
21 -53.578 0.20 23.33
22 35.822 8.42 1.59282 68.6 26.00
23 -29.175 0.20 26.26
24 19.580 1.40 1.84666 23.8 22.78
25 10.700 11.32 1.80400 46.6 19.33
26 25.153 13.00 14.08
Hitomi ∞

Various data magnifications: 20.98
Objective angle of view: 1.24
Total length (to pupil) 269.82
Pupil φ2.39
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 247.82 66.33 -210.09 -144.89
2 11 ∞ 137.16 44.83 -44.83
3 15 11.80 54.91 13.56 -12.89

Single lens data lens Initial surface Focal length
1 1 106.36
2 3 50.48
3 4 -37.19
4 6 174.79
5 8 78.54
6 9 -37.52
7 11 0.00
8 13 0.00
9 15 -17.07
10 17 83.21
11 19 -32.62
12 20 27.81
13 22 28.50
14 24 -30.04
15 25 17.17

[Numerical Example 5]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 50.699 8.01 1.49700 81.5 50.10 0.5375
2 661.066 36.17 49.42
3 44.900 6.89 1.49700 81.5 29.70 0.5375
4 -43.375 1.85 1.77250 49.6 28.58
5 64.266 2.46 26.59
6 29.396 4.33 1.49700 81.5 25.41 0.5375
7 164.152 5.94 24.44
8 -290.334 3.71 1.78800 47.4 20.73
9 -27.915 1.00 1.63854 55.4 20.03
10 21.017 9.43 17.82
11 ∞ 68.42 1.65844 50.9 16.57
12 ∞ 17.50 16.57
13 ∞ 40.50 1.65844 50.9 16.57
14 ∞ 10.00 16.57
15 -12.588 1.00 1.71300 53.9 11.04
16 228.659 6.80 11.97
17 -11.499 2.90 1.67270 32.1 14.94
18 -9.760 7.91 16.31
19 34.514 1.30 1.84666 23.8 20.80
20 14.322 8.04 1.49700 81.5 20.43
21 -95.090 0.20 21.70
22 27.142 6.96 1.59282 68.6 23.43
23 -30.778 0.20 23.28
24 30.553 1.40 1.84666 23.8 20.42
25 12.366 7.08 1.80400 46.6 17.99
26 93.984 13.00 15.65
Hitomi ∞

Various data magnifications 30.00
Objective angle of view: 0.89
Total length (to the eye) 272.99
Pupil φ1.67
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 300.01 70.36 -375.85 -191.78
2 11 ∞ 126.42 41.59 -41.59
3 15 10.00 56.79 15.63 -9.21

Single lens data lens Initial surface Focal length
1 1 110.00
2 3 45.57
3 4 -33.27
4 6 71.29
5 8 38.95
6 9 -18.63
7 11 0.00
8 13 0.00
9 15 -16.71
10 17 57.44
11 19 -29.79
12 20 25.67
13 22 25.47
14 24 -25.44
15 25 17.05

[Numerical Example 6]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 60.874 7.68 1.49700 81.5 50.87 0.5375
2 -1926.022 44.17 50.23
3 43.979 6.29 1.49700 81.5 28.00 0.5375
4 -44.285 1.50 1.77250 49.6 27.00
5 56.759 1.00 25.36
6 28.718 4.31 1.49700 81.5 24.82 0.5375
7 2563.214 5.03 24.12
8 -230.615 3.26 1.78800 47.4 20.76
9 -32.806 1.00 1.63854 55.4 20.12
10 25.442 5.00 18.26
11 ∞ 64.75 1.65844 50.9 17.50
12 ∞ 10.30 17.50
13 ∞ 30.00 1.65844 50.9 17.50
14 ∞ 4.00 17.50
15 -12.588 1.00 1.71300 53.9 10.27
16 24.037 5.30 11.29
17 -13.001 3.87 1.67270 32.1 14.24
18 -9.760 5.34 16.26
19 -630.794 1.30 1.84666 23.8 22.05
20 23.598 11.08 1.49700 81.5 23.69
21 -22.137 0.20 26.60
22 86.767 8.31 1.59282 68.6 29.90
23 -25.418 0.20 30.30
24 33.904 1.40 1.84666 23.8 25.27
25 12.709 8.71 1.80400 46.6 21.65
26 172.007 15.00 19.65
Hitomi ∞

Various data magnification 24.98
Objective angle of view: 1.25
Total length (to the eye) 250.00
Pupil φ2.03
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 219.51 74.24 -212.64 -138.09
2 11 ∞ 105.05 33.72 -33.72
3 15 8.78 61.71 13.80 -7.42

Single lens data lens Initial surface Focal length
1 1 118.88
2 3 45.47
3 4 -32.00
4 6 58.40
5 8 48.19
6 9 -22.29
7 11 0.00
8 13 0.00
9 15 -11.46
10 17 39.32
11 19 -26.84
12 20 24.99
13 22 34.10
14 24 -24.76
15 25 16.66

[Numerical Example 7]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 50.680 7.80 1.49700 81.5 50.87 0.5375
2 496.736 38.04 50.24
3 38.662 7.30 1.49700 81.5 29.20 0.5375
4 -50.052 1.85 1.77250 49.6 27.70
5 60.630 1.98 25.65
6 38.023 3.01 1.49700 81.5 24.67 0.5375
7 103.992 9.92 23.89
8 -158.296 2.79 1.81600 46.6 18.54
9 -26.020 1.00 1.69350 50.8 18.17
10 25.600 2.00 16.78
11 30.460 2.00 1.43875 94.7 16.60
12 39.420 3.00 16.19
13 ∞ 65.35 1.65844 50.9 15.90
14 ∞ 17.50 15.90
15 ∞ 40.50 1.65844 50.9 15.90
16 ∞ 7.74 15.90
17 -12.588 1.00 1.71300 53.9 10.83
18 72.554 6.80 11.82
19 -11.388 2.90 1.67270 32.1 15.05
20 -9.760 6.32 16.48
21 38.148 1.30 1.84666 23.8 22.05
22 16.567 14.34 1.49700 81.5 21.95
23 -22.141 0.20 24.70
24 21.391 6.87 1.59282 68.6 24.73
25 -93.782 0.20 23.64
26 42.478 1.40 1.84666 23.8 21.21
27 12.366 6.89 1.80400 46.6 18.05
28 41.344 13.00 15.21
Hitomi ∞

Various data magnifications 30.00
Diagonal angle of view: 0.89
Total length (to the eye) 273.00
Pupil φ1.70
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 300.00 77.70 -413.23 -202.75
2 13 ∞ 123.35 40.66 -40.66
3 17 10.00 61.22 15.13 -9.93

Single lens data lens Initial surface Focal length
1 1 112.90
2 3 45.12
3 4 -35.24
4 6 118.80
5 8 37.80
6 9 -18.46
7 11 285.96
8 13 0.00
9 15 0.00
10 17 -14.97
11 19 59.14
12 21 -35.57
13 22 21.74
14 24 30.05
15 26 -21.05
16 27 19.84

[Numerical Example 8]
Unit: mm

Surface data Surface number rd nd νd Effective diameter θgF
1 50.515 10.05 1.49700 81.5 50.41 0.5375
2 -260.000 2.00 1.65160 58.5 49.57
3 -20090.372 33.03 48.51
4 38.401 7.32 1.49700 81.5 29.30 0.5375
5 -51.177 1.85 1.77250 49.6 27.74
6 62.380 2.67 25.63
7 42.806 2.86 1.49700 81.5 24.35 0.5375
8 119.571 10.00 23.56
9 -99.787 2.64 1.88300 40.8 18.04
10 -27.328 1.00 1.69350 50.8 17.68
11 24.960 2.00 16.40
12 25.513 2.00 1.43875 94.7 16.22
13 32.971 3.90 15.79
14 ∞ 63.19 1.65844 50.9 15.30
15 ∞ 17.50 15.30
16 ∞ 40.50 1.65844 50.9 15.30
17∞6.79 15.30
18 -12.588 1.00 1.71300 53.9 10.95
19 121.590 6.80 11.92
20 -10.840 2.90 1.67270 32.1 14.92
21 -9.760 6.76 16.51
22 38.217 1.30 1.84666 23.8 22.29
23 16.569 14.48 1.49700 81.5 22.18
24 -22.430 0.20 25.00
25 22.013 8.69 1.59282 68.6 25.16
26 -93.545 0.20 23.24
27 44.777 1.40 1.84666 23.8 21.02
28 12.933 6.83 1.80400 46.6 18.10
29 50.275 13.00 15.36
Hitomi ∞

Various data magnifications 30.00
Objective angle of view: 0.89
Total length (to pupil) 272.86
Pupil φ1.68
Eye relief 13.0
Viewing angle 2ω 52.0°

Zoom lens group data group Starting surface Focal length Lens length Front principal point position Rear principal point position
1 1 303.94 77.42 -441.40 -207.70
2 14 ∞ 121.19 40.01 -40.01
3 18 10.13 63.56 15.68 -10.30

Single lens data lens Initial surface Focal length
1 1 86.03
2 2 -404.27
3 4 45.37
4 5 -36.14
5 7 132.52
6 9 41.90
7 10 -18.66
8 12 237.64
9 14 0.00
10 16 0.00
11 18 -15.95
12 20 70.03
13 22 -35.53
14 23 21.87
15 25 30.92
16 27 -21.92
17 28 20.03

The various values in each numerical example are summarized in Table 1 below.

In the above embodiments, the present invention has been described as being applied to observation optical systems (types of optical systems that form an intermediate image within the optical system), such as binoculars and telescopes, but the present invention is not limited to observation optical systems. The present invention may also be applied to imaging optical systems that form a real image of a subject (object) on a photoelectric conversion element, i.e., optical devices such as digital still cameras, video cameras, interchangeable lenses that can be attached to camera bodies (such as single-lens reflex cameras), and mobile phone cameras. The above embodiments can be applied to a variety of optical systems that have imaging optical systems and observation optical systems.

The above describes preferred embodiments and examples of the present invention, but the present invention is not limited to these embodiments and examples, and various combinations, modifications, and variations are possible within the scope of the invention.

Objective optical system o, o1, o2
Image inversion optical system z, z1, z2
Eyepiece optical system e, e1, e2
First lens group L1
First lens element N
Second lens element P

Claims (35)

It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element to the observation side, d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side , and fe be the focal length of the eyepiece optical system .
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
15.0 < fо/fe < 40.0
An observation optical system characterized by satisfying the following conditional expression: Let L be the optical path length along the optical axis from the lens surface of the objective optical system closest to the object to the lens surface of the eyepiece optical system closest to the observation side, and l be the optical path length along the optical axis from the surface of the image-inverting optical system closest to the object to the lens surface of the eyepiece optical system closest to the observation side.
0.60 < l/L < 0.90
2. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the focal length of the second lens element is fP,
-5.00 < fP/fn < -1.00
3. The viewing optical system according to claim 1, wherein the following condition is satisfied: the first lens group further includes a subgroup disposed between the second lens element and the first lens element;
When the focal length of the second lens element is fP and the focal length of the subgroup is fP2,
0.00 < fP/fP2 < 2.00
4. The viewing optical system according to claim 1, wherein the following condition is satisfied: It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
the first lens group further includes a subgroup disposed between the second lens element and the first lens element;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element to the observation side, d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side, fP be the focal length of the second lens element, and fP2 be the focal length of the subgroup.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
0.00 < fP/fP2 < 2.00
An observation optical system characterized by satisfying the following conditional expression: -2.00 < d1/fn < -0.30
6. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the focal length of the first lens group is f1,
-5.00 < f1/fn < -1.00
7. The viewing optical system according to claim 1, wherein the following condition is satisfied: 2.00 < fо/dо < 6.00
8. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the focal length of the first lens group is f1,
0.20 < f1/fо < 0.50
9. The viewing optical system according to claim 1, wherein the following condition is satisfied: When the outer diameter of the lens closest to the object side of the objective optical system is φo and the outer diameter of the image-inverting optical system closest to the object side is φp,
2.00 < φо/φp < 4.00
10. The viewing optical system according to claim 1, wherein the following condition is satisfied: It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side, φ0 be the outer diameter of the lens closest to the object side of the objective optical system, and φp be the outer diameter of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
2.00 < φо/φp < 4.00
An observation optical system characterized by satisfying the following conditional expression: the first lens element is composed of a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power;
When the refractive index of the lens having the positive refractive power is np and the refractive index of the lens having the negative refractive power is nn,
0.05 < np-nn < 0.35
12. The viewing optical system according to claim 1, wherein the following condition is satisfied: It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
the first lens element is composed of a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power;
When the refractive index of the lens having the positive refractive power is np and the refractive index of the lens having the negative refractive power is nn,
When the focal length of the objective optical system is f0, the focal length of the first lens element is fn, the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element to the observation side is d1, the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side is d0, the refractive index of the lens with positive refractive power is np, and the refractive index of the lens with negative refractive power is nn,
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
0.05 < np-nn < 0.35
An observation optical system characterized by satisfying the following conditional expression: When the radius of curvature of the lens surface of the first lens element closest to the object side is nR1 and the radius of curvature of the lens surface of the first lens element closest to the observation side is nR2,
1.00 < (nR1-nR2)/(nR1+nR2) < 5.00
14. The viewing optical system according to claim 1, wherein the following condition is satisfied: 1.0 < 1.0 <1.0. It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
When the radius of curvature of the lens surface of the first lens element closest to the object side is nR1 and the radius of curvature of the lens surface of the first lens element closest to the observation side is nR2,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, and d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
1.00 < (nR1-nR2)/(nR1+nR2) < 5.00
An observation optical system characterized by satisfying the following conditional expression: When the distance on the optical axis from the lens surface of the first lens element closest to the observation side to the surface of the image-inverting optical system closest to the object side is dn,
0.02 < dn/dо < 0.15
16. The viewing optical system according to claim 1, wherein the following condition is satisfied: It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element to the observation side, d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object, and dn be the distance on the optical axis from the lens surface of the first lens element closest to the observation side to the surface of the image-inverting optical system closest to the object.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
0.02 < dn/dо < 0.15
An observation optical system characterized by satisfying the following conditional expression: 18. The observation optical system according to claim 1, wherein the first lens element moves toward the observation side during focusing. 19. The observation optical system according to claim 1, wherein the first lens group moves toward the object side during focusing. 20. The observation optical system according to claim 1, wherein vibration reduction due to camera shake is performed by moving the image-inverting optical system parallel to the axis or tilting the axis. 21. The observation optical system according to claim 1, wherein the first lens group includes, as the second lens element, a first lens having positive refractive power, a cemented lens of a second lens having positive refractive power and a third lens having negative refractive power, arranged in this order from the object side to the observation side. It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
the first lens group includes, as the second lens element, a first lens having positive refractive power, a cemented lens of a second lens having positive refractive power and a third lens having negative refractive power, which are arranged in this order from the object side to the observation side,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, and d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
An observation optical system characterized by satisfying the following conditional expression: When the Abbe number of the glass material of the first lens having a positive refractive power and the second lens having a positive refractive power is νd and the partial dispersion ratio is θgF,
θgF-(-1.665×10 ^-7・νd ³ +5.213×10 ⁻⁵・νd ² −5.656×10 ⁻³・νd+0.737)> 0
60.0 < νd < 100.0
23. The viewing optical system according to claim 21, wherein the following condition is satisfied: 24. The viewing optical system according to claim 1, wherein the second lens element is composed of one single lens or a cemented lens made up of a lens with positive refractive power and a lens with negative refractive power. The observation optical system according to claim 4, characterized in that the subgroup is composed of three lenses, arranged in order from the object side to the observation side: a cemented lens consisting of a lens with positive refractive power and a lens with negative refractive power, and a lens with positive refractive power. 25. The observation optical system according to claim 1, wherein the objective optical system is composed of the first lens group and the first lens element, arranged in this order from the object side to the observation side. It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system is composed of, in order from the object side to the observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system,
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, and d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
An observation optical system characterized by satisfying the following conditional expression: 27. The observation optical system according to claim 1, wherein the objective optical system is composed of, in order from the object side to the observation side, the first lens group, the first lens element, and a single lens with positive refractive power. 20. The observation optical system according to claim 1, wherein the first lens group is composed of, arranged in order from the object side to the observation side, the second lens element, a cemented lens of a lens with positive refractive power and a lens with negative refractive power, and a lens with positive refractive power. It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
the first lens group is composed of, arranged in order from the object side to the observation side, the second lens element, a cemented lens of a lens having positive refractive power and a lens having negative refractive power, and a lens having positive refractive power;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, and d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
An observation optical system characterized by satisfying the following conditional expression: 31. The observation optical system according to claim 1, wherein the eyepiece optical system is composed of a total of seven lenses, arranged in order from the object side to the observation side: a lens with negative refractive power, a lens with positive refractive power, a cemented lens of a lens with negative refractive power and a lens with positive refractive power, a lens with positive refractive power, and a cemented lens of negative refractive power and a lens with positive refractive power. It has an objective optical system, an image inversion optical system, and an eyepiece optical system, which are arranged in this order from the object side to the observation side,
An observation optical system in which an image formed by the objective optical system is magnified and observed by the eyepiece optical system,
the objective optical system includes, arranged in order from an object side to an observation side, a first lens group and a first lens element having the strongest negative refractive power in the objective optical system;
the first lens group includes a second lens element having a positive refractive power and arranged closest to the object in the objective optical system,
The eyepiece optical system is composed of seven lenses, arranged in this order from the object side to the observation side: a lens with negative refractive power, a lens with positive refractive power, a cemented lens of a lens with negative refractive power and a lens with positive refractive power, a lens with positive refractive power, and a cemented lens of negative refractive power and a lens with positive refractive power;
Let f0 be the focal length of the objective optical system, fn be the focal length of the first lens element, d1 be the distance on the optical axis from the lens surface of the second lens element closest to the observation side to the object side lens surface of the lens arranged next to the second lens element closest to the observation side, and d0 be the distance on the optical axis from the lens surface of the second lens element closest to the object side to the surface of the image-inverting optical system closest to the object side.
-15.00 < fо/fn < -3.00
0.35 < d1/dо < 0.90
An observation optical system characterized by satisfying the following conditional expression: 33. The observation optical system according to claim 1, wherein the observation optical system comprises, in order from the object side to the observation side, the objective optical system, the image-inverting optical system, an eye- distance adjusting prism, and the eyepiece optical system. 34. An observation device comprising two observation optical systems, namely, a first observation optical system as the observation optical system according to any one of claims 1 to 33 and a second observation optical system as the observation optical system. 35. The observation device according to claim 34 , wherein the two observation optical systems are arranged in parallel.