JP3375446B2 - Compound optical system for camera - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite optical system for a camera which separates subject light incident through a first optical system and guides it to a second optical system. The present invention relates to a compound optical system for a camera that guides the generated light flux to an observation optical system and enables photographing and observation of a subject.

[0002]

2. Description of the Related Art Conventionally, as a composite optical system for a camera of this type, an optical system combining a film photographic optical system and a naked-eye viewfinder optical system such as a single-lens reflex camera, or a photographing optical system is used. An optical system that separates the optical path for electrophotography by arranging a beam splitter on the film side, and arranges an image sensor such as CCD at a position conjugate with the film surface to enable both filming and electrophotography. The system etc. are known.

The observation optical system separated from the photographing optical system is provided with a condenser lens at a position conjugate with the image plane, and the condenser lens is used for the exit pupil of the photographing optical system and the finder optical system or for electrophotography. Is set to match the entrance pupil of the re-imaging optical system.

[0004]

However, in the above-described conventional compound optical system for a camera, since the position and focal length of the condenser lens are fixed, the exit pupil position of the photographing optical system changes due to lens replacement or zooming. In such a case, the matching of the pupil is not good, and the luminous flux incident on the entrance pupil causes vignetting, which causes a problem that the peripheral light amount of the image sensor or the finder becomes insufficient.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. Even when the exit pupil position of the photographing optical system is changed, the exit pupil and the entrance pupil of the observation optical system are It is an object of the present invention to provide a compound optical system for a camera, which is capable of excellent matching.

[0006]

In order to achieve the above-mentioned object, a compound optical system for a camera according to the present invention comprises a first optical system for forming a subject image on an image pickup surface and a first optical system. A composite optical system for a camera, comprising: an optical path separating unit that separates a light beam incident via the optical path toward an imaging surface; and a second optical system that guides a light beam from a subject separated by the optical path separating unit. Disposing a condenser lens composed of at least two independent lenses in the optical system, and moving at least one lens of the condenser lens in the optical axis direction according to the position of the exit pupil of the first optical system. Is characterized in that the distance between the lenses is relatively changed.

[0007]

Embodiments of the composite optical system for a camera according to the present invention will be described below. The embodiment shows an example in which the present invention is applied to a camera of a type in which an optical system for film photography as a first optical system and an optical system for electrophotography as a second optical system are provided side by side.

As shown in FIG. 1 (A), a light beam incident from the subject side, which is the left side in the figure, is imaged by a photographing optical system 1 on a film 2 which is an image pickup surface. A mirror 3 as an optical path separating means for separating an optical path is arranged between the photographing optical system 1 and the film 2, and a condenser lens 4, a mirror 5, a relay lens system 6 are provided in the optical path separated by the mirror 3. An observation optical system including the image pickup device 7 is arranged.

In this example, the photographing optical system 1 is a zoom lens composed of a first lens group 1a having a negative power and a second lens group 1b having a positive power. As shown in B, each group moves in the optical axis direction to change the image magnification.

The mirror 3 is a quick return mirror or a half mirror, and guides a light beam to the observation optical system at least when the film 2 is not photographed except when photographing. The condenser lens 4 is at least two lenses,
In this example, two identical plano-convex first and second lenses 4 are used.
It is configured by arranging a and 4b so that their flat sides face each other. The condenser lens 4 is provided so as to sandwich the image plane IP that is optically conjugate with the film 2.

First and second components of the condenser lens 4
At least one of the lenses 4a and 4b, that is, the second lens 4b in this example, is arranged according to the movement of the exit pupil P1 so as to match the exit pupil P1 of the photographing optical system 1 and the entrance pupil P2 of the relay lens system 6. As indicated by the middle arrow C, they move along the optical axis to relatively change the distance between them. Due to the movement of the condenser lens 4, the matching between the photographing optical system 1 and the relay lens system 6 is maintained well, and the exit pupil P1
It is possible to suppress the light amount loss on the image pickup element 7 due to the movement of

In this embodiment, the lenses 1a and 1b of the photographing optical system 1 are controlled by the control means 10 by controlling the zoom driving means 11 based on the focal length input and set by the photographer. Driven to. The second lens 4b of the condenser lens 4 is also driven in the optical axis direction by the control means 10 controlling the condenser lens driving means 12 in accordance with the set focal length of the photographing optical system 1.

Now, the conditions required for the condenser lens 4 will be described with reference to FIG. Figure 1 (B) shows
It is the figure which expanded the reflection by the mirrors 3 and 5 and showed the optical system of FIG. 1 (A). When the position of the exit pupil P1 of the photographing lens moves in the optical axis direction due to zooming by a zoom lens or lens exchange as in the embodiment, the image plane I is moved from the exit pupil P1.
Since the distance L to P also changes, if the focal length fc of the condenser lens 4 is fixed, the amount of light incident on the relay lens system 6 in the peripheral portion is likely to change.

Therefore, in the optical system of the embodiment, the condenser lens 4 is composed of the first and second lenses 4a and 4b, and the focal length fc can be changed by changing the distance dc between them. The ideal focal length fct in the case where the condenser lens 4 is considered as a thin lens has the distance L from the exit pupil P1 of the photographing optical system 1 to the image plane IP as a variable, and the entrance pupil P2 of the relay lens system 6 from the image plane IP. The distance D up to can be defined as a constant by the following equation (1).

Fct = L · D / (L + D) (1)

However, even if the focal length of the actual condenser lens 4 having a thickness changes by about 10% with respect to the ideal focal length, the amount of peripheral light incident on the relay lens system 6 does not change significantly. Therefore, the range of change of the actual focal length fc of the condenser lens is fct1 when the distance L from the exit pupil P1 to the image plane IP is the minimum, and fct2 when the distance L is the maximum. However, it may be set within a range that satisfies the following condition (2).

[0017] 0.9 · fct1 ≦ fc ≦ 1.1 · fct2 (2)

By setting and changing the focal length of the condenser lens as described above, the exit pupil P1 of the photographing optical system and the entrance pupil P2 of the relay lens system become substantially conjugate,
The amount of light taken into the relay lens system is sufficient up to the periphery.

When the condenser lens is composed of two positive lenses as in the above embodiment, the maximum value dcmax of the distance dc between these lenses is as follows.
It is desirable to satisfy (3).

Dcmax <Lmax-Lmin (3)

However, Lmin is the minimum value of the distance L, and Lmax is the maximum value of the distance L. When this condition (3) is satisfied, the distance dc between the condenser lenses 4 becomes smaller than the moving range of the exit pupil P1 and the observation optical system including the condenser lens 4 can be made compact. If the condition (3) is not satisfied, provision of the condenser lens 4 increases the total length of the observation optical system, making it difficult to make the observation optical system compact.

Further, in order to make the observation optical system more compact, the distance L from the exit pupil P1 of the photographing optical system 1 to the image plane IP and the distance from the image plane IP to the entrance pupil P2 of the relay lens system 6 are used. It is desirable that D and D satisfy the following condition (4).

D / L ≦ 1.3 (4)

When this condition (4) is satisfied, the observation optical system can be made compact. If the condition (4) is not satisfied, the distance D to the entrance pupil P2 becomes too large.
The overall length of the observation optical system becomes long. Further, in this case, since the change in the light amount due to the movement of the exit pupil P1 is relatively small, the reduction in the peripheral light amount is not so large as to pose a problem even if the condenser lens having a relatively weak power is fixedly provided. That is, the movement of the condenser lens 4 according to the configuration of the present invention exhibits its effect most effectively in the optical system satisfying the condition (4).

Next, a concrete configuration example of the optical system of the embodiment will be described. 2 to 4 are diagrams showing the optical system from the photographing optical system 1 to the image pickup device 7 shown in FIG. 1 in which reflection by the mirrors 3 and 5 is developed, and FIG. Shows an intermediate focal length, and FIG. 4 shows an arrangement with a long focal length. Further, FIG. 5 is an enlarged lens diagram showing a portion of the relay lens system 6 in these drawings.

Specific numerical configurations of the lens system are shown in Tables 1 to 3 below. Table 1 shows the configuration of the photographing optical system 1, Table 2 shows the configuration of the condenser lens 4, and Table 3 shows the configuration of the relay lens system 6 and the filter 8 provided on the image plane side thereof. In the table, the symbol r is the radius of curvature, d is the lens thickness and the air gap, n is the refractive index at the d line (588 nm), and ν is the Abbe number.

[0027]

[Table 1]

[0028]

[Table 2] Surface number r d n ν 17 40.000 5.50 1.56883 56.3 18 ∞ variable 19 ∞ 5.50 1.56883 56.3 20 -40.000 66.00

[0029]

[Table 3] Surface number r d n ν 21 11.306 1.65 1.69680 55.5 22 1800.000 0.20 23 5.637 2.03 1.69680 55.5 24 31.120 0.80 25 134.792 1.05 1.80518 25.4 26 3.600 2.13 27 -5.000 1.00 1.59270 35.3 28 36.169 2.09 1.88300 40.8 29 -8.327 0.02 30 12.107 1.53 1.80400 46.6 31 -102.957 3.20 32 ∞ 4.91 1.51633 64.1 33 ∞

With zooming, the distance d8 between the first lens group 1a and the second lens group 1b of the photographing optical system 1 and the distance d between the photographing optical system 1 and the first lens 4a of the condenser lens 4.
16, the distance d18 between the two lenses of the condenser lens 4
(dc) changes as shown in Table 4 below. In this embodiment, the first lens 4a of the condenser lens moves along the optical axis, and the second lens 4b is fixed. Due to the changes in these intervals, the focal length f, f number FNo., Half angle of view ω, back focus fb, and exit pupil P1 of the photographing optical system 1 are changed.
Table 4 also shows the distance L from the image plane IP to the image plane IP, the distance D from the image plane IP to the entrance pupil P2, and the focal length fc of the condenser lens 4.
It changes as shown in.

[0031]

[Table 4] d8 47.40 16.74 4.08 d16 43.98 57.91 57.34 d18 (dc) 0.50 6.00 27.00 f 28.90 52.00 77.60 FNo. 1: 3.7 1: 4.6 1: 4.9 ω 38.2 ° 22.7 ° 15.5 ° fb 43.50 56.40 76.20 L 70.00 82.00 102.00 D 85.00 85.00 85.00 fc 37.14 38.74 46.38

The relationship between the above-mentioned conditional expressions (2) and (4) and the embodiment is as shown in Table 5 below, and all satisfy the conditions. The condition (3) is satisfied because dcmax is 27.00 and Lmax-Lmin is 32.00.

[0033]

[Table 5]

FIG. 6 is a ray tracing diagram in the optical system of the embodiment shown in FIG. 2, where (A) is a short focal length, (B) is an intermediate focal length, and (C) is a long focal length. Shows. 7 to 9 are graphs showing the relationship between the light amount attenuation and the image height by vignetting and the cosine fourth law at each focal length. The horizontal axis of each graph is the image height
(Unit: mm), and the vertical axis represents the light amount ratio (unit:%). The solid line in the graph shows the vignetting, and the broken line shows the effect of the cosine fourth law.

FIG. 10 is a ray tracing diagram in the optical system of the comparative example in which the condenser lens 4'having one lens is fixedly provided. (A) is a short focal length and (B) is an intermediate focal length. , (C) show the state at the long focal length. 11 to 13 are similar to FIGS. 7 to 9 showing the relationship between the image height and the attenuation of the light quantity by vignetting and the cosine fourth law at each focal length when the condenser lens is fixed. Is a graph of.

By comparing these graphs, the condenser lens is divided into two or more pieces and relatively moves on the optical axis, so that the performance at the position where the image height is high, that is, the peripheral light amount is improved. Understand that

FIG. 7 and FIG. 11 show almost the same performance. This is because the focal length of the condenser lens of the comparative example is determined on the basis of this short focal length. However, in the comparative example, as the focal length becomes longer, the light amount in the portion where the image height is high decreases as shown in FIG. 12, and the long focal length shown in FIG. 13 significantly decreases. On the other hand, in the embodiment, even when the focal length becomes long, the peripheral light amount is hardly attenuated as shown in FIGS. 8 and 9.

[0038]

As described above, according to the present invention, the condenser lens in the observation optical system is divided into a plurality of lenses, and the relative distance is changed according to the movement of the exit pupil of the photographing optical system. It is possible to suppress the attenuation of the light amount in the peripheral portion of the image observed by the observation optical system due to the movement of the exit pupil.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an optical system showing an embodiment of a compound optical system for a camera according to the present invention.

FIG. 2 is a lens diagram at a short focal length, showing a specific configuration example of the embodiment shown in FIG.

FIG. 3 is a lens diagram showing a specific configuration example of the embodiment shown in FIG. 1 at an intermediate focal length.

FIG. 4 is a lens diagram at a long focal length showing a specific configuration example of the embodiment shown in FIG.

5 is a lens diagram showing only a relay lens system in the lens diagram shown in FIG. 2 in an enlarged manner.

6A and 6B are ray tracing diagrams of the optical system of the embodiment, where FIG. 6A is a short focal length, FIG. 6B is an intermediate focal length, and FIG.
Shows each state at the long focal length.

FIG. 7 is a graph showing the relationship between image height and vignetting in the state of FIG. 10A and attenuation of light amount in the peripheral portion according to the cosine fourth law.

FIG. 8 is a graph showing the relationship between image height and vignetting in the state of FIG. 10B and attenuation of light amount in the peripheral portion according to the cosine fourth law.

FIG. 9 is a graph showing the relationship between the image height and the vignetting in the state of FIG. 10C and the attenuation of the light amount of the peripheral portion according to the cosine fourth law.

FIG. 10 is a ray tracing diagram of an optical system in which one condenser lens is fixed, (A) at a short focal length, (B) at an intermediate focal length, and (C) at a long focal length. Each state of is shown.

FIG. 11 is a graph showing the relationship between image height and vignetting in the state of FIG. 10A and attenuation of light amount in the peripheral portion according to the cosine fourth law.

FIG. 12 is a graph showing the relationship between image height and vignetting in the state of FIG. 10B and attenuation of light amount in the peripheral portion according to the cosine fourth law.

FIG. 13 is a graph showing the relationship between image height and vignetting in the state of FIG. 10C and attenuation of light amount in the peripheral portion according to the cosine fourth law.

[Explanation of symbols]

1 Shooting optical system 1a First lens group 1b Second lens group 2 films 3,5 mirror 4 condenser lens 4a first lens 4b second lens 6 relay lens system 7 Image sensor 8 filters

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-133928 (JP, A) JP-A-3-37607 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03B 13/00

Claims (10)

(57) [Claims] 1. A first optical system for forming a subject image on an imaging surface, an optical path separating means for separating a light beam incident through the first optical system from an optical path toward the imaging surface, and the optical path separation. A second optical system for guiding a light beam from the subject separated by a means, wherein the second optical system is provided with a condenser lens including at least two independent lenses. At least one lens of the condenser lenses moves in the optical axis direction in accordance with the position of the exit pupil of the first optical system to relatively change the distance between the lenses. A complex optical system for cameras. 2. The second optical system includes a relay lens for re-imaging the image formed by the first optical system behind the condenser lens, and an image re-formed by the relay lens. The compound optical system for a camera according to claim 1, further comprising: an image pickup device for picking up an image. 3. The first optical system is a zoom lens system capable of zooming, and each lens of the condenser lenses has a continuous interval between the lenses according to zooming of the first optical system. The compound optical system for a camera according to claim 1, wherein 4. The compound optical system for a camera according to claim 1, wherein the condenser lens is constituted by providing positive lenses of the same shape so as to face each other. 5. A composite focal length f of the condenser lens
c is the distance L from the exit pupil of the first optical system to the image plane
The compound optical system for a camera according to claim 2, wherein the compound optical system changes so as to satisfy the following condition. fc = L · D / (L + D) where D: distance from the image plane to the entrance pupil of the relay lens system. 6. The condenser lens is composed of two positive lenses, and the distance d between the lenses is the maximum value of L.
6. The compound optical system for a camera according to claim 5, wherein the condition of d <Lmax-Lmin is satisfied, where max and the minimum value are Lmin. 7. A condition of D / L ≦ 1.3 where L is a distance from an exit pupil of the first optical system to an image plane and D is a distance from the image plane to an entrance pupil of the relay lens system. The compound optical system for a camera according to claim 1, wherein: 8. The first optical system is a variable magnification zoom lens system, and the condenser lens is at least 2
8. The compound optical system for a camera according to claim 7, wherein the compound optical system comprises a plurality of lenses, and a relative distance between the lenses is changed according to zooming of the first optical system. 9. A variable-magnification optical system capable of changing the magnification of the object image by forming an object image on an imaging surface and moving at least one lens in the optical axis direction, and the variable-magnification optical system. And an optical path separating means provided between the image pickup surface and the image pickup surface, and arranged in the optical path separated by the optical path separating means,
A compound optical system for a camera, comprising: at least two condenser lenses that relatively move in the optical axis direction so as to suppress a change in the amount of light in accordance with the movement of the exit pupil of the variable power optical system in the optical axis direction. . 10. The compound optical system for a camera according to claim 9, wherein the condenser lens is composed of two positive lenses.