JPH0553242B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photographic lens whose performance is improved by moving a part of the lens system during close-range photography. Recently, the performance of photographic lenses has become extremely superior due to the remarkable development of electronic computers. However, since photographic lenses are generally designed for photographing at infinity, the performance deteriorates significantly when photographing at close range, that is, when the photographing magnification is increased. This tendency becomes more pronounced as the aperture ratio lens becomes larger, making it impractical to use the lens with the aperture wide open, which is particularly inconvenient when photographing dark subjects at close range. Regarding wide-angle lenses, so-called reverse telephoto types, a method of changing the spacing of some lenses during focusing has been used for a long time to correct aberrations in close-up shooting conditions, and recently it has moved into the area of standard lenses. Various short-range corrections have also been proposed. However, in order to improve close-range performance with a standard lens or a large aperture ratio lens with a slightly longer focal length than this, it is necessary to complicate the lens configuration in order to improve close-range performance with the aperture open. It was difficult to do. An object of the present invention is to solve the above-mentioned drawbacks by using a standard lens or a telephoto lens with an angle of view of about 11° to 50°, as well as shooting conditions at a standard magnification such as infinity shooting.
The object of the present invention is to provide a photographic lens with a large aperture ratio that satisfactorily corrects various aberrations even when photographing at closer distances and is sufficiently usable for practical use even when the aperture is opened. As described below, the present invention has discovered that by relatively moving specific lens groups, these aberrations that worsen in close-up shooting conditions can be very well corrected, and the present invention has developed a new method for close-up shooting. This provides a suitable correction means. In other words, the present invention is a so-called standard lens to a telephoto lens with an angle of view of about 11° to 50°, has brightness at F2.0 or higher, and has a positive lens component closest to the object and a lens group behind it. In a photographic lens that has an aperture and a negative lens component inside, there is a predetermined air gap between the positive lens component closest to the object and the lens group closer to the image in a standard photographic magnification state, for example, in a focused state at infinity. By setting , and reducing this air gap when focusing on an object at a closer distance, and expanding the air gap after the negative lens component, that is, on the image side,
This corrects the deterioration of erroneous aberrations during short-distance focusing. Generally, it has a positive lens component closest to the object side and a negative lens component in the lens group on the image side, and has an angle of view of 11° ~
With a lens system that is approximately 50° and brighter than F number 2.0, the spherical aberration will change in the negative direction as the entire lens system moves integrally to perform short-range focusing and increase the imaging magnification. Along with this, asymmetric coma aberration also increases. In the present invention, first of all,
By reducing the air distance between the positive lens component closest to the object and this rear lens group during close-range shooting, the above-mentioned negative-varying spherical aberration can be corrected, as well as asymmetric coma aberration can be reduced. There is. By reducing the distance between the most object-side positive lens component and the following lens component, the paraxial rays after passing through this positive lens component will move further away from the optical axis in the subsequent negative lens component. As a result of the stronger divergence effect here, spherical aberration is corrected in the positive direction, and the asymmetry of comatic aberration is also reduced accordingly. This is sufficient for lens systems in which the image plane changes little due to magnification, or in a magnification range where the change is not a problem, but for lens systems in which the image plane changes significantly and the associated asymmetrical coma aberration is significant, or in such a magnification range. Then, in addition to the above-mentioned interval correction, it is necessary to devise a method for further correcting this. For this reason, in the present invention, secondly, this deterioration is prevented by additionally moving the air gap after the negative lens component on the image side of the gap correction point in the lens system in the direction of widening. Specifically, since the direction of change in the image plane due to changes in magnification differs slightly depending on the various lens types, it is necessary to select an appropriate correction point for each lens type based on the above basic idea. is necessary. For example, in the so-called deformed Gauss type lens with a large aperture ratio in the F1.4 class, the image plane generally moves in the positive direction as the imaging magnification increases due to the integral movement of the entire lens system toward the object side. In this case, as in the first embodiment shown in FIG. 1, the image plane is corrected in the negative direction by enlarging the air gap d ₆ after the negative meniscus lens L ₃ , and the asymmetry of coma is also corrected. can be further corrected. Here, the correction amount for the air gap d ₂ between the positive lens L ₁ and the positive meniscus lens L ₂ and the correction amount for the aperture space d ₆ are set to the same amount, and the lenses L ₁ , L ₄ , L ₅ , L ₆ , L The lenses L ₂ and ₃ may be moved relatively to the front side while the lens ₇ is integrated, or the correction amounts may be determined for the lenses L ₂ and L ₃ individually. Even with the same Gauss type lens, as in the second embodiment shown in FIG. 2, the image plane may change in the negative direction due to a change in magnification caused by integral movement of the entire lens system. In this case, it is possible to correct the image plane in the positive direction and maintain overall balance by widening the air gap _d9 after the negative lens, which is made up of a negative meniscus lens _L4 and a positive meniscus lens _L5 . I can do it. In the second embodiment, correction may also be made by integrating the positive lenses L ₁ and L ₆ on both sides and moving the remaining lenses L ₂ , L ₃ , L ₄ , and L ₅ relatively as a unit. However, the correction may be performed individually by changing the correction amount. Figures 1 and 2 show the first and second embodiments above.
In the figure, A is a lens configuration diagram, B and C
Both are aberration diagrams at photographic magnification β = -1/10, B is the case where the entire lens system is extended as a unit and focused, and C is the case where the close distance correction according to the present invention is performed and the image is focused. It is. The intervals marked with * in each lens configuration diagram indicate variable intervals for correction. In addition, each aberration diagram shows spherical aberration (Sph), astigmatism (Ast),
Comatic aberration (Cowa) is shown, and transverse aberration of spherical aberration is also shown with a dotted line in the coma aberration diagram for comparison of symmetry. (The same applies to the embodiments described later.) The third embodiment of the present invention is a large-diameter telephoto lens that can be called a Sonnar type or Ernostar type as shown in FIG. The fourth embodiment is a semi-telephoto lens with a large aperture ratio, which is a modification of the so-called Xenotar type as shown in FIG. In these third and fourth embodiments, as in the above-mentioned embodiments, when the photographic magnification is increased by integrally moving the entire lens system toward the object side, the image plane changes in the negative direction. , in the third embodiment, the air spacing d 8 after the negative lens component consisting of the positive lens L ₄ and the negative lens L ₅ bonded together, and in the fourth embodiment, the air spacing d ₈ after the negative meniscus lens L ₄ By expanding each of _{the 8} , the image plane is corrected in the positive direction, and the positive lens
By reducing the image-side air spacing of _L1 , the balance between spherical aberration and image surface, and the balance between coma aberration are improved. As seen in the aberration diagrams of FIGS. 3 and 4, the aberrations are much better after the correction than before the correction, and the extent of the effect can be clearly seen. Here too, the amount of correction for both the front and rear air gaps is the same, and in the third embodiment, both outer positive lenses L ₁ and L ₆ are integrated, and the remaining inner lenses L ₂ to _{L 5} are integrated and relatively moved. In the fourth embodiment as well, the correction may be made by integrating the positive lenses L ₁ and L ₅ on both the outer sides and moving the remaining inner lenses L ₂ to _{L 4} as one unit and relatively.
As in the first and second embodiments, the correction amounts for both the front and rear air gaps may be changed and corrected individually. The specifications of each of the above embodiments are shown below. In each table, r
is the radius of curvature of each lens surface, d is the center and thick air distance of each lens, n and ν are the d-line (λ =
587.6 nm), and each subscript number represents the order from the object side.

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[Table] 〓

Claims (1)

[Claims] 1. A photographic lens having a positive lens component disposed closest to the object side and an image-side lens group disposed on the image side including an aperture and a negative lens component, wherein the positive lens component and A predetermined air gap is set between the positive lens component and the image side lens group in a standard imaging magnification state, and the air gap between the positive lens component and the image side lens group is reduced when focusing on a closer object. Aberrations during close-range focusing are corrected by enlarging the image-side air gap of the negative lens component in the image-side lens group, and the respective gap correction amounts of the reducing air gap and increasing air gap are respectively △ 1. A photographic lens characterized by satisfying the following conditions: 0<Δ1, Δ2<0.024f, where f is the focal length of the photographic lens.