JPS59121015A - Photographic lens subjected to short distance correction - Google Patents

Abstract

PURPOSE:To correct satisfactorily various aberrations even in case of photographing of a short distance, and to make a titled lens durable enough even in a state that a diaphragm is opened by setting a prescribed air space by a refererence image magnification state between a positive lens component of an object side and a lens group of an image side, reducing the space at the time of focusing to a short distance object, and also magnifying the space behind a negative lens component. CONSTITUTION:As for a deformed Gauss type lens of an F1.4 class, the image surface moves in the positive direction as an image magnification is raised, therefore, the image surface is corrected to the negative direction by magnifying an air space d6 behind a negative maniscus lens L3, and also an asymmetrical property of a comatic aberration is corrected. In this case, the lenses L2, L3 can be moved to the front side as one body in a state that the lenses L1, L4-L7 remain fixed by setting a correcting amount of an air space d2 between a positive lens L1 and a positive meniscus lens L2, and a correcting amount of the space d6 to the same amount, and also the correcting amount can be decided independently to the lenses L2, L3, respectively. Accordingly, in a fast photographic lens of an area extending from a standard to a telephoto, various aberrations are corrected satisfactorily even in case of a short distance photographing, and an excellent image-forming performance can be maintained at all times.

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 shooting at an infinite distance, their performance deteriorates significantly when shooting at close range, that is, when the 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, and short-range correction is not possible with a simple configuration. It was difficult to do.

An object of the present invention is to solve the above-mentioned drawbacks by providing a view angle of 11°.
The large aperture of the ~50° standard lens or telephoto lens effectively corrects various aberrations even when shooting at closer distances, as well as when shooting at standard magnification such as infinity shooting, and is sufficiently large for practical use even when the aperture is wide open. Our goal is to provide a photographic lens of the same standard.

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.
This provides a new means of correction for close-up photography.

That is, the present invention is a so-called standard lens to a telephoto lens with an angle of view of about 11° to 50°, has a brightness of F2.0 or more, and has a positive lens component closest to the object 1111 and a lens behind it. In a photographic lens having a negative lens component in the lens group, a predetermined air gap is provided between the positive lens component closest to the object side and the lens group closer to the image side in a standard shooting magnification state, for example, in a focused state at infinity. By reducing this air gap when focusing on an object at a closer distance, and by fully expanding the air gap after the negative lens component (3), various aberrations when focusing on a closer distance can be reduced. This is to correct deterioration.

Generally, it has a positive lens component at the most object eye 11 and a negative lens component in the lens group on the image side, and the angle of view is 11° to 50°.
In a lens base with a brightness and an F number of 2.0 or higher, as the imaging magnification is increased, the spherical aberration changes in the negative direction, and the asymmetric coma aberration also increases accordingly. 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 photography, the above-mentioned spherical aberration that changes in the negative direction is corrected, and the asymmetric Reduces coma aberration. By reducing the distance between the most positive lens component of the object 1111 and the following lens component, the paraxial ray after passing through this positive lens component passes through a position further away from the optical axis in the subsequent negative lens component. As a result of this, the spherical aberration is corrected in the positive direction, and the asymmetry of comatic aberration is also reduced accordingly (4).

This is sufficient for lens bases where the image plane changes little due to magnification, or for magnification ranges where changes are not a problem, but for lens bases where the image plane changes significantly and associated asymmetrical coma aberration is significant, or for such magnification ranges. Therefore, 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 of the image fill in the lens system beyond the gap correction point.

Specifically, since the direction of change in the image plane due to a change in magnification varies slightly depending on the various lens types, it is necessary to select an appropriate correction location for each lens type based on the above basic idea.

For example, in the case of so-called modified Gauss type lenses with large aperture ratios such as Fl and 4 classes, the image plane generally moves in the positive direction as the photographing magnification increases.
As in the first embodiment shown in the figure, the negative meniscus lens L3
By enlarging the air gap d6 after the d6, the image plane can be corrected in the negative direction, and at the same time, the asymmetry of comatic aberration can be further corrected. Here, a positive lens L1 and a positive meniscus lens L are used.

The amount of correction for the air space d2 between the lenses and the amount of correction for the aperture space d are the same, and the lens "I + "4 +L, , L6
．． The one who fixed L7! Alternatively, lenses L2 + L3 may be moved forward as a unit, or lenses L2 and L3 may be moved forward as a unit.
The correction amount may be determined independently for each. Even with the same Gauss type lens, the image plane may change in the negative direction due to a change in magnification, as in the second embodiment shown in FIG.

In this case, a negative meniscus lens is used, and an air gap d after the negative lens is made up of a negative meniscus lens and a positive meniscus lens L5.
By expanding , the image plane can be corrected in the positive direction and the overall balance can be maintained. In the second embodiment, both outer positive lenses, LI + "6" are fixed and the remaining lens 2 is used.
The correction may be performed by moving r' ``3 + ``4 + ''5 as a unit, or may be corrected individually by changing the amount of correction.

Above 1. In FIGS. 1 and 2 showing the second embodiment, (A) is a lens configuration diagram, (B) and (C) are both aberration diagrams at an imaging magnification of β-17.0, and (B )V
This is the case where the entire i-relen system is integrally extended and focused, (0 is the case where the short distance correction according to the present invention is performed and the image is focused.

The intervals between the marks in each lens configuration diagram indicate variable intervals for correction. In addition, each aberration diagram shows spherical aberration (Sph).
, astigmatism (Ast), and coma aberration (Cowa), and in the coma aberration diagram, lateral aberration of spherical aberration is also shown with a dotted line for comparison of symmetry. (The same applies to the embodiments described later.) The third embodiment of the present invention has a scenario as shown in FIG.
This is a large aperture ratio telephoto lens that can also be called an Ernostar type or Ernostar type, and the fourth embodiment is a large aperture ratio quasi (
7) It is a telephoto lens. The third of these. In the fourth embodiment, as in the above-mentioned embodiments, as the photographic magnification is increased, the image plane changes in the negative direction, but in the third embodiment, the positive lens L4
The image plane is corrected in the positive direction by widening the air gap d8 after the negative lens component consisting of the bonded negative lens L and the negative meniscus lens L4 in the fourth embodiment. This improves the balance between spherical aberration and image plane, as well as the balance between coma aberration. 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 L1 and L6 are fixed, and the remaining lenses L2 to L5 of the inner fII 11 are moved as a unit. Correction can be made by fixing both outer 1111I positive lenses L, L, and moving the remaining inner lenses L2 to L4 as a unit, or by changing the amount of correction for the front and rear air gaps individually. What may be done is the same as in the case of (8) (8) and the second embodiment.

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 thickness and air gap of each lens,
n and ν are each da (λ=587.6., nm)
The refractive index and the number are shown in the figure, and each subscript number shows the order from the object side.

i, 4, J-11119 ri shu sō ri 0 hit
0 ■ To 0-- To the size N Size (I) ■ ■≧ Yu ≧
Δ for ≧ ℃ zu0
Ku Ku! 1 1 Dimension II II II II II II I
I II II II II II II II
-4 mouths-tJ-II II 11 1111 1
1111 q ko 1 J--1 - 1 ~ ψ 啼 喰 ro
Go to 1111
< Ku■ l+-7 II II II II II I
I II II II (11) Me
11110fu II II II II II I
I II II II (12) From the comparative aberration diagrams of each example, spherical aberration, curvature of field (balance between meridional image surface and sagittal image surface), and coma aberration before correction by the present invention (each diagram (B)) It can be seen that the balance is much better after correction (each figure (C)).

As mentioned above, the distance correction amount depends on each lens type and specification.
Furthermore, the following ranges are desirable for the type, specifications, and magnification (β=−heat) of each embodiment, although it varies depending on the amount of change in aberration due to change in magnification. However, both of the two variable intervals are represented by △. f is the focal length of the entire system.

[Example 1] 0ku△(2,4f [Example 2] O〈△(1,4f [Example 3]) 0〈△(1,2f [Example 4] 0〈△〈0.7f 1st In the embodiment, the first interval d2 exceeds two limits.
When the correction amount is increased, the spherical aberration changes in the positive direction, but the image plane moves in the negative direction.・This is not preferable because the correction balance in the surrounding areas will be disrupted. It's good, number two. Third. In the fourth embodiment, since both the spherical aberration and the image plane move in the positive direction when correcting the first distance d2, if the correction exceeds the upper limit, even if the distance after the rear negative lens component is widened. The image plane cannot be fully corrected in the negative direction, and the overall aberration balance is not good.

As described above, according to the present invention, in a large aperture ratio photographic lens ranging from standard to telephoto, various aberrations are well corrected even during close-range shooting, and excellent imaging performance can always be maintained.

In the above embodiments, the design standard is an infinity shooting state, but the design standard is not limited to this, but the design standard is a certain close-range shooting state that provides a predetermined shooting magnification, and it is possible to The correction method of the present invention can also be applied when photographing at a close distance, that is, at a higher magnification (15).

[Brief explanation of the drawing]

1 to 4 show cross-sectional views and aberration diagrams of lenses of the first to fourth embodiments of the present invention, respectively, (A) is a cross-sectional view of the lens structure, (B) and ((j is Spherical aberration and astigmatism at the magnification, that is, β-'/10, are shown in each example.
Aberration diagrams of coma aberration are shown before and after correction, respectively. [Explanation of symbols of main parts] Fig. 1 (In Shu L3...Negative meniscus lens d,...Air spacing (aperture space) L,...Positive lens L2...Positive meniscus lens d2...Air spacing (16 )

Claims (1)

[Claims] In a photographic lens that has a positive lens component closest to the object side and a negative lens component in the rear lens group, a predetermined amount of air is placed between the positive lens component and the lens group on the image side at the standard photographing magnification state. The lens is characterized by setting an interval, and reducing the air interval when focusing on a closer object, and expanding an air interval after the negative lens component to correct aberrations when focusing on a closer distance. A photographic lens.