JPS584114A - Visibility adjustable finder for single-lens reflex camera - Google Patents

Abstract

PURPOSE:To obtain an optical system of which aberration is efficiently compensated and visibility can be continuously adjusted by shifting the 1st lens group on the optical axis of a finder in the finder optical system provided with the 1st lens group consisting of negative lenses and the 2nd lens group consisting of 2 positive lenses. CONSTITUTION:In a finder optical system consisting of the 1st lens group A having the expansion block P of a penta roof prism and a negative lens G1 and the 2nd lens group B having 2 positive lenses G2, G3, a f2<f3 condition is satisfied and visibility is adjusted by shifting the 1st lens group on the optical axis of the finder when the focal distance of a positive lens on the penta roof prism in the 2nd lens group is f2 and the focal distance of the other positive lens is f3. In addition, it is perferable to satisfy R5<¦R6¦(R6<0) and R7<=¦R8¦ to compensate various averrations of an eyepiece when radiuses of curvature of respective lens surfaces in the 2nd lens group are R5, R6, R7, R8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder optical system for a single-lens reflex camera, and more particularly to a finder optical system in which diopter adjustment is performed by moving a part of an eyepiece lens in the direction of the finder original axis.

In general, to observe a subject image in the finder optical system of a -IN reflex camera, the subject image is focused on the focus plate and is passed through a pentagonal roof prism through an eyepiece lens at approximately -1
The image is formed at the position of the dayopter. However, if the observer has strong myopia or farsightedness or a weak ability to adjust the diopter, it will be difficult to observe the subject image formed at around 11 diopters with the naked eye.

For this reason, the viewfinder optical system of conventional single-lens reflex cameras required an attachment lens to be attached to the rear of the eyepiece to adjust the diopter. However, the diopter cannot be adjusted continuously and the eye point position for observation is short, making it difficult to observe the field of view well.

On the other hand, as a method for continuously adjusting the diopter of the finder optical system, there is a method of moving the eyepiece back and forth on the finder original axis. The crosspiece change ΔDp at this time is the focal length of the eyepiece lens fe(-).

If the amount of movement on the finder original axis is △S (■) It is expressed as ΔDp=1000・ΔS/fe.

In the case of an ocular reflex camera (version 35), the focal length of the eyepiece is approximately 60 m based on the optical path length of the pentagonal roof prism provided between the eyepiece and the focusing plate. For this reason, in order to provide a predetermined change in diopter, the eyepiece must be moved significantly, which requires a large space behind the pentagonal roof prism, which is difficult to realize in a small single-lens reflex camera.

For example, to provide a diopter change of +/-1 diopter, the eyepiece must be moved about 7 inches.

As a method to reduce the amount of movement of the II eye lens.

Japanese Patent Publication No. 55-67732. Several proposals have been made, such as in %Open 11B-126531. In these proposals, the eyepiece is composed of a single lens with negative refractive power and a single lens with positive refractive power on the side of the penta roof prism, one of which is fixed and the other is moved along the viewfinder optical axis to adjust the diopter. It is carried out. However, since the various aberrations of the finder optical system in the standard state are large, and the various aberrations fluctuate greatly as the diopter changes, the image performance during finder observation cannot be said to be fully satisfactory.

The present invention includes an eyepiece lens with adjustable diopter. The object is to obtain a finder optical system with good aberration correction.

The feature of the structure of the present invention is that the eyepiece lens is composed of two lens groups, and each lens group is given appropriate refractive power and lens shape, and some of the lens groups are moved on the optical axis of the finder. This is due to the fact that the temperature is being adjusted.

An embodiment of the present invention will be described below in detail with reference to each drawing.

1 to 3 are schematic diagrams of a portion of a finder optical system according to a first embodiment of the present invention, and FIGS. 7 to 9 are schematic diagrams of a portion of a finder optical system according to a second embodiment of the present invention.

In the figure, F is the focus plane of the finder, P is the block of the expanded penta roof prism, A is the first lens group, B is the second lens group, Gl is the negative lens of the second lens group A, G2.
G3 is a positive lens of the second lens group B.

■ is one side of the viewfinder.

The eyepiece in the embodiment has @2 fixed lens groups,
Visual adjustment is performed by moving the second lens group on the finder axis, but at this time, the focal length tf of the positive lens on the penta roof prism side of the second lens group, and the other positive When the focal length of the lens is t fs (1
) A finder optical system has been achieved that satisfies the condition ft < fm and performs good aberration correction even when the diopter changes.

Since the eyepiece of a conventional finder optical system consists of two lens groups: the first lens group with negative refractive power and the second lens group with positive refractive power, many aberrations occur in the first lens group, and especially The spherical aberration of the plastyopter caused a decline in the performance of the viewfinder.

The tangent lens of the present invention is composed of two lens groups: a first lens group with a negative refractive power and a second lens group with a positive refractive power including two positive lenses. Reduces spherical aberration. Also, in this case, the relationship between the refractive powers of the two positive lenses is set by making the refractive power of the positive lens on the penta roof prism side stronger than the refractive power of the other positive lens, that is, the conditional expression (1) that ft < fs is given. This prevents the distance between the principal points of the first lens group and the second lens group from widening, and prevents the focal length of the eyepiece from increasing and the finder magnification from decreasing. Furthermore, the occurrence of asymmetric aberrations is prevented.

With the above configuration, the object of the present invention can be achieved, but in order to better correct various aberrations of the eyepiece lens, the radius of curvature in each lens direction of the second lens group is set in order from the pentagonal roof prism side to about, Ra, When Rv is 1'% (2) R, <lLl &<.

(3) &<1Ral It is preferable to satisfy the following conditions.

Conditional expression (2) 1 Conditional expression (8) is the source of conditional expression (1) 2
Off-axis aberrations are well corrected by strengthening the lens Ifi on the pentadano prism side of each of the divided positive lenses. If the shape deviates from either conditional expressions (2) or (8), off-axis aberrations will worsen.

This will cause the finder's compensation performance to deteriorate.

Next, the embodiments shown in each figure will be described.

@ Figure 1, Figure 2, and Figure 3 each show the schematic teeth of the optical system of Example 1 of the present invention, in order of 11 diopters.

This shows the state of the optical system at -3 day opter and +1 day opter, and 1! ! Crystal aberrations are shown in FIG. 4, FIG. 5, and FIG. 6 in order. In the example, the focal length ft of the positive lens on the pentagonal roof prism side of the second lens group is f1±4&2
2. Focal length f of the other positive lens in the second lens group, dew 14
U, 07, ft < fs.

FIG. 7, FIG. 8, and FIG. 9 are schematic diagrams of an optical system according to a 20th embodiment of the present invention, and show the 11th and 1st targets in order.

Figure 10 shows the state of the optical system when it is -3 day opter and +1 day opter, and the various aberrations at this time are shown in order.
12. In Example 2, the focal length f of the positive lens on the pentagonal roof prism side of the second lens group is f,
=4a20. Focal length f of the other positive lens in the second lens group
, fa=88.47 and fs<fs.

As described above, according to the present invention, a wide diopter adjustment range can be obtained with a simple lens configuration, and as shown in the figure, a single-lens reflex camera with adjustable diopter has well-corrected aberrations over a wide diopter adjustment range. Finder system can be obtained.

Next, numerical examples of each embodiment of the present invention will be shown.

In the numerical examples, Ri is the radius of curvature of the first optical member counted from the left side in the figure, Di is the first optical member and air distance counted from the left side in the figure, and Ni and vl are respectively These are the refractive index and Atsube number of the first optical member counted from the center left side.

Example I D, = 5.0 Example 2 DI+-Kan O

[Brief explanation of drawings]

FIGS. 1, 2E, and 3 respectively show the first embodiment of the present invention.
Schematic diagrams of the optical system at IDp, -3Dp, and +IDp; Figures 4, 5, and 6 are diagrams of various aberrations at -IDp, -3Dp, and +IDp of the first embodiment of the present invention; Figure 7; 8 and 9 are schematic diagrams of the optical systems in -IDp, -3Dp, and +IDp of the second embodiment of the present invention, respectively, and FIGS. 10, 11, and 12 are schematic diagrams of the optical systems of the second embodiment of the present invention, respectively. It is a diagram of various aberrations at −IDp, −3Dp, and +IDp in examples. In the figure, F is the finder bottle) [ffi, Pti block with penta roof prism expanded. A is the first lens group, B is the second lens group, Gl is the negative lens of the second lens group A, G2. G3t1 are each a positive lens of the second lens group B, and one surface of the IH sofa folder. Figure 1: Peek-a-glance on the ridge, eaves, cursed claws, distortion/sniff protection spell 1
1 yeast, 1 strain, 0 yields, 1 ball visit, 41 gentlemen, 1
Seikun Sei I Yumi Kawaf! , income-ra% t5 Kusuru Taiko

Claims (1)

[Scope of Claims] (1) In a finder optical system in which diopter adjustment is performed by moving an eyepiece disposed behind the exit surface of a penta roof prism on the finder original axis, the eyepiece has a negative refraction from the penta roof prism side. a second lens group having a positive refractive power and a second lens group having a positive refractive power, the second lens group having one negative lens, and the second lens group having two positive lenses; A diopter adjustment characterized by a diopter that satisfies the condition fz < fs, where f is the focal length of the positive lens on the pentagonal roof prism side of the second lens group, and f is the focal length of the other positive lens of the second lens group. Possible finder of a single-lens reflex camera (3) When the radius of curvature of the lens of the second lens group is &, Rs, &, Ra in order from the penta roof prism side, R1<IRI l, Rs<0 &<I bird l The first claim characterized in that the following conditions are satisfied:
Viewfinder for a single-lens reflex camera with adjustable diopter as described in Section 1. (8) The finder of a single-lens reflex camera with adjustable diopter according to claim 1, wherein the view angle is adjusted by moving the first lens group on the original axis.