JPS6048730B2 - SLR camera viewfinder with adjustable diopter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder for a single-lens reflex camera that allows diopter adjustment by moving a portion of the eyepiece in the optical axis direction.

In general, the finder of a single-lens reflex camera is designed to observe an object image formed on a pit plate by focusing it on an eyepiece lens through a pentagonal roof prism at around -1 dayopter (Dp).

However, it is difficult for observers with severe nearsightedness, farsightedness, or weak diopter adjustment ability to observe a subject image formed in the vicinity of -1 diopter with the naked eye. For this reason, conventional single-lens reflex camera finders use an attachment lens behind the eyepiece to adjust the diopter, but continuous diopter adjustment is not possible. Also, the eye point position becomes short7, making it difficult to see the field of view. The diopter adjustment of the finder is possible by moving the eyepiece back and forth on the finder optical axis with respect to the subject image, and the diopter change ΔDp at this time is determined by setting the focal length of the eyepiece to fe (-) and adjusting the viewfinder light. If the amount of movement θ on the axis is ΔS (agony), then ΔD
p■1000ΔS/f.

2 It is expressed as

In the case of a 35wgn-ocular reflex camera, the focal point and distance of the eyepiece are around the mark - due to the optical path length of the penta roof prism installed between the eyepiece and the pit plate, so the required diopter change can be obtained. This required a large amount of movement and a large amount of space behind the pentagonal roof prism, making it extremely difficult to realize.

For example, in order to obtain a diopter change of ±1 dayopter, it is necessary to move the eyepiece lens by about 7 TWL from the above calculation formula. The solution to this problem was published in Japanese Patent Application Laid-Open No. 55-6773.
According to these proposals, the eyepiece is constructed from a concave single lens and a convex single lens from the penta roof prism side, one of which is fixed and the other is connected to the viewfinder optical axis. It moves the top.

However, due to aberrations in the standard diopter state and changes in diopter, it cannot be said that sufficient consideration has been given to aberration changes when the lens is moved, and the viewfinder image is lower than the viewfinder of a single-lens reflex camera that does not adjust the diopter. There was a drawback of poor performance. An object of the present invention is to eliminate the drawbacks of the conventional example by moving a part of the eyepiece lens in the optical axis direction to correct the diopter, and to provide a single lens capable of adjusting the diopter with good aberration correction and good visibility. The purpose of this invention is to provide a finder for reflex cameras.

In order to achieve the above object, the present invention provides a viewfinder for a single-lens reflex camera in which the diopter is adjusted by moving an eyepiece placed behind the exit surface of a penta roof prism on the optical axis of the viewfinder. The eyepiece is constituted by three groups, sequentially from the penta-roof prism side: a first group consisting of a negative single lens, a second group consisting of a positive single lens, and a third group consisting of a positive single lens. The second group and the third group are fixed, and the diopter is adjusted by moving the second group on the viewfinder optical axis, and the focal length of the second group is set to F.

, the focal length of the third group is F. When (1) F2<F
.

These conditions are now being met.

Since the eyepiece of a conventional finder consists of two groups, a single negative lens and a single positive lens, large aberrations occur in the positive lens group, especially spherical aberration of the positive diopter.
This affected the image performance of the finder and worsened visibility.

Therefore, the eyepiece of the present invention is composed of three groups including two positive lenses, and basically 4. is intended to reduce the positive spherical aberration that occurs in the positive lens, and to correct the spherical aberration of the eyepiece to a small value. It is. At this time, in the relationship between the refractive powers of the positive lenses of the second group and the third group, by making the refractive power of the second group stronger than that of the third group, that is, by providing a condition peak, This prevents the amount of movement of the second group from increasing in order to obtain the required diopter adjustment. Furthermore, the distance between the principal points 7 between the negative lens group and the positive lens group is prevented from increasing, thereby preventing the focal length of the eyepiece from increasing and the finder magnification from decreasing, and also preventing the occurrence of asymmetric aberrations.
Furthermore, in order to better correct the aberration of the eyepiece lens, the second
When the radii of curvature of the group and the third group are respectively R,,R,O and R,,,R,2 from the pentada haptic crism side,
(2) R9<IR,Ol (3) R, , <IR, 2l It is desirable to satisfy the following conditions.

7 Conditions (2) and (3) are achieved by making the positive lenses of the second and third groups determined based on condition (1) into shapes with stronger surfaces on the pentagonal roof prism side. Aberrations are corrected to a minimum.

The present invention will be explained in more detail below with reference to the drawings.

FIGS. 1 to 3 are optical path diagrams of the first embodiment in the developed state, and are in the -1 dayopter, +1 dayopter, and -3 dayopter states, respectively. In the drawings, F is a focusing plate, C is a condenser lens, P is a pentagram prism, and I is a pupil plane of the finder. Further, G is a first group consisting of a single negative lens. is the second group consisting of a positive single lens, G3 is the third group consisting of a positive single lens, and these three groups G,
, G2, and G3 constitute an eyepiece G. In the illustrated embodiment, the focal length of the second group G2 is F2=4.
6.58, and the focal length F3 of the third group Ga is F. =1
93.83, second group G. The refractive power of the third group G3
It is designed to be stronger. And the first group G, and the third group G. is fixed and the second group G2 is moved on the finder optical axis to adjust the diopter. Aberration diagrams of the first embodiment are shown in FIGS. 4 to 6.

Note that M is a meridional focal line and S is a sagittal focal line. These drawings correspond to Figures 1 to 3, respectively.
It can be seen that aberration correction is good in all cases of 1 day opta, +1 day opta, and -3 day opta. 7 to 9 are optical diagrams of the second embodiment of the present invention, showing the states of -1 dayopter, +1 dayopter, and -3 dayopter, respectively, and the symbols in the drawings are the same as in FIG. 1. The same is true.

In the second embodiment, the second group G. The focal length is F. =57
．． 77, 3rd group G. The focal length of Fa is F3=86.5
1. FIGS. 10 to 12 show aberration diagrams of the second embodiment, and the aberration diagrams are for -1 dayopter, +1 dayopter, and Z-3 dayopter, respectively, and all show that the aberration correction is good. There is. The viewfinder of a single-lens reflex camera with adjustable diopter according to the present invention has the configuration described above, and can obtain a wide diopter adjustment range with a simple configuration. Moreover, Fig. 4 to Fig. 6 and Fig. 10 to
As shown in FIG. 12, since aberrations are well corrected over a wide diopter adjustment range, there is an advantage that visibility is easy and focusing is easy.

Specific numerical examples of the first embodiment 1 and the second embodiment that satisfy the above conditions will be described below.

In the numerical example, PRi is the radius of curvature of the i-th lens surface counted from the object side, D1 is the axial thickness or air spacing of the i-th lens, and Ni and νi are the respective values for the d-line of the i-th lens. These are the refractive index and the Atpe number.

[Brief explanation of the drawing]

Figures 1 to 3 are -1Dp in the first embodiment, respectively.
, +1Dp, and -3Dp, and FIGS. 4 to 6 are optical path diagrams for the states of -1Dp, +1Dp, and +1Dp, respectively, in the first embodiment.
The aberration diagrams in the -3Dp state, FIGS. 7 to 9 are optical path diagrams in the -1Dp, +1Dp, and -3Dp states of the second embodiment, respectively, and FIGS. 10 to 12 are the optical path diagrams in the second embodiment, respectively. It is an aberration diagram of the state of -1Dp, +1Dp, and -3Dp.

Claims (1)

[Claims] 1. In a finder of a single-lens reflex camera in which the diopter is adjusted by moving an eyepiece placed behind the exit surface of a penta roof prism on the finder optical axis, The eyepiece is composed of three groups, sequentially from the penta roof prism side: a first group consisting of a negative single lens, a second group consisting of a positive single lens, and a third group consisting of a positive single lens. When we fix the group and adjust the diopter by moving the second group on the finder optical axis, and let the focal length of the second group be f_2 and the focal length of the third group f_3, (1) f_2 A viewfinder for a single-lens reflex camera with adjustable diopter, characterized in that it satisfies the condition <f_3. 2 The radii of curvature of the second group and the third group are R_9, R_1_0 and R_1_1 from the pentagonal roof prism side, respectively.
, R_1_2, (2) R_9<|R_1_0
(3) A viewfinder for a single-lens reflex camera with adjustable diopter according to claim 1, which satisfies the following conditions: |(3) R_1_1<|R_1_2|.