JPS6054648B2 - Diopter adjustable viewfinder optical system - Google Patents

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 that adjusts the diopter by moving a part of the eyepiece in the direction of the finder optical axis.

Generally, a subject image in a finder optical system of a single-lens reflex camera is observed by focusing the subject image on a pit plate through a pentagonal roof prism at a position of about -1 diopter with an eyepiece.

However, if the observer is severely myopic or farsighted, or has weak diopter adjustment ability, it will be difficult to observe the object image formed around -1 dayopter with the naked eye. For this reason, in the finder optical system of conventional single-lens reflex cameras, an attachment lens was attached to the rear of the eyepiece lens to adjust the diopter. However, it has not been possible to continuously adjust the diopter, and the eye point position for observation has become 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 optical axis.

The diopter change ΔDp at this time is f
e (77Z7Jl), the amount of movement on the finder optical axis is Δ
If S(Tfrfn), ΔDp■1000・ΔS/f
It is expressed as e2.

In the case of a 357m version single-lens reflex camera, the focal length of the eyepiece is approximately 6' based on the optical path length of the pentagonal roof prism provided between the eyepiece and the pit plate.

For this reason, in order to provide a predetermined change in diopter, the eyepiece lens must be moved significantly, which requires a large space behind the pentagonal roof prism, and is difficult to realize in a small single-lens reflex camera. For example, to give a diopter change of ±1 dayopter, the eyepiece should be adjusted to about 7wrm.
It has to be moved. As a method of reducing the amount of movement of the eyepiece, several proposals have been made in Japanese Patent Application Laid-open Nos. 55-67732 and 1982-126531. In these proposals, the eyepiece is constructed from a single lens with negative refractive power and a single lens with positive refractive power from the penta roof prism side, one of which is fixed and the other is moved along the viewfinder optical axis to adjust the diopter. I'm going. 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 performance of the finder observed image cannot be said to be fully satisfactory. Also, more space is required to move the movable lens, the eyepoint position becomes shorter because the rear part of the eyepiece protrudes toward the eyepoint, and the eyepiece must be made larger to secure the eyepoint position. However, it had some drawbacks. The present invention includes an eyepiece lens with adjustable diopter.
The object of the present invention is to obtain a finder optical system in which the eye point position, which is not well corrected for aberrations, is lengthened.

The feature of the structure of the present invention is that the eyepiece lens is composed of three 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 viewfinder. The problem lies in the fact that we are making adjustments.

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

1 to 3 are schematic diagrams of a part of the finder optical system according to the first embodiment of the present invention, and FIGS. 7 to 9 are schematic diagrams of a part of the finder optical system according to the second embodiment of the present invention. . In the figure, 1 is a focusing plate, 2 is a condenser lens, 3 is a block with a penta roof prism, 4 is a first lens group with negative refractive power, 5 is a second lens group with negative refractive power, 6
is a third lens group with positive refractive power, and 7 is an eye point.

The eyepiece lens consists of a first lens group 4, a second lens group 5, and a third lens group 6. The eyepiece in this embodiment fixes the first lens group and the third lens group, and adjusts the diopter by moving the second lens group on the viewfinder optical axis. At this time, the focal point of the first lens group distance f1,
A finder optical system is achieved that satisfies the conditions for the focal length F2 of the second lens group and performs good aberration correction even when the diopter changes.

The eyepiece of a conventional finder optical system is composed of two lens groups: the first lens group with negative refractive power and the second lens group with positive refractive power, which tends to shorten the eyepoint position and furthermore Many aberrations occurred in one lens group, especially spherical aberration in the positive diopter, which degraded the performance of the finder image.

The eyepiece according to the present invention has a first lens group with a fixed negative refractive power disposed on the side of the penta-roof prism, thereby reducing the inclination angle of off-axis rays and moving away the position where they intersect with the optical axis, thereby changing the eye point position to the pentagonal roof prism. It lasts longer than a roof prism.

At this time, the relationship between the refractive powers of the negative lenses of the first lens group and the second lens group is changed by making the refractive power of the second lens stronger than that of the first lens group, that is, as shown in conditional expression (1), Ifll> By providing 1f21, the distance between the principal points of the negative lens group and the positive lens group is prevented from becoming excessively wide, the focal length of the eyepiece is lengthened, and the viewfinder magnification is prevented from decreasing, and an asymmetrical difference is prevented from occurring. There is. Although the object of the present invention can be achieved with the above configuration, in order to better correct various aberrations of the eyepiece lens, the radius of curvature of each lens surface of the first lens group and the second lens group is adjusted sequentially from the penta roof prism side. It is preferable to satisfy the conditional expression when R7, R8, R9, and RlO.

Conditional expressions (2) and (3) change the shapes of the negative lenses of the first lens group and the second lens group determined under conditional expression (1) to shapes that strengthen the lens surface on the eye point side. By doing so, off-axis aberrations are reduced and corrected to improve observation of the finder image.

If either conditional expression (2) or conditional expression (3) is violated, off-axis aberrations will not be corrected well and a good finder image will not be obtained.

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

FIGS. 1, 2, and 3 are schematic diagrams of the optical system of Example 1 of the present invention, and show the states of the optical system at -1 dayopter, -3 dayopter, and +1 dayopter, respectively.

Various aberrations at this time are shown in FIG. 4, FIG. 5, and FIG. 6 in order. In Example 1, the focal length f1 of the first lens group is f1
=-85. The focal length F2 of the second lens group is F2=-72.80, which is 1f11>]F2l. 7, 8, and 9 are schematic diagrams of the optical system of Example 2 of the present invention, which are -1 dayopter, -3 dayopter, and +1 dayopter, respectively.
Shows the state of the optical system when using a diopter.

Various aberrations at this time are shown in FIG. 10, FIG. 11, and FIG. 12 in order. In Example 2, the focal length f1 of the first lens group
is f1=-72.47, and the focal length F2 of the second lens group is F2=-56.28, which is 1f1! 〉1f21. 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, aberrations can be well corrected over a wide diopter adjustment range and the eye point position can be made long. A finder optical system for a single-lens reflex camera can be obtained.

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

In the numerical examples, R1 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 νi are respectively calculated from the left side in the figure. These are the refractive index and Atsube number of the first optical member counted from the center left side.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are -1 of Embodiment 1 of the present invention, respectively.
A schematic diagram of a part of the finder optical system in Dp1-3Dp1+1Dp, FIGS. 4, 5, and 6 are diagrams of various aberrations in -1Dp1-31)p1+IDP, FIG. 8 and 9 are schematic diagrams of a part of the finder optical system in -1Dp1-3DP1+1Dp of Example 2 of the present invention, FIG. 10, FIG. 11, and FIG.
Figure 2 shows -1Dp1-3Dp1 of Example 2 of the present invention, respectively.
It is a diagram of various aberrations at +1Dp. In the figure, 1 is a focusing plate, 2 is a condenser lens, 3 is a block with a penta roof prism, 4 is the first lens group, 5 is the second lens group, 6 is the third lens group, 7 is the eye point, and M is the eye point. Merideona 5 focal line, S is sagittal focal line.

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 optical axis, the eyepiece lens has a negative refractive power from the penta roof prism side. It has a first lens group, a second lens group with negative refractive power, and a third lens group with positive refractive power, the focal length of the first lens group is f_1, and the focal length of the second lens group is f_2. , when the condition |f_1|>|f_2| is satisfied,
A finder optical system capable of adjusting diopter, characterized in that the first lens group and the third lens group are fixed, and the diopter is adjusted by moving the second lens group on the finder optical axis. 2 The radius of curvature of the lens surfaces of the first lens group and the second lens group is set as R_7 and R in order from the penta-roof prism side.
When _8, R_9, R_1_0, R_7>R_8
The finder optical system with adjustable diopter according to claim 1, characterized in that the condition R_9>R_1_0 is satisfied.