JPH09189868A - Finder optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain observation magnification and eye relief having specified length and to observe an excellent finder image by moving a lens on an optical axis, changing the observation magnification and adjusting visibility. SOLUTION: In the case of observing an object image formed on a specified surface by a photographing lens 1, a 1st group L1 having positive refractive power, a 2nd group L2 having negative refractive power and a 3rd group L3 having positive refractive power are arranged in order from the specified surface side. By moving the 1st group L1 on the optical axis from an eye point 8 side to a focusing screen 3 side, variable power is performed. Then, the 2nd group L2 is moved on the optical axis along a locus facing a convex surface on the focusing screen 3 side so as to adjust eyesight. The eyesight adjustment of a finder caused by the difference of an observer is performed by moving the 3rd group L3 on the optical axis. Thus, the eyesight of the finder is kept nearly constant and an excellent finder image where aberration is excellently corrected is observed though the observation magnification is very largely changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system, and in particular, it has a function of changing an observation magnification and a diopter at the same time, thereby making it possible to appropriately meet the demand of an observer, for example, a single-lens reflex camera. The present invention relates to a finder optical system suitable for the above.

[0002]

2. Description of the Related Art Conventionally, in a single-lens reflex camera, a subject image formed by a taking lens is reflected by a quick return mirror arranged on the image plane side of the taking lens and formed on a focusing screen, and the subject image on the focusing screen is formed. It is configured so that an erect image is formed through a pentaprism or the like and then magnified and observed by a finder optical system. For the observer, the subject image observed from the finder optical system becomes easier to see as the observation magnification is higher, and the maximum distance from the exit surface of the finder optical system to the position where the subject image can be observed without being shaken. The larger the distance (which will be referred to as eye relief) is set, the easier it becomes to see. In order to solve these two propositions at the same time, the optical path length of an optical system for forming an erect image such as a pentaprism may be shortened.

However, it is also necessary to satisfy the conditions such as satisfying a predetermined viewfinder field ratio and removing harmful light such as ghost. For this reason, it is very difficult to solve these two propositions at the same time because an optical path length is actually required to some extent. Generally, when the optical path length of the optical system for forming an erect image is fixed, the eye relief becomes short when trying to increase the observation magnification, and the eye magnification becomes low when trying to lengthen the eye relief. It has a relationship of being lost.

A viewfinder optical system of a single-lens reflex camera having a variable observation magnification is provided, for example, in order to make it possible to select either a high magnification or a long eye relief depending on the observer's intention. It is proposed in Japanese Patent Publication.

On the other hand, it is generally known that, when an object image is observed using an optical device such as a single-lens reflex camera, the observer usually comes into a myopic state called mechanical myopia. Therefore, in viewfinder optical systems of many single-lens reflex cameras, in consideration of this, the diopter is configured to be in the vicinity of −1 diopter. However, the diopter that is easy for the observer to see is different for each observer.

[0006] For example, when it is used both for everyday use by a person who wears glasses while observing while wearing the glasses and when observing without using the glasses, it is desirable that the diopter of the finder can be greatly changed. . When a person with weak diopter adjustment ability observes, it is desirable that the diopter of the finder can be finely adjusted.

A finder optical system of a single-lens reflex camera capable of appropriately adjusting the diopter of the finder according to the observer's will has been proposed in, for example, Japanese Patent Publication No. 60-48730.

[0008]

In the viewfinder optical system of a single-lens reflex camera, it is very convenient for the observer to make the observation magnification, or the eye relief length and the viewfinder diopter, variable. However, if it is attempted to achieve each of these functions with a single finder optical system, the entire optical system becomes complicated and it becomes very difficult to exhibit each function well.

According to the present invention, when observing a subject image (finder image) formed on a predetermined surface by a photographing lens, each element is appropriately set to reduce the size of the entire optical system, and a predetermined observation magnification and Finder optics suitable for single-lens reflex cameras, etc. that can easily obtain eye relief of a predetermined length and can easily meet the demands of the observer who can easily adjust the diopter and can observe a good finder image. The purpose is to provide the system.

[0010]

The finder optical system of the present invention comprises a first lens group having a positive refractive power and a negative refractive power in order from the predetermined surface side when observing an object image formed on the predetermined surface by a taking lens. The three lens groups of the second lens group of power and the third lens group of positive refractive power are arranged, and the first lens group or the first lens group and the second lens group are moved on the optical axis to change the observation magnification. It is characterized in that the third group is moved on the optical axis to adjust the diopter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of an essential part when a finder optical system of Numerical Embodiment 1 of the present invention, which will be described later, is applied to a single-lens reflex camera, and FIG. 2 is a partial view including a pentaprism 5 of FIG. It is a principal part schematic diagram when the optical path of an optical element is expanded.

FIGS. 3A, 3B and 3C are aberration diagrams when the observation magnification of the finder optical system of Numerical Example 1 is changed, and FIGS. 2A, 2B and 2C, respectively. It corresponds to (C). 4A, 4B, and 4C are explanatory diagrams of diopter adjustment of the finder optical system of Numerical Example 1. FIG.
4A, 4B, and 4C are aberration diagrams when the diopter adjustment of the finder optical system of Numerical Example 1 is performed, and correspond to FIGS. 4A, 4B, and 4C, respectively. doing.

In FIG. 1, 1 is a taking lens, 2 is a quick return mirror, 3 is a focusing screen, and the taking lens 1
The viewfinder image is formed by. Reference numeral 4 is a condenser lens, 5 is a pentaprism, and the viewfinder image on the focusing screen 3 is an erect image. Reference numeral 6 denotes a finder optical system which also serves as an eyepiece. Reference numeral 7 indicates the protective glass, and 8 indicates the position of the eye point.

The finder optical system 6 has a positive refractive power of the first
It has three lens groups, a group L1, a second group L2 having a negative refractive power, and a third group L3 having a positive refractive power.

In FIG. 2, (A) shows when the observing magnification and eye relief of the finder optical system 6 are standard,
In (B), the observing magnification of the finder optical system 6 is high and the eye relief is slightly short, and in (C), the observing magnification of the finder optical system 6 is slightly low and the eye relief is slightly long. It represents each time.

The finder optical system 6 is shown in FIG.
As shown in (C), when the observation magnification is changed from the low magnification side to the high magnification side, the first group L1 is moved to the eye point 8 as shown by the arrow.
Side to the focusing screen 3 side to monotonously move on the optical axis to change the magnification, and accordingly, the second lens unit L2 is moved on the optical axis along the locus with the convex surface facing the focusing screen 3 side to obtain diopter. I am adjusting.
The diopter adjustment depending on the observer of the finder is carried out by moving the third lens unit L3 on the optical axis as shown in FIG.

FIG. 4A shows the case where the observation magnification and the eye relief are standard respectively, and when the diopter of the finder is around the standard -1 diopter, FIG. 4B shows the same observation magnification. 4C shows an eye magnification and an eye relief in the vicinity of −3 diopters, and FIG. 4C shows a similar observation magnification and eye relief in the vicinity of +1 diopters.

In the present embodiment, the third lens unit L3 is moved to the eyepoint 8 side in order to change from-diopter (for example, -3dpt in FIG. 4B) to + diopter (for example, + 1dpt in FIG. 4C). I am letting you.

In the present embodiment, the finder optical system 6 is constructed as described above to simultaneously have the function of changing the observing magnification and diopter of the finder, so that the observer's request can be appropriately met. In particular, keeping the diopter of the viewfinder substantially constant while changing the observation magnification sufficiently large,
Moreover, a finder optical system capable of observing a good finder image in which various aberrations are well corrected is achieved.

In this embodiment, it is preferable to satisfy the following conditions in order to observe a good finder image over the entire observation magnification.

When the focal length of the i-th group is fi and the diopter of the entire system is -1 diopter, the focal lengths of the entire system at the maximum and minimum viewing magnifications are fT and fW, respectively.

[0022]

[Equation 2] Satisfying the following conditions.

Conditional expressions (1) to (3) are observed with respect to the combined focal lengths of the first to third groups when the diopter of the entire finder optical system is set to the standard diopter (-1 diopter). The value at the maximum magnification is fT, and the value at the minimum observation magnification is fW. Then, using the intermediate observation magnification as the standard observation magnification, the focal lengths of the entire finder optical system from the first group to the third group at this time are calculated, and the first group, the second group, and the third group are calculated.
It defines the ratio to the focal length of each of the groups.

With these conditional expressions, various aberrations are favorably corrected with a compact structure as a viewfinder optical system of a single-lens reflex camera, and the amount of movement of the lens group for zooming the observation magnification and adjusting the viewfinder diopter is too large. The refractive power arrangement is defined so as not to become.

If the focal length of the first lens unit becomes short beyond the lower limit value of the conditional expression (1), the total length of the optical system becomes short, but it becomes difficult to correct various aberrations instead. On the contrary, when the focal length of the first lens unit becomes long beyond the upper limit of conditional expression (1), it becomes easy to correct various aberrations, but the total length of the optical system becomes long. If the lower limit of conditional expression (2) is exceeded and the focal length of the second lens unit becomes short, the total length of the optical system becomes short, but it becomes difficult to correct various aberrations.

On the contrary, when the focal length of the second lens unit becomes long beyond the upper limit of the conditional expression (2), it becomes easy to correct various aberrations but the total length of the optical system becomes long. The first group and the second group are lens groups that change the observation magnification while keeping the diopter of the finder constant by moving on the optical axis while changing the distance between them. In order to correct the occurrence of various aberrations to a sufficiently small value while sufficiently reducing the amount of movement of the lens group, it is desirable that the above conditional expressions (1) and (2) be satisfied.

Further, when the focal length of the third lens unit becomes short beyond the lower limit value of the conditional expression (3), there is an advantage that the moving amount of the lens unit for diopter adjustment can be reduced, but instead, various aberrations occur. Is difficult to correct. On the other hand, if the focal length of the third lens unit becomes long beyond the upper limit of conditional expression (3), it becomes easy to correct various aberrations, but the amount of movement of the lens unit for adjusting diopter increases, which is not preferable. Further, if the focal length of the third lens unit is set beyond the range defined by the conditional expression (3), the ratio of the focal lengths of the first lens unit and the second lens unit becomes inadequate, and various factors during zooming of the observation magnification are obtained. It becomes difficult to satisfactorily correct the occurrence of aberration.

The finder optical system of the present invention has the above-mentioned 3
The focal lengths of the lens groups are set so as to satisfy the two conditional expressions (1) to (3), and a lens system having an appropriate refractive power arrangement is provided, and then each lens group is moved to the optical system as described above. The on-axis movement has a feature that various aberrations can be favorably corrected while realizing a particularly compact structure.

Further, in the present invention, when the focal lengths of the respective lens groups are respectively set so that the numerical ranges of the above-mentioned three conditional expressions are further defined by the following numerical ranges, it can be realized better.

[0030]

(Equation 3) In the present invention, the first group is further configured to have at least two positive lenses, and the first group is moved from the low magnification side to the high magnification side on the optical axis from the eye point side to the focusing screen side. By moving the lens, better optical characteristics are obtained.

In the present invention, the first lens group is a main variable power lens group for changing the observation magnification of the finder,
It is required to have a sufficiently large zooming effect with a small amount of lens movement and to correct the occurrence and fluctuation of various aberrations to a sufficiently small level. Therefore, the two positive lenses are configured to share the positive refracting power. And the first of this positive refractive power
By moving the lens group from the low-power side to the high-power side on the optical axis from the eye point side to the reticle side, a sufficiently large zooming effect is realized with a small amount of movement.

Further, in the present invention, it is more preferable that the first lens group further has at least one negative lens, whereby various aberrations generated in the first lens group, particularly chromatic aberration of magnification, can be improved. After correction, a finder optical system suitable for a better single-lens reflex camera is realized.

In the present invention, the second group constituting the finder optical system is composed of a single negative lens whose both lens surfaces are concave, and the third group is a meniscus-shaped single lens with the convex surface facing the focusing screen side. It is composed of a positive lens, and thereby, the optical system as a whole is downsized and good optical performance is obtained.

Next, numerical examples of the finder optical system of the present invention will be shown based on the optical system shown in FIG. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the reticle side, Di is the i-th lens thickness and air gap from the reticle side, and Ni and νi are the i-th in order from the reticle side, respectively. It is the refractive index and Abbe number of the lens glass.

Further, the calculation results of the finder magnification and the eye relief when the finder optical system of each numerical example is realized will be shown. Finder magnification has a focal length of 50 m
It can be represented by the angular magnification of the afocal system when the standard lens of m is attached as a photographic lens, and here it is approximately represented by the ratio of the focal length of the photographic lens and the focal length of the finder optical system.

On the other hand, the eye relief is strictly determined by the effective dimensions of the optical components that make up the finder optical system, and tends to become shorter as the optical components are made smaller. It is assumed that the exit surface of the prism 5 is configured to regulate the eye relief, the diameter of the effective light beam on this surface is φ23 mm, and the light beam emitted from the point of the object height h = 20 mm on the focal plane of the focusing screen 3. Of these, the position where a light ray having a light ray height h = 11.5 mm on the exit surface of the pentaprism 5 (the fourth surface of the numerical example) passes through the finder optical system 6 and the protective glass 7 and intersects with the finder optical axis is calculated. However, the distance from the exit surface of the protective glass 7 to this point is represented as an approximate eye relief. (Numerical Example 1) R 1 = ∞ D 1 = 4.7 N 1 = 1.51633 ν 1 = 64.2 R 2 = −68.80 D 2 = 1.0 R 3 = ∞ D 3 = 86.0 N 2 = 1.51633 ν 2 = 64.2 R 4 = ∞ D 4 = Variable R 5 = -168.27 D 5 = 1.3 N 3 = 1.76182 ν 3 = 26.5 R 6 = 114.58 D 6 = 4.2 N 4 = 1.77250 ν 4 = 49.6 R 7 = -58.00 D 7 = 0.2 R 8 = 56.53 D 8 = 3.3 N 5 = 1.77250 ν 5 = 49.6 R 9 = -316.45 D 9 = variable R10 = -129.46 D10 = 1.2 N 6 = 1.83400 ν 4 = 37.2 R11 = 23.50 D11 = variable R12 = 23.74 D12 = 3.4 N 7 = 1.80400 ν 5 = 46.6 R13 = 96.85 D13 = Variable R14 = ∞ D14 = 1.2 N 8 = 1.51633 ν 5 = 64.2 R15 = ∞ <Interval change during zooming><Distance change during diopter adjustment> Variable Interval Normal High Magnification Low Magnification Variable Interval Normal (-1dpt) -3dpt + 1dpt D4 4.7 1.0 7.5 D4 4.7 4.7 4.7 D9 3.5 6.6 1.0 D9 3.5 3.5 3.5 D11 4.5 5.1 4.2 D11 4.5 1.7 7.5 D13 4.0 4.0 4.0 D13 4.0 7.3 1.0 Capacitor Distance from lens to reticle ... 0.6 <Change of observation magnification (when 50mm shooting lens is attached) and eye relief at magnification> Observation magnification Eye relief passage normally 0.68 times 20.2mm high magnification 0.73 × 13.4mm low magnification 0.63 × 26.1mm

[0037]

(Equation 4) (Numerical Example 2) R 1 = ∞ D 1 = 4.7 N 1 = 1.51633 ν 1 = 64.2 R 2 = −70.33 D 2 = 1.0 R 3 = ∞ D 3 = 86.0 N 2 = 1.51633 ν 2 = 64.2 R 4 = ∞ D 4 = Variable R 5 = -147.29 D 5 = 1.3 N 3 = 1.76182 ν 3 = 26.5 R 6 = 461.09 D 6 = 4.0 N 4 = 1.69680 ν 4 = 55.5 R 7 = -50.05 D 7 = 0.2 R 8 = 47.72 D 8 = 3.8 N 5 = 1.69680 ν 5 = 55.5 R 9 = -405.80 D 9 = Variable R10 = -108.70 D10 = 1.2 N 6 = 1.83400 ν 4 = 37.2 R11 = 25.35 D11 = Variable R12 = 24.45 D12 = 3.6 N 7 = 1.69680 ν 5 = 55.5 R13 = 174.28 D13 = Variable R14 = ∞ D14 = 1.2 N 8 = 1.51633 ν 5 = 64.2 R15 = ∞ <Interval change during zooming><Distance change during diopter adjustment> Variable Interval Normal High Magnification Low Magnification Variable Interval Normal (-1dpt) -3dpt + 1dpt D4 4.7 1.0 7.5 D4 4.7 4.7 4.7 D9 3.5 6.6 1.0 D9 3.5 3.5 3.5 D11 4.5 5.1 4.2 D11 4.5 1.4 7.8 D13 4.3 4.3 4.3 D13 4.3 7.4 1.0 Capacitor Distance from lens to reticle ... 0.6 <Change of observation magnification (when 50mm shooting lens is attached) and eye relief at magnification change> Observation magnification Eye relief passage normally 0.68 times 19.1mm high magnification 0.73 × 12.2mm low magnification 0.63 × 25.0mm

[0038]

(Equation 5) (Numerical Example 3) R 1 = ∞ D 1 = 4.7 N 1 = 1.51633 ν 1 = 64.2 R 2 = -66.85 D 2 = 1.0 R 3 = ∞ D 3 = 86.0 N 2 = 1.51633 ν 2 = 64.2 R 4 = ∞ D 4 = Variable R 5 = -116.26 D 5 = 2.8 N 3 = 1.77250 ν 3 = 49.6 R 6 = -52.30 D 6 = 0.2 R 7 = 61.56 D 7 = 3.5 N 4 = 1.77250 ν 4 = 49.6 R 8 = -182.03 D 8 = variable R 9 = -91.82 D 9 = 1.2 N 5 = 1.83400 ν 5 = 37.2 R10 = 23.41 D10 = variable R11 = 23.95 D11 = 3.4 N 6 = 1.80400 ν 4 = 46.6 R12 = 149.47 D12 = variable R13 = ∞ D13 = 1.2 N 7 = 1.51633 ν 5 = 64.2 R14 = ∞ <Interval change during zoom><Distance change during diopter adjustment> Variable interval Normal High magnification Low magnification Variable interval Normal (-1dpt)- 3dpt + 1dpt D4 4.7 1.0 7.5 D4 4.7 4.7 4.7 D8 3.5 6.7 1.0 D8 3.5 3.5 3.5 D10 4.5 5.0 4.2 D10 4.5 2.1 7.0 D12 3.5 3.5 3.5 D12 3.5 5.9 1.0 Distance from condenser lens to reticle 0.6 0.6 Observation magnification at the time of double (when 50mm shooting lens is attached) and eye relief change> Observation magnification Eye relief Normally 0.68 times 21.8mm High magnification 0.73 times 14.4mm Low magnification 0.63 times 28.1mm

[0039]

(Equation 6)

[0040]

As described above, according to the present invention, when observing a subject image (finder image) formed on a predetermined surface by the taking lens, the respective elements are appropriately set to reduce the size of the entire optical system. While aiming, it is possible to easily obtain an eye relief with a predetermined observation magnification and a predetermined length, and it is possible to appropriately meet the demands of the observer who can easily adjust the diopter, and also to observe a good viewfinder image. A finder optical system suitable for a reflex camera or the like can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of essential parts when a finder optical system according to Numerical Example 1 of the present invention is applied to a single-lens reflex camera.

FIG. 2 is a cross-sectional view of essential parts when an optical path of a part of FIG. 1 is expanded.

FIG. 3 is an aberration diagram when the observation magnification of Numerical Example 1 of the present invention is changed.

FIG. 4 is an explanatory diagram of diopter adjustment according to Numerical Example 1 of the present invention.

FIG. 5 is an aberration diagram when the diopter of Numerical Example 1 of the present invention is changed.

FIG. 6 is a cross-sectional view of essential parts when an optical path of a numerical example 2 of the present invention is expanded.

FIG. 7 is an aberration diagram when the observation magnification of Numerical Example 2 of the present invention is changed.

FIG. 8 is an explanatory diagram of diopter adjustment according to Numerical Example 2 of the present invention.

FIG. 9 is an aberration diagram when the diopter of Numerical Example 2 of the present invention is changed.

FIG. 10 is a cross-sectional view of essential parts when an optical path of Numerical Example 3 of the present invention is expanded.

FIG. 11 is an aberration diagram when changing the observation magnification in Numerical Example 3 of the present invention.

FIG. 12 is an explanatory diagram of diopter adjustment according to Numerical Example 3 of the present invention.

FIG. 13 is an aberration diagram when the diopter of Numerical Example 3 of the present invention is changed.

[Explanation of Codes] 1 Photographic lens 2 Quick return mirror 3 Focus plate 4 Condenser lens 5 Penta prism 6 Viewfinder optical system 7 Protective glass 8 Eyepoint L1 1st group L2 2nd group L3 3rd group d d line ΔS sagittal image plane ΔM meridional image plane

Claims (4)

[Claims] 1. When observing an object image formed on a predetermined surface by a taking lens, a first lens having a positive refractive power is sequentially provided from the predetermined surface side.
A first lens group, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, and the first lens group or the first lens group and the second lens group.
A finder optical system characterized in that the group is moved on the optical axis to change the observation magnification, and the third group is moved on the optical axis to adjust the diopter. 2. The focal lengths of the entire system at the maximum and minimum observation magnifications when the focal length of the i-th group is fi and the diopter of the entire system is −1 diopter are fT and fW, respectively. When you do [Equation 1] The finder optical system according to claim 1, which satisfies the following condition. 3. The first group has at least two positive lenses, and is moved along the optical axis to the predetermined surface side when changing the observation magnification from low magnification to high magnification. The finder optical system according to claim 1 or 2. 4. The first group includes at least one negative lens and at least two positive lenses, and when the observation magnification is changed from low magnification to high magnification, the optical axis moves toward the predetermined surface side. The finder optical system according to claim 1 or 2, wherein the finder optical system is moved upward.