JPH0423223Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a focus detection optical device.

In the conventional focus detection optical device of a single-lens reflex camera, after the transmitted light of the photographing objective lens forms an image, this light passes through the first and second re-imaging optical elements to form a first image and a second image. There are things that get images. This device has photoelectric converters arranged near the focal planes of the first and second re-imaging optical elements, and the first photoelectric converter on the photoelectric converter that is generated when the imaging objective lens moves in the optical axis direction. Based on the movement of the second image, it is detected whether the projection objective lens is in the in-focus position.

Figures 1 and 2 are diagrams explaining the focus detection optical device of the above-mentioned single-lens reflex camera, where L is the objective lens for photographing, M is the quick return mirror, and S is the lens that is transparent near the optical axis. Focus plate, L ₁
P indicates a reimaging lens (recombination optical element) and a photoelectric converter. Note that the light transmitted through the lens L is guided onto the focus plate S via the quick return mirror M located at the observation position, but for convenience in FIGS. S is arranged and shown. In this device, the light that has passed through the imaging objective lens L is imaged on its focal plane (on the focusing plate S), passes through the transparent part of the focusing plate S, and is re-imaged through a pair of re-imaging lenses _L1 . The image is again formed onto each photoelectric converter P corresponding to each of the imaging lenses _L1 .
Then, the photographing objective lens L is in the optical axis direction (z direction)
, the image formed on each photoelectric converter P moves in the x direction on the surface of this converter P, and the in-focus state of the imaging objective lens can be detected by the output of this converter P. .

Next, the conditions that the focus detection optical system must have will be described. In other words, the focus detection optical system must meet the following conditions: (1) high accuracy in detecting in-focus and out-of-focus conditions; and (2) ability to detect focus even on low-luminance objects.

Regarding condition (1), the opening angle between the optical axis of the re-imaging lens _L1 and the optical axis of the photographing lens L, that is, the first
The larger the angle θ in the figure, the higher the accuracy of focus detection. This means that when the amount of deviation in the optical axis direction of the image position by the photographing lens L with respect to the surface of the focusing plate S (that is, the amount of focus deviation) is the same, the one with a larger angle θ is the first image on the photoelectric converter P and This is because the amount of movement of the second image becomes large. Regarding condition (2), the smaller the F number of the re-imaging lens _L1 , that is, the larger α in Figure 1, the brighter the lens becomes and the larger the output of the photoelectric converter P becomes. However, focus detection is possible.

Next, with reference to FIG. 8, a supplementary explanation will be given of the condition (1) that the focus detection accuracy increases as the angle θ becomes larger.

When the re-imaging lens _L1 is set at an angle θ as shown by the solid line in FIG. If the position is changed, the object image on the photoelectric converter P moves outward by x ₁ on this converter P. On the other hand, if the re-imaging lens L ₁ ' is set at the angle θ' as shown by the broken line in FIG. The subject image moves outward by x ₂ . Therefore, from FIG. 8, it can be seen that when the imaging position of the subject image moves by a certain distance d on the optical axis, the larger the angle θ, the larger the amount of movement of the image on the photoelectric converter P. This means that even if the imaging position of the subject image moves only slightly on the optical axis, this movement can be detected if the angle θ is large, and the larger the angle θ, the higher the focus detection accuracy. It means that.

However, in the conventional device described above, (1) and (2)
It is difficult to satisfy both conditions. In other words, in FIGS. 1 and 2, even the light ray l ₁ that is incident on the most peripheral part of the re-imaging lens L ₁ must come out from the exit pupil of the photographing objective lens L.
The relationship among x, β, and θ must satisfy the following expression β≧α/2+θ. For this purpose, as shown in Figure 1, from the condition (2), the re-imaging lens is
If α is increased to make L ₁ brighter, β is determined by the size of the exit pupil of lens L and the distance from focus plate S, so θ becomes smaller, and condition (1) is sacrificed. . Furthermore, as shown in FIG. 2, if θ is made larger from the condition (1), since β is already determined to be a predetermined value, α becomes smaller, and the condition (2) is sacrificed.

It is an object of the present invention to solve these drawbacks and provide a focus detection optical device that has high focus detection accuracy and is capable of detecting focus even on low-luminance objects.

In the examples shown in FIGS. 3 to 5, the same elements as in the conventional example shown in FIGS. 1 and 2 are given the same symbols.

In the example of Fig. 3, a pair of reimaging lenses L ₂
As shown in FIG. 4, it has a circular shape with one end (outer end) cut off by an arc of a circle centered on the optical axis of the photographing lens L. Also,
The pupil of the re-imaging lens L ₂ is the focal point of the photographing lens L (planned focus) S ₁ , and the exit pupil of the objective lens is symmetrical with respect to S 1.
When projected onto L', it becomes as shown in Figure 5. In other words, the arc portion of the projected image L ₂ ′ is located concentrically with the outer periphery of the exit pupil L′ with a slight spacing therebetween.

The re-imaging lens L ₂ with such conditions is used in the x direction in FIGS. 3 and 5 (the direction perpendicular to the objective lens optical axis within the plane that includes the two optical axes of the re-imaging lens). is larger than the F number in the y direction (direction perpendicular to the surface). In other words, since the angle α of the re-imaging lens L ₂ in the x direction becomes small, even if θ is set large in the cross section in that direction,
As shown in Fig. 3, even the light ray _l1 incident on the edge of the re-imaging lens _L2 is a light ray emerging from the exit pupil of the photographing objective lens L, so the above-mentioned condition (1) cannot be satisfied. can.

On the other hand, in order to satisfy the above-mentioned condition (2), the F number in the y direction must be set in advance to compensate for the decrease in the output of the photoelectric conversion element due to cutting off the reimaging lens _L2 into a crescent shape in the cross section in the x direction. Just keep it small. That is, an increase in the F number of the re-imaging lens _L2 in the x direction can be compensated for by a decrease in the F number in the y direction, thereby suppressing a decrease in output.

However, in the examples of FIGS. 4 and 5, it is not possible to guide the light between the mutually opposing circular portions of the pair of reimaging lenses onto the photoelectric converter.

FIGS. 6 and 7 show an embodiment of the present invention that improves this.

In the embodiment of the present invention shown in FIG. 6, the re-imaging lens L ₃ has a shape in which the mutually opposing portions are substantially parallel and both upper and lower ends are cut off. Re-imaging lens L ₃ in comparison
The F number in the y direction can be made small. Therefore, it is even more advantageous regarding the above-mentioned condition (2).

The overall conditions for determining the aperture angle θ and the F numbers in the x and y directions of the re-imaging lenses L ₂ and L ₃ are as shown in FIGS. 5 and ₇ . When the pupil of L ₃ is projected onto the objective lens exit pupil plane L' point-symmetrically with respect to the focal point S ₁ of the photographing objective lens L, the projected images L ₂ ' and L ₃ ' should not be vignetted.

Therefore, based on the exit pupil size (F number) of the objective lens L determined by the design conditions, determine the F numbers of the re-imaging lenses L ₂ and L ₃ in the x and y directions within a range that does not cause vignetting. There is a need to.

Next, the effects of the above-described embodiment will be described.

In the focus detection device that uses a reimaging lens to form an image on a photoelectric converter as described above, when an image of a point light source (point image) is formed on the focus plate S, photoelectric conversion is performed. A point image is also formed on the device P.
However, in an unfocused state, that is, when a point image is not formed on the focusing plate S, a blurred image with a shape corresponding to the shape of the re-imaging lens is formed on the photoelectric converter P. .

Now, the shape of the pair of re-imaging lenses is semicircular, as shown in the re-imaging lens _L4 shown in FIG.
Assuming that no point image is formed on the focusing plate S, the image on the photoelectric converter P will be semicircular depending on the shape of the reimaging lens _L4 as shown in FIG. Since this type of photoelectric converter P usually uses a light receiving element divided into many parts in the vertical direction in FIG. 10, the outputs of the plurality of light receiving elements forming each photoelectric converter P are compared with each other. However, both outputs will never match each other. That is, as shown in the conceptual diagram of FIG. 11, images of different shapes that do not match each other are compared, and it is difficult to improve the detection accuracy.

In the above-described embodiment of the present invention, the mutually opposing portions of the pair of re-imaging lenses are formed substantially parallel, and the upper and lower ends of each re-imaging lens are cut off so as not to form acute angles. That is, each of the pair of re-imaging lenses has a shape in which the upper and lower ends forming an acute angle of a "semi-circle" are cut off.
Therefore, the pair of reimaging optical elements each have a nearly symmetrical shape, and when superimposed on each other, they almost match. Therefore, it is possible to compare object images having similar shapes compared to the cases of FIGS. 4, 5, and 9. Therefore, focus detection can be achieved with relatively high accuracy even when the subject is out of focus.

Furthermore, even when a field lens is placed at the center of the focusing plate S, the pupil of the re-imaging lens can be adjusted to the exit pupil of the objective lens L by taking into account the effect of refraction by the field lens with respect to the focal point _S1 of the objective lens. If the projected image obtained when projecting in-plane, that is, the image to be projected through the field lens at the S ₁ position, is included in the exit pupil of the objective lens, no vignetting will occur. .

In addition, the photoelectric converter P is accurately connected to the reimaging lens L ₂ ,
Even if it is not placed at the focal position of L ₃ , it is sufficient if it is placed near the focal position.

As described above, according to the present invention, by cutting off the outside of the re-imaging optical element in an arc shape and making the F numbers different in the x and y directions, focus detection accuracy is high and focus detection is possible even at low brightness. An optical device can be obtained. In particular, the outer end of the re-imaging optical element is cut off so that the outer periphery of the projected image of the re-imaging optical element follows the shape of the exit pupil, so a large amount of light is guided to the light receiving element. This is effective in that focus detection can be performed at low brightness. Furthermore, since the shape of each re-imaging optical element is determined to be a shape in which both ends of the re-imaging optical element located perpendicularly to the arrangement direction of each re-imaging optical element are cut off so as not to form an acute angle, Even when the object is out of focus, focus detection can be achieved with relatively high accuracy. Therefore, even if the outer sides of the pair of re-imaging optical elements are cut off in an arc shape as described above, the focus detection accuracy can be increased.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams explaining the conventional example, Figure 3 is an explanatory diagram that is the premise of the present invention, Figure 4 is a diagram showing the re-imaging lens, and Figure 5 is the example of Figure 3. Figures 6 and 7, which are diagrams in which the re-imaging lens is projected onto the exit pupil plane of the imaging objective lens, are examples of the present invention, and are similar to Figures 4 and 5, respectively, and Figure 8. 9 is a diagram illustrating the relationship between the angle θ and focus detection, FIG. 9 is a diagram showing an example of the shape of the re-imaging lens, and FIG. 10 is the shape of the image formed on the photoelectric converter in an out-of-focus state. FIG. 11 is a conceptual diagram illustrating the subject image comparison state of FIG. 10. Explanation of symbols of main parts, L...Objective lens, M
...quick return mirror, S... focus plate,
L ₁ , L ₂ ... Reimaging lens, P ... Photoelectric converter.

Claims (1)

[Claims for Utility Model Registration] Light imaged by a photographic lens is guided to a pair of re-imaging optical elements, and a first image and a second image are formed by the pair of re-imaging optical elements. In addition, a pair of focus detection photoelectric converters are disposed corresponding to the pair of re-imaging optical elements, and a first
In a focus detection device that detects a focusing state of the photographing lens from relative position information of an image and a second image, each pupil of the pair of re-imaging optical elements is set to the photographing lens through a predetermined focal plane of the photographing lens. When projected onto the exit pupil plane of the lens, the pair of projected images projected onto the exit pupil plane are symmetrical with respect to the optical axis of the photographing lens and are located within a circular exit pupil centered on the optical axis. and an outer periphery of the pair of projected images remote from the optical axis coincides with a circle centered on the optical axis of the photographic lens, and portions of the pair of projected images that face each other in the alignment direction are substantially parallel to each other. and further, the F-number of each re-imaging optical element in the arrangement direction of the pair of re-imaging optical elements is larger than the F-number of each re-imaging optical element in the direction perpendicular to the arrangement direction. The shape of the pair of re-imaging optical elements is determined, and each of the pair of re-imaging optical elements has a shape in which both ends located in the perpendicular direction are cut off so as not to form an acute angle. Focus detection optical device.