JPS6233564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device, and more particularly to a so-called TTL focus detection device suitable for optical equipment such as a single-lens reflex camera.

Various so-called TTL focus detection devices applied to optical equipment such as single-lens reflex cameras have been proposed in the past. By the way, among these conventional proposals, for example, the light of the photographic optical system is placed substantially behind the planned focal plane (plane equivalent to the film surface) of the photographic optical system that is to be focused on the subject. Two imaging lenses are juxtaposed symmetrically with respect to an axis, and an image of a subject formed by the photographing optical system is adjusted by the two imaging lenses according to a change in position on the axis. The imaging position of each image to be formed is relatively changed in a direction substantially perpendicular to the optical axis of each imaging lens, and the imaging position of two images to be formed by the two imaging lenses is For example, a focus detection device for a single-lens reflex camera, which detects the focus adjustment state of the above-mentioned photographic optical system with respect to the subject by detecting relative changes in the subject using a photoelectric detector, is disclosed in Japanese Patent Application Laid-Open No. Although proposed in Japanese Patent No. 52-138924, the focus detection device according to this proposal does not evaluate the degree of blurring of the image formed by the imaging optical system, that is, the image clarity; The change in the position of the image formed by the imaging optical system on the optical axis is replaced by a relative change in the imaging position of the two images formed by the two imaging means. Since it detects this, various practical difficulties found in the so-called image sharpness detection type device mentioned above are solved, and compared to this kind of image sharpness detection type device, Focus detection with relatively high accuracy can be expected, and in addition, the directionality in the case of out-of-focus, that is, whether it is front focus or back focus, can be easily distinguished, which is very advantageous.

However, even with this type of device, in order to put it into practical use, it must be incorporated into a device such as a single-lens reflex camera so that its full functionality can be demonstrated. There are still many points that need to be improved. For example, in the device according to the conventional proposal listed above, the two imaging lenses described above are simply arranged side by side behind the planned focal plane of the photographing optical system, with their optical axes sandwiched between them. However, in the arrangement of such a detection optical system, the incident light flux to each of the two imaging lenses is always the same as that of the photographing optical system.
Since it is not possible to limit the light beams to be emitted from relatively the same position, it is not always possible to guarantee the identity of the two images formed by each of the two imaging lenses. Therefore, there is a problem in that the detection accuracy cannot always be sufficiently guaranteed when detecting a relative change in the imaging position of the two images by the photoelectric detector. In addition to this, regarding the arrangement of the detection optical system,
Since the change in the angle of view of the photographing optical system has a large effect on the two images formed by the two imaging lenses, detection accuracy is likely to deteriorate in this respect as well.
Furthermore, there are problems such as vignetting of the light beam or a decrease in the amount of light caused by the two imaging lenses, which makes it even more difficult to maintain detection accuracy.

The present invention has been made in view of the above points, and is a TTL focus detection device of the type that detects a relative change in the imaging position of two images as described above, that is, with respect to an object. an image of the object formed by the main imaging optical system behind the intended focal plane of the main imaging optical system to be focused;
a second imaging optical system that forms two images in a relationship such that each imaging position changes relatively in accordance with a change in position on the optical axis; A conventional focus detection device detects the focusing state of the main imaging optical system with respect to the object by detecting a relative change in the imaging position of the two images focused by the system. By eliminating all the above-mentioned disadvantages in the proposed configuration, it is possible to sufficiently guarantee the identity of the two images formed by the second imaging optical system, and the second
The influence of changes in the angle of view of the main imaging optical system on the two images formed by the second imaging optical system can be almost completely eliminated, and furthermore, the influence of the change in the angle of view of the main imaging optical system on the two images formed by the second imaging optical system can be almost completely eliminated. Problems such as vignetting or reduction in light intensity can be more advantageously avoided, and overall, the accuracy of detection of the relative change in the imaging position of the two images by the photoelectric detection means can be improved, and therefore the main result can be improved. image optical system,
The purpose of the present invention is to provide a more advantageous and improved arrangement configuration of a detection optical system that can further improve the detection accuracy of the focus adjustment state with respect to an object.
The feature is that in the configuration of the device described above, a third imaging optical system is disposed at least in the vicinity of the planned focal plane of the main imaging optical system, and at this time, the third imaging optical system The second imaging optical system is arranged so that the pupil plane of the second imaging optical system is in a substantially conjugate relationship with the pupil plane of the main imaging optical system.

Further, according to the present invention, as an improvement to the optical arrangement described above, a fourth imaging optical system is provided between the third imaging optical system and the second imaging optical system. , with its focal point substantially coinciding with the planned focal plane of the main imaging optical system, and at this time, the third and fourth imaging optical systems are used to align the focal plane of the second imaging optical system. An arrangement of a focus detection optical system is proposed in which the pupil plane is placed in a substantially conjugate relationship with the predetermined focal plane of the main imaging optical system. , ensuring the identity of the two images formed by the second imaging optical system, eliminating the effects caused by changes in the angle of view of the main imaging optical system, and solving problems such as vignetting of the light beam or reduction in the amount of light. In addition to the effects of eliminating the above, it also maintains the same illuminance of the two images, eliminates the disadvantage that the separation distance between the image points of the two images increases significantly, and optically positions each element constituting the detection system. In addition, effects such as simplification of adjustment can be obtained.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First of all, FIG. 1 shows the principle arrangement of the optical system in an embodiment of the present invention, in which numeral 1 indicates an object to be focused (in terms of a camera, the subject), and numeral 2 indicates an image of the object 1. The main imaging optical system (in terms of a camera, it is a photographing lens - hereinafter simply referred to as imaging) is adjustable along its optical axis 0 in order to focus on the planned focal plane F (in terms of a camera, the plane equivalent to the film surface). 3 is a second imaging optical system for forming two images, which is disposed behind the expected focal plane F of the imaging lens 2, as shown in the figure. It includes two relay lenses 3A and 3B arranged symmetrically with respect to optical axis 0. Reference numeral 4 denotes a third imaging optical system (hereinafter referred to as field optical system) disposed to substantially coincide with the planned focal plane F of the imaging lens 2.
5 is the above-mentioned relay lens 3
A photoelectric detection means provided for the purpose of detecting a relative change in the imaging position of the two images formed by the imaging lenses 2 and 3B.
is focused on the object 1, two photoelectric detectors are positioned in advance so that the images formed by the relay lenses 3A and 3B are received at approximately the center of the respective photoelectric detection surfaces. Detectors 5A and 5B
It includes.

In the arrangement of the optical system shown in FIG.
are placed in a conjugate relationship with each other, and the expected focal plane F of the imaging lens 2 (field lens 4 surface)
and the detection surfaces of the photoelectric detectors 5A and 5B are in a conjugate relationship with each other through the relay lenses 3A and 3B, respectively, that is, each detection surface of the photoelectric detectors 5A and 5B It is set so that it becomes a secondary imaging surface when it is defined as a primary imaging surface.

In the arrangement of such an optical system, first, the image Ii of the object 1 is formed near the field lens 4 by the imaging lens 2, and then this image Ii is transmitted to the relay lenses 3A and 3B. Photoelectric detector 5A,
It began to be re-imaged on 5B, and at this time,
Images Ia and Ib formed on the photoelectric detectors 5A and 5B
are the pupil plane of the imaging lens 2 and the relay lens 3A,
They are formed by the light beams that pass only through the virtual apertures 2A and 2B of the imaging lens 2, which are generated from the conjugate relationship with each pupil plane of the lens 3B. Therefore, now,
When the imaging lens 2 is in focus on the object 1, that is, the image Ii formed by the lens 2
are focused on the four field lens surfaces, images Ia and Ib formed by the relay lenses 3A and 3B are focused approximately at the center of each detection surface of the photoelectric detectors 5A and 5B, respectively. Assuming that the position is adjusted in advance as shown in FIG. The image Ia is shifted from the center on the photoelectric detector 5A in the direction of arrow A, and the line Ib due to the relay lens 3B is shifted on the photoelectric detector 5B from the center in the direction of arrow C. On the other hand, when the lens 2 is rear-focused (that is, the image Ii produced by the lens 2 is located behind the planned focal plane F), the image Ia produced by the relay lens 3A is at its center on the photoelectric detector 5A. Since the image Ib produced by the relay lens 3B is shifted from the center of the photoelectric detector 5B in the direction of the arrow B, and in the direction of the arrow D from the center of the photoelectric detector 5B, the photoelectric detectors 5A and 5B have a so-called position・By using a device such as a sensor whose electrical output changes depending on the position of the image on the detection surface and comparing the outputs, it is possible to determine the dependence on the relay lenses 3A and 3B. The relative relationship between the imaging positions of the two images Ia and Ib that are combined together can be detected, and therefore the focusing state of the imaging lens 2 with respect to the object 1 can be detected.

As already mentioned, in the configuration of the conventionally proposed apparatus, the third imaging optical system, that is, the field lens 4 in the configuration shown in the first diagram is not provided, and only two images are formed. a second imaging optical system for
Relay lenses 3A and 3B are the main imaging optical system,
That is, each relay lens 3A, 3 is placed behind the expected focal plane F of the imaging lens 2 so as to re-form the image formed by the imaging lens 2.
It becomes difficult to always ensure the sameness of the two images due to B, and the relay lenses 3A and 3B due to changes in the angle of view of the imaging lens 2.
There were also problems such as a large influence on the image due to the image, vignetting of the luminous flux, and a decrease in the amount of light, which resulted in the deterioration of the accuracy of focus detection.In contrast, the improvement according to the present invention In any case, the above 3rd
An imaging optical system, that is, a field lens 4 is provided so as to substantially coincide with the expected focal plane F of the imaging lens 2, so that the pupil plane of the imaging lens 2 and the relay lenses 3A, 3B are By placing the pupil planes in a nearly conjugate relationship, each relay lens 3
The two images Ia and Ib due to A and 3B are virtual apertures 2A and 2B of the imaging lens 2, respectively, resulting from the conjugate relationship between the pupil plane of the imaging lens 2 and the pupil planes of the relay lenses 3A and 3B. Since the image is formed by the light beam that passes only through the image forming lens 2, the identity of the two images can always be well maintained. Lens 3A, 3B
In addition, it is possible to completely eliminate the influence on the image caused by rays, and it is also possible to solve problems such as vignetting of the light beam or a decrease in the amount of light, and it is possible to significantly improve the accuracy of focus detection.

Now, in such a focus detection method, the relay lens 3 on the two photoelectric detectors 5A and 5B is
Since it detects the relative relationship between the imaging positions of the two images Ia and Ib based on A and 3B, the illuminance pattern of the images on the photoelectric detectors 5A and 5B formed for one object pattern is They need to be the same when the image lens 2 is focused on the object 1. To do this, the illuminance of the image Ia is determined by the luminous flux that is emitted from one point on the object within the detection field, passes through the relay lens 3A, and reaches the photoelectric detector 5A;
It is necessary to satisfy the condition that the illuminance of the image Ib due to the light flux passing through the relay lens 3B and reaching the photoelectric detector 5B is the same. In this regard, in the arrangement of the optical system shown in FIG.
If the distances ha and hb (generally ha=hb) of the optical axes 0' and 0'' of the lenses A and 3B from the optical axis 0 of the imaging lens 2 are sufficiently small, the same illuminance condition is satisfied, but hi is ha,
When it becomes larger than hb, each optical axis 0' of the relay lenses 3A, 3B of the light flux incident on the relay lenses 3A, 3B from one point on the primary image plane (F),
The difference in the incident angle with respect to 0'' becomes large, and the above-mentioned condition of the same illuminance is no longer satisfied.

The second example of improvement that attempts to solve this inconvenience is
This is an example shown in the figure. FIG. 2 shows the arrangement after the primary imaging plane (F) in the optical arrangement, and the arrangement before the primary imaging plane (F) is the same as the configuration shown in the first diagram. As shown in the figure, a fourth imaging optical system 6 (hereinafter referred to as a positive lens) is located between the field lens 4 and the relay lenses 3A and 3B, and its focal point is on the planned focal plane. It is arranged so as to almost coincide with the intersection of F (primary imaging plane) and the optical axis 0 of the imaging lens 2. In this case as well, the pupil plane of the imaging lens 2 and the relay lenses 3A, 3B
are in a conjugate relationship with each pupil plane by the field lens 4 and the positive lens 6, respectively, and the expected focal plane F and each detection plane of the photoelectric detectors 5A, 5B (this is the relay lens 3A, 3B) 2) are placed in a conjugate relationship depending on the positive lens 6 and the relay lenses 3A and 3B, respectively.

Now, in the arrangement of such an optical system, since the focal point of the positive lens 6 coincides with the planned image forming plane F, the light beam that is emitted from the planned focal plane F and passes through the positive lens 6 is parallel. Now, if we consider an arbitrary point FQ within the detection field on the planned focal plane F, a light beam emanating from the point FQ is transmitted through the positive lens 6.
The angle ω of the light beam that enters the relay lenses 3A and 3B after passing through the optical axis 0' and 0'' of the lens 2, and therefore the angle ω that it makes with respect to the optical axis 0 of the lens 2
₁ and _ω2 are equal to each other, and the light beams between the positive lens 6 and the relay lenses 3A, 3B are parallel, so that on the pupil plane of the positive lens 6 set by the relay lenses 3A, 3B. Virtual aperture 6A, 6 at
The areas of B are also equal, so the image forming points 7A, 7B on the image forming plane 7 of each relay lens 3A, 3B
This will improve the uniformity of illuminance. Further, regarding the distance d ₁ from the planned focal plane F to the front principal plane of the positive lens 6 and the distance d ₂ from the rear principal plane of the positive lens 6 to the relay lenses 3A, 3B, d ₁
= d ₂ , the angles θ 1 and θ 2 of the principal rays of the light flux directed from point FQ toward the virtual apertures 6A and 6B of the positive lens 6 with respect to the optical axis ₀ of the imaging lens ₂ are equal. Therefore, the solid angles of the two light beams directed from the point FQ toward the virtual apertures 6A and 6B become equal, and the uniformity of illuminance between the imaging points 7A and 7B on the imaging plane 7 is further improved.

The improved example shown in FIG. 2 has the above-mentioned advantages over the first example; in addition, the second example has the following advantages:
By arranging the positive lens 6 in front of the relay lenses 3A and 3B, when the rear lens 2 is in a focused state, the lens 2 formed by the relay lenses 3A and 3B
The advantage of being able to eliminate the inconvenience of a significant increase in the distance between the image points, and the relay lens 3
Even when the photoelectric detectors 5A and 5B are arranged on the imaging plane 7 of the lenses A and 3B, the centers of the detection planes should be aligned with the respective optical axes 0' and 0'' of the relay lenses 3A and 3B. (In other words, in the arrangement shown in this second example, when the lens 2 is in focus, the relay
(The centers of the images formed by the lenses 3A and 3B coincide with the optical axes 0' and 0'', respectively), which has the additional advantage that positioning and adjustment when arranging each element becomes extremely easy. It is something that can be obtained in a realistic manner.

An example of a focus detection electric circuit system applicable to the focus detection apparatus of the present invention described above will now be described with reference to FIG.

The figure shows an example in which photodiode arrays each having the same number of photodiodes are used as the photodetectors 5A and 5B. In the figure, PDA ₁ and PDA ₂ each have a predetermined number of photodiodes. Here, for example, six photo diodes PD ₁ ~
A photo diode array having an arrangement of PD ₆ , PD _{1 ′} to _{PD 6} ′, in which each photo diode PD ₁ to _{PD 6} , PD ₁ ′ to _{PD 6} ′ is connected to the relay lens 3A. , 3B, so that the centers of their light-receiving surfaces are aligned with the optical axes O', 3B of each relay lens 3A, 3B.
DA ₁ to _{DA 6} correspond to each other in position in the photo diode arrays PDA ₁ and PDA ₂ . Photos of each pair in the relationship
Diode PD ₁ ~ _{PD 1} ′, PD ₂ ~ _{PD 2} ′, ..., PD ₆
The first three photodiodes of _{the photodiode array PDA 1 are}
Each output of PD ₁ to _{PD 3} is connected to a differential amplifier DA ₁ to _{DA 3} , respectively.
and each output of the final three photo diodes PD ₄ to PD ₆ is connected to a differential amplifier.
The photo diode array is applied to each inverting input of DA ₄ to _{DA 6} .
The first three photodiodes of PDA ₂ PD ₁ ′~
Each output of PD ₃ ' is connected to each inverting input of a differential amplifier DA ₁ to _{DA 3} , respectively, and to three photo diodes at the end.
Each output of PD ₄ ′ to PD ₆ ′ is connected to a differential amplifier DA ₄ to _{DA 6,} respectively.
is applied to each non-inverting input.
Although not shown here, in general,
The output of each photodiode PD ₁ to _{PD 6} , PD ₁ ′ to _{PD 6} ′ is amplified by an amplifier, and then sent to each differential amplifier.
It is intended to be added to DA ₁ to _{DA 6} , respectively.
Incidentally, in this case, if this amplifier is a logarithmic compression amplifier, _{each pair of photo diodes PD 1 -PD 1 ′} , PD ₂ -PD ₂ ′,
..., the ratio between each output of PD ₆ to _{PD 6} ′ is determined, but this suppresses the influence of factors on changes in object brightness and influences the accuracy of focus detection due to changes in object brightness. This will be effective in preventing this from happening.
AC ₁ and AC ₂ are differential amplifiers DA ₁ to _{DA 3} and
Addition circuit for calculating the sum of the outputs of DA ₄ to _{DA 6} ,
CP ₁ and CP ₂ are for comparing the outputs of the adder circuits AC ₁ and AC _2, respectively, with respect to a predetermined reference level Vref. defined by resistors R ₁ and R ₂ (R ₁ ≫ _{R 2} ). Comparator, NOG is comparator CP ₁ ,
A NOR circuit that outputs the logical sum of the outputs of CP ₂ in inverted logic.
The gates are configured to receive the outputs of the comparators CP ₁ and CP ₂ via protective resistors R ₃ and R ₄ , respectively.

In the configuration of such a circuit system, for example, if it is assumed that the imaging lens 2 is focused on the object 1 in the arrangement of the optical system shown in FIGS. As can be understood from the arrangement of the optical system in Figures 1 and 2, at this time, the images formed by the relay lenses 3A and 3B are reflected on the light receiving surfaces of the photodiode arrays PDA ₁ and PDA ₂ . For example, if the object 1 at this time is a simple object such as a point of light, the illuminance pattern shown above will be as shown by the solid line S in FIG.・It will now coincide with the center of each light-receiving surface of array PDA ₁ and PDA ₂ , so in this case, the photo
In the diode arrays PDA ₁ and PDA ₂ , each pair of photo diodes PD ₁ ~
Since the outputs of PD ₁ ′, PD ₂ ~ _{PD 2} ′..., PD ₆ ~ _{PD 6} ′ are almost the same, the differential amplifier DA ₁ ~
The output of DA ₆ is almost zero. Therefore, since the outputs of the adder circuits AC ₁ and AC ₂ are also almost zero, the outputs of the comparators CP ₁ and CP ₂ are both low, and in the end, in this case, the NOR gate NOG
Only the output of is high.

On the other hand, when the imaging lens 2 is front focused with respect to the object 1, the relay lens 3
The illuminance pattern of the images formed by A and 3B on the light receiving surfaces of the photo diode arrays PDA ₁ and PDA ₂ is as shown by the broken line T in FIG. is a photo diode array
The light receiving surface of PDA ₁ is shifted in the direction of arrow A, and the light receiving surface of photo diode array PDA ₂ is shifted in the direction of arrow C. Therefore, in this case, the differential amplifier DA _The outputs of the differential amplifiers DA ₄ to _{DA 6 are} positive values, so the outputs of the comparator CP ₁ are low and the outputs of the comparator CP ₂ are low. This causes the output of the NOR gate NOG to go low.

Conversely, when the imaging optical system L ₁ is rear-focused with respect to the object, the image formed by the imaging lenses L ₂ and L ₃ is reflected by the photo diode array PDA _1. , the illuminance pattern on each light-receiving surface of PDA ₂ is as shown by the two-dot chain line U in FIG.
The center of the image is a photo diode array PDA ₁
The light receiving surface of the photo diode array PDA 2 is shifted in the direction of arrow B, and the light receiving surface of the photo diode array PDA ₂ is shifted in the direction of arrow D. Therefore, in this case, the differential amplifiers DA ₁ to The output of DA ₃ will be a certain positive value, while the output of the differential amplifiers DA ₄ to _{DA 6} will be a certain negative value, so the output of comparator CP ₁ will be high and the output of comparator CP ₂ will be low. ,or,
As a result, the output of the NOR gate NOG becomes low.

Note that _{the comparators CP 1 ,} CP ₂ and Noah's
The relationship between each output of the gate NOG is as shown in FIG.

Therefore, according to the configuration of the circuit system shown in FIG. 3, for example, as shown in the figure, the comparator
NPN switching transistors _{Tr 1 , Tr 2 ,}
The respective bases of Tr ₃ are connected through protective resistors R ₃ , R ₄ , R ₅ , and these transistors Tr ₁ , Tr ₂ , Tr ₃
By connecting the light emitting diodes LD ₁ , LD ₂ , LD ₃ as display elements together with the protective resistor R ₆ to the respective collector sides of the , the pin state after the light emitting diode LD _{1 changes depending on the lighting of the light emitting diode LD 1} . Also, light emitting diode
The front focus state depends on the lighting of LD ₂ , and the focusing state depends on the lighting of light emitting diode LD ₃ .
This means that they will be displayed accordingly.

Furthermore, in the configuration of the detection circuit system shown in FIG. 3, for example, the outputs of the comparators CP ₁ and CP ₂ may be used to control the motor for driving the imaging optical system L ₁ . This also enables automatic focus adjustment of the imaging optical system _L1 , which will be explained with reference to FIG.

In the figure, Tr ₄ and Tr ₅ as well as Tr ₆ and Tr ₇ are npn switching transistors that are connected complementary to each other, and the collectors of transistors Tr ₄ and Tr ₆ are connected to the positive side of the power supply through a protective resistor R ₉ . Furthermore, the emitter sides of transistors Tr ₅ and Tr ₇ are connected to ground, respectively, and the output of the comparator CP ₁ is connected to the base of each transistor Tr ₄ and Tr ₅ through a protective resistor R ₇ , and the transistor Tr ₆ , the output of the comparator CP ₂ is applied to each base of Tr ₇ through a protective resistor R ₈ ,
The lens drive motor Mo is a transistor.
It is inserted and connected to the complementary connection lines of Tr ₄ , Tr ₅ and Tr ₆ , Tr ₇ .

In such a connection configuration, when the imaging lens 2 is in the rear pin state, only the output of the comparator CP ₁ becomes high, so that the transistors Tr ₆ and Tr ₇
remains off, transistors Tr ₄ and Tr ₅ are turned on, and the motor Mo is energized in the direction of arrow X in the figure, causing it to rotate forward, for example _. Since only the output of transistors Tr ₄ and Tr ₅ remain off, transistors Tr ₆ and Tr ₇ turn on, and the motor starts.
For example, Mo is reversed by being energized in the direction of the arrow Y in the figure, and in the focused state, the outputs of the comparators CP ₁ and CP ₂ both become low, so that the transistors Tr ₄ to _{Tr 7} are activated. Both are turned off, and the motor Mo comes to stop due to the current being cut off. Therefore, due to the forward rotation of the motor Mo, the imaging lens 2 moves forward along its optical axis _O1 . By connecting the output shaft of the motor Mo to the imaging lens 2 through an appropriate mechanism, the imaging lens 2 is automatically moved so that it is extended and retracted backwards by reversing. This allows focus adjustment to be achieved.

In addition, in the detection circuit system shown in Figure 3, the resistor
As can be understood from the above explanation, the reference level Vref set for the comparators CP ₁ and CP ₂ by R ₁ and R ₂ defines the range that is considered to be in focus. , and this means that as the value approaches zero, the range that is considered to be in focus becomes narrower, and the accuracy of the focused state of the imaging lens 2 improves. In general, for example, when used in a camera or the like, it is a good idea to take into consideration the depth of focus of the photographic lens and set the value appropriately within a range that does not cause any practical problems.

Finally, some examples will be described in which the focus detection device of the present invention is applied to a single-lens reflex camera.

First, FIG. 6 shows an example of the case where the configuration of the focus detection device shown in FIG. Movable reflective mirror for
Reference numeral 14 denotes a focus plate disposed at a position conjugate with the film 12 with respect to the mirror 13, and here, as shown in FIG. Therefore, this transparent portion 14 is formed as a transparent portion.
It is formed as a ground glass surface except for a.
15 is a condenser lens arranged close to the focus plate 14, 16 is a penta prism, and 17 is an eyepiece lens.

Regarding the arrangement of the optical system of such a camera, the eighth
As shown in the figure, a relay lens 18 for forming two images.
A and 18B (this is the relay lens 3 shown in the first diagram)
A and 3B (corresponding to the second imaging optical system) are arranged so as to face the light exit surface of the penta prism 16 and sandwich the eyepiece lens 17 (preferably with respect to the optical axis of the eyepiece lens 17). symmetrically) and each relay lens 18
Reflection prism 19 placed behind A and 18B
Photoelectric detectors 20A and 20B are arranged to coincide with the imaging planes of the relay lenses 18A and 18B, respectively, which are set by the relay lenses 18A and 19B. In this embodiment, the first illustrated field lens 4 - the third imaging optical system - is also used as a condenser lens 15, and therefore, the condenser lens 15 is located on the pupil plane of the photographing lens 11. and relay lens 18A, 1
A lens having a focal length sufficient to establish a conjugate relationship with each pupil plane of 8B is selected. Similarly, the relay lenses 18A and 18B are selected to have focal lengths sufficient to establish a conjugate relationship between the surface of the focusing plate 14 and the detection surfaces of the photoelectric detectors 20A and 20B, respectively.

In this way, the optical arrangement of the focus detection optical system explained with reference to FIG. 1 is satisfied, and the focus of the photographing lens can be detected with high precision with the above-mentioned advantages. .

Next, FIG. 9 shows a first example in which the configuration of the focus detection device shown in FIG. 2 is applied, and in the figure, elements denoted by the same symbols as in FIG. has exactly the same configuration and function as described above. 14' is a focusing plate disposed at a position conjugate with the film 12, as shown in the figure.
A convex lens portion 14'a is formed at the center thereof. Note that 14'b is a well-known split prism. A condenser lens 15' is disposed close to the focusing plate 14', and has a 45-degree oblique semi-transparent mirror portion 15'a at its center. 21
is opposite to the exit end surface of the reflected light beam that is reflected laterally (i.e., to the right in the figure) by the semi-transparent mirror portion 15'a of the condenser lens 15', and directs the output light beam upward. The reflecting prisms 22 and 23 provided for reflection are two lenses constituting a positive lens system, which are provided close to the light output end face of the prism 21, and their optical axis is aligned with the mirror 13.
and a photographing lens 2 based on the semi-transparent mirror section 15'a.
It is set in advance so that it coincides with the extended optical axis of , and its combined focus coincides with the surface of the focus plate 14'. 25A and 25B (shown in FIG. 10) are two relay lenses for forming two images arranged so as to sandwich the optical axis of the lenses 22 and 23 (preferably symmetrically with respect to the optical axis). corresponds to the second illustrated relay lenses 3A and 3B - the second imaging optical system), and 24 corresponds to the respective relay lenses 25A and 2
A mask plate for limiting the incident light flux to 5B has two apertures 24a, 24b (shown in FIG. 10), and each aperture 24a, 24b faces each relay lens 25A, 25B. It is placed in front of the etc. 26 is the relay lens 2
Reflection mirrors placed behind 5A and 25B,
A photoelectric detection means 27 is arranged to coincide with the imaging plane of the relay lenses 25A, 25B set by the mirror 26. The photoelectric detection means 27 includes, for example, two photoelectric detectors 2 as shown in FIG.
7A and 27B, and each photoelectric detector 27A, 27B has a relay lens 25, respectively.
A, 25B (preferably, the center of each detection surface is aligned with each relay lens 25A, 25B)
5B). Incidentally, 28 is a light shielding plate provided for the purpose of preventing the two images produced by the relay lenses 25A and 25B on the photoelectric detectors 27A and 27B from overlapping, and is treated with anti-reflection treatment using, for example, electrostatic flocking. ing.

Here, the convex lens portion 14'a formed on the focus plate 14' is the second field lens 4 (the third field lens shown in the figure).
(imaging optical system), and the positive lens system consisting of lenses 22 and 23 is a positive lens 6 (fourth imaging optical system).
The pupil plane of the photographing lens 11 and the relay lenses 25A, 25 correspond to the positive lens system consisting of the convex lens portion 14' and the lenses 22, 23, respectively.
B is placed in a conjugate relationship with each pupil plane, and the focusing plate 14' plane and the photoelectric detectors 27A, 27B are detected by the positive lens system consisting of the lenses 22, 23 and the relay lenses 25A, 25B. The specifications and optical arrangement of each optical element are determined so that the optical element is in a conjugate relationship with the surface.

In this way, the optical arrangement of the focus detection optical system explained with reference to FIG. 2 is satisfied, and the focus of the photographic lens 11 can be detected with high precision with the above-mentioned advantages. be.

Finally, FIG. 12 shows a second example in which the configuration of the focus detection device shown in FIG. Instead of being built into the mirror box, it is built into the bottom of the mirror box. In this figure, elements indicated by the same reference numerals as in FIGS. 6, 8, and 9 have the same structure and function as described above. Reference numeral 13' denotes a movable reflection mirror for the viewfinder, and a fully transparent or semi-transparent aperture 13' is provided at a symmetrical position with respect to the optical axis O of the photographing lens 11.
a, 13'b, and the light flux passing through these apertures 13'a, 13'b is reflected by the mirror 1.
The light is reflected downward, ie, toward the bottom of the camera, by a submirror 29 mounted behind the mirror 3'. 30 is a field lens arranged at a position conjugate with the film 2 with respect to the sub mirror 29 (this corresponds to the second illustrated field lens 4 - the third imaging optical system); 31 is the field lens 30; A positive lens is disposed behind the field lens 30 so that its focal point coincides with the center of the field lens 30, that is, the center of the film conjugate position. 32A and 32B are for receiving the two beams of light from the apertures 13'a and 13'b reflected by the sub-mirror 29 through lenses 30 and 31, respectively. Two relay lenses (this is the second illustrated relay lens 3) are juxtaposed behind the positive lens 31 so that their optical axes are symmetrical with respect to the optical axes of the lenses 30 and 31.
A and 3B - corresponding to the second imaging optical system),
33A and 33B are respective relay lenses 32A and 33B in order to detect the relative relationship between the imaging positions of the images formed by the relay lenses 32A and 32B, respectively.
32B is a photoelectric detector arranged near the imaging plane so that the center of each detection plane coincides with the optical axis of each relay lens 32A, 32B, as shown in FIG. 3. A photodiode array configuration is utilized. 34 is a circuit unit that detects the focus adjustment state of the photographing lens 11 based on the outputs of the photo diode arrays 33A and 33B, and here, it is a circuit unit that detects the focusing state of the photographing lens 11 based on the outputs of the photo diode arrays 33A and 33B, and here it is based on a combination of the third detection circuit shown in the figure and the fifth motor control circuit shown in the figure. It has a structure. Reference numeral 39 denotes a light emitting element for displaying focus, which corresponds to the light emitting diode LD ₃ for displaying focus in FIG. It is being
Reference numeral 35 denotes a photographing lens driving motor, which corresponds to motor Mo in FIG. are doing.

Here, the pupil plane of the photographing lens 11 and the pupil planes of the relay lenses 32A and 32B are placed in a conjugate relationship with each other by the field lens 30 and the positive lens 31, and the positive lens 31 and the relay lenses
Field lens 3 depending on lenses 32A and 32B
The specifications and optical arrangement of each element are selected in advance so that the 0 plane, that is, the film conjugate plane, and the detection planes of the photo diode arrays 32A and 33B are in a conjugate relationship with each other. .

In the configuration of such a camera, as described above, automatic focusing of the photographing lens 11 is achieved through the control of the motor 35 by the circuit unit 34, and the focusing state is determined by the lighting of the display element 39. For example, it will be displayed in the viewfinder, but in this case, the optical arrangement of the focus detection optical system explained in Fig. 2 is satisfied, so in addition to the above-mentioned advantages, 11 focus detection can be performed with high precision.

Incidentally, in the configuration of the focus detection system shown in FIG. 12, the light flux incident on the relay lenses 32A, 32B is caused by the apertures 13'a, 13'b of the viewfinder mirror 13', In particular, it is controlled so that the luminous flux comes from the peripheral area, but as is well known, the peripheral luminous flux of the lens is
The angle it makes with respect to the optical axis is large, and therefore, with this configuration, the relay and the Since the ratio of relative change in the imaging position of each image formed by the lenses 32A and 32B becomes large, this is even more effective in improving the accuracy of focus detection.

In the example of the single-lens reflex camera described above, the photoelectric detectors 20A and 20B in the sixth to eighth illustrated examples and the photoelectric detectors 27A and 27B in the ninth to 11th illustrated examples are A photo diode array as shown in Figure 3 also
The configurations of PDA ₁ and PDA ₂ can be used, and the circuit configuration shown in FIG. 3 can also be used as is for the electric circuit for focus detection.

Further, the configurations of the ninth to eleventh illustrated examples are, for example, the ninth to eleventh illustrated examples.
The two lenses 22 and 23 constituting the positive lens system shown in Fig. 10 are omitted and the photographing lens 1 is
The pupil plane of the lens 1 and the pupil planes of the relay lenses 25A and 25B are placed in a conjugate relationship with each other by the convex lens portion 14'a of the focusing plate 14', and the pupil plane of the focusing plate 14' (film conjugate surface) Photoelectric detector 27A, 27B
On the other hand, in the configuration of the twelfth illustrated example, for example, the positive lens 31 is omitted and the pupil of the photographing lens 11 is surface and relay
The pupil planes of the lenses 32A and 32B are placed in a conjugate relationship with each other by the field lens 30, and
The specifications of each optical element and the optical By selecting the arrangement relationship anew, each single-lens reflex camera follows the configuration shown in the first diagram.
This allows it to be used directly in the configuration of a camera.

As described in detail above, according to the present invention, it is applied to a single-lens reflex camera, and the relative relationship between two images formed based on light passing through the main imaging optical system including a photographic lens is achieved. As a TTL focus detection device that detects the focus adjustment state of the main imaging optical system with respect to the object by detecting changes in the imaging position, it is possible to improve this by improving the identity of the two images. In addition to ensuring that
It is possible to almost completely eliminate the influence of factors on changes in the angle of view of the main imaging optical system with respect to the image, and it is also possible to effectively avoid problems such as vignetting of the luminous flux or reduction in the amount of light. This type of device is extremely useful because it has the remarkable effect of dramatically improving accuracy.

Moreover, according to the improved example shown in FIG. 2, in addition to the above-mentioned advantages, it is possible to sufficiently guarantee the sameness of the illuminance of the two images, and each image point of the two images can be It is possible to eliminate the inconvenience of a significant increase in the separation distance between the focus detection system, and to obtain additional advantages such as extremely easy optical positioning and adjustment of each optical element constituting the focus detection system. and
Therefore, this type of focus detection device is increasingly useful.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing, in particular, the principle arrangement of the optical system of an embodiment of the focus detection device according to the present invention, and FIG. FIG. 3 is a schematic diagram showing the principle arrangement of the optical system in parts different from the configuration; FIG. 3 is a circuit diagram showing an example of a focus detection electric circuit system applicable to the focus detection device of the present invention; FIG. 4 5 is a diagram showing the output relationship of the circuit system shown in the third diagram with respect to the focus adjustment state of the main imaging optical system, and FIG. FIG. 6 is a partial circuit diagram showing an example of the motor control circuit used, and FIG. 6 is a plan view of the focusing plate in the camera shown in FIG. 6, FIG. 8 is a perspective view of the focusing plate in FIG. 6, and FIG. FIG. 10 is a main part configuration diagram showing a schematic configuration of an example of
11 is a schematic diagram showing details of the photoelectric detection means in FIG. 9, and FIG. 12 is a schematic diagram showing the improved example shown in FIG. 2 in a single-lens reflex camera. FIG. 7 is a perspective view of a main part configuration showing a schematic configuration of a second example. 1... Object, 2; 11... Main imaging optical system (imaging lens or photographing lens), F; 12... Planned focal plane (film surface), 3 (3A, 3B); 18
A, 18B; 25A, 25B; 32A, 32B...
...Second imaging optical system (relay lens for forming two images), 4; 15; 14'a; 30...Third imaging optical system (field lens - condenser lens or convex lens section), 6 ;22,23;31...Fourth imaging optical system (positive lens or positive lens system), 5
A, 5B; PDA ₁ , PDA ₂ ; 20A, 20B; 27
(27A, 27B); 33A, 33B...Photoelectric detection means (photo diode array), 13'...
...Aperture means (reflection mirror for finder), 13'
a, 13'b...opening.

Claims (1)

[Claims] 1. An image of an object formed by the main imaging optical system behind the intended focal plane of the main imaging optical system to be focused on the object. A plurality of second imaging optical systems that form two images are juxtaposed in such a manner that their respective imaging positions change relatively in accordance with changes in position on the optical axis, and the second imaging optical systems are arranged in parallel. A focus detection device configured to detect a focus adjustment state of the main imaging optical system with respect to the object by detecting a relative change in the imaging position of the two images focused by the optical system, A third imaging optical system is provided at least near the planned focal plane of the main imaging optical system, and a fourth imaging optical system is provided between the third imaging optical system and the second imaging optical system. An imaging optical system is disposed coaxially with its focal point substantially coinciding with the planned focal plane of the main imaging optical system,
At this time, the third and fourth imaging optical systems are arranged so that the pupil plane of the second imaging optical system is placed in a substantially conjugate relationship with the pupil plane of the main imaging optical system. Features a focus detection device. 2. The optical path length from the planned focal plane of the main imaging optical system to the front main surface of the fourth imaging optical system, and from the rear main surface of the fourth imaging optical system to the second imaging optical system. The focus detection device according to claim 1, wherein the optical path length is approximately equal to the optical path length to the pupil plane of the system.