JPS636532A - Automatic focusing camera capable of proximity photographing - Google Patents

Abstract

PURPOSE:To obtain a correct focus by allowing a short distance correcting optical element to interlock with a driving ring, and allowing it to advance to the front of a photodetecting part, at the time of proximity photographing, in a camera for moving a photographic optical system by the driving ring between regular photographing and promixity photographing. CONSTITUTION:A light beam from a light source 3a is emitted to an object to be photographed, a reflected light is received by a photodetecting lens 4b, a light source image shift quantity to a distance to the object to be photographed is derived by a position detecting element 4a, and focusing is executed by moving a photographic optical system to a focal position. In such a case, at the time of proximity photographing, a short distance correcting optical element 4e is positioned in front of the photodetecting lens 4b by allowing it to interlock with a driving ring of the photographic optical system. Its optical element 4e is constituted of a prism 4c and a mask 4d. By its optical element 4e, a base line length of a distance measuring device 4 is extended optically to a distance L + l, a light source image shift quantity t2 against a distance Umf2 of the object to be photographed is set to the same degree as a shift quantity of regular photographing, and the photographic optical system is focused to the focal position. Accordingly, at the time of proximity photographing, the short distance correcting optical element is positioned in front of the photodetecting lens automatically, and the distance measuring accuracy can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to autofocus cameras, and particularly to cameras capable of close-up photography.

"Prior Art" First, the relationship between the object distance and the extension amount of the two-group zoom lens will be described. FIG. 12 shows a simple configuration of a two-group zoom lens.

The equation showing the relationship between the subject distance and the amount of extension is as follows.

U = f+ (2+X/fl+fl/X)+HH 18・
・■ However, U: Subject distance fl: Focal length of the 1st group and X・(-2f+-HH-△+u-++ +l\-u
4f+)/2...■.

On the other hand, Fig. 13 shows a distance measuring optical system based on the triangulation principle (
(M) object distance U and the amount of deviation t on the position detection element 2
shows the relationship between

The bigonal distance measuring device is composed of a light projecting section 3 consisting of a light source 3a and a projecting lens 3a, and a light receiving section 4 consisting of a light receiving lens 4b and a position detecting element 4a (for example, a PSD). The distance to the subject is detected by obtaining the reflected light from the subject using the position detection element 4a. In other words, the distance MU from the film plane F to the subject
The amount of deviation t of the light source image on the position detection element 4a (the reference is the position M of the light source image when the object is infinite) is calculated using the following formula (%). However, L: Base length of the distance measuring device f: The distance of the light receiving lens Focal length d: As is well known, the distance t between the film surface and the focal plane of the light-receiving lens can be detected by the magnitude of the photocurrent of the position detection element 4a. If the lens is moved to the focal position based on formulas (1) and (2) above, focusing will be achieved automatically. Such autofocus cameras and drive mechanisms for photographic optics are known.

With this autofocus camera, close-up photography (macro photography)
When adding a function, it is necessary to shift the measurable range of the distance measuring device to the short distance side.

As is well known, the close-up shooting function moves all or part of the photographic optical system closer to the subject than during normal shooting.
A focusing operation is performed in this state. In the photographing optical system shown in FIG. 12, the first lens group of the photographing lens is extended by a fixed amount during close-up photography, in addition to the amount extended by the autofocus device during normal photography.

Figure 14 shows a conventional example in which the measurable distance M range of the distance measuring device is shifted to the short distance side. As shown in the figure, by arranging a prism P with an apex angle of 6 in front of the light receiving lens 4b, distances M&! You can shift the range to the short distance side.

When the apex angle of the prism P is 6 and the refractive index is tn, the shift amount t of the light source image on the position detection element 4a with respect to the object distance U can be determined by the following procedure.

The angle of incidence α of a ray of light onto the surface of the prism P on the subject side is determined by the following equation.

a = tan-'(L/(U+ -f -a))+6
When a ray of light enters a prism with an angle of 6 at an incident angle α, the deflection angle β is determined by the following equation.

β: α-6+5in-'[n5in(6-sin(a/
n))] Therefore, ]γ=α−6− In addition, the amount of shift t of the light source image on the position detection element 4a is t+
= f4any. Umf+ is the subject distance when a ray that partially intersects the optical axis of the projecting lens 4 intersects with the optical axis of the projecting lens 3b.If the thickness of the prism P is ignored, Umf+
=L/1an(sin-'(nsin6)-6)
+ f + d.

Here, as an example, with a photographic optical system or a 2-detail zoom lens,
Focal length of the 1st group f + = 24.68 mm 1 Principal point spacing HH 7.02 mm 5 Distance between the focal position of the 1st group and the focal position of all groups Δ 30.04 mm Distance between the film surface and the focal plane of the light receiving lens d = 6.292 mm, shift amount of the first group during close-up photography 0.5502 mm, base line length of the distance measuring device L = 30 mm, focal length of the light receiving lens f・20 m
m, the apex angle of the prism P is 6.2.826", the refractive index of the prism is n = 1.483, and the range of photographic distance is 0.9.
At 73m-ω, the number of feeding steps is 18, of which 0.97.
In the case where the camera has a feeding mechanism that divides 3m to 6m into 17 stages (this calculation was performed for the case where the shooting range of 0.973m to 6m is shifted to the shooting range of 0.580m to 1.020m using prism P). The results are shown in Table 1.

In the table, 17-18 indicates the switching point between the 17th stage and the 18th stage, and 0-1 is the same.

(Left below) Usf+”1.283m From the results in Table 1, it can be seen that with the correction using prism P, the position detection element 4
It can be seen that a deviation of 0.027 mm occurs on a. This is a shift amount equivalent to approximately one stage when converted to the number of stages of feeding. Therefore, if the photographing optical system is controlled to move forward as it is based on the output of the position detection element 4a, the photographing lens cannot be moved to the correct focusing position, resulting in an out-of-focus photograph.This is due to the fact that the prism P This is due to the fact that complete correction is impossible because it is not possible to change the rate of change of the deviation jit+ of the light source image on the position detection element 4a with respect to the subject distance U only by correction.

[Object of the Invention] An object of the present invention is to improve the distance measurement accuracy during close-up photography and realize more ideal focus correction in an autofocus camera having a distance measurement optical system using triangular distance measurement. Another object of the present invention is to provide an autofocus camera that can automatically configure a distance measuring optical system for close-up photography in conjunction with the transition from normal photography to close-up photography.

"Summary of the Invention" Basically, in the discussion of Table 1 above, the present invention provides that the amount of change in t from +7-18 to o-1 is 0.5.
334mm The amount of change in t+ is 0.4794mm, so the change in tl during close-up photography is 0.533410
．． This was done based on the idea that complete correction would be possible if the magnification was increased to 4794 times, or 1.1130 times, and for this reason, it was placed in front of the distance-measuring optical system during close-up photography.
The base line length between the light emitting part and the light receiving part of the distance measuring optical system is optically extended, and a short distance correction optical element is arranged to intersect the optical axes of the light emitting part and the light receiving part at a finite distance. It is characterized by And the present invention is rough.

In addition, a mechanical configuration is provided for moving this short-distance correction optical element to the front of the light-receiving section in conjunction with the camera's transition operation between normal shooting and near-width shooting. That is, the present invention
A driving ring of the photographing optical system which performs a transition between normal photography and close-up photography by rotational operation; A correction flag having four parts pivoted to move it forward and backward in front of the light receiving section; a spring means that normally biases this correction flag in a direction in which its short-range correction optical element retreats from the front surface of the light receiving section; and a drive ring. The drive ring and the correction flag are arranged to rotate the correction flag against the spring means in conjunction with the rotation movement of the drive ring to the appropriate close-up position, and to position the short-range correction optical element in front of the light receiving section. The invention is characterized in that it has an interlocking means provided in between.

Regarding the optical system other than the mechanical structure, the present applicant has filed a separate patent application in Japanese Patent Application No. 108279/1982 (filed on May 12, 1961).

``Embodiment of the Invention'' FIG. 9 shows the optical configuration of the distance measuring device for an autofocus camera according to the present invention during close-up photography. The basic configuration is that the correction optical element 4e is placed in front of the light receiving lens 4b of the distance measuring device during close-up photography, and is retracted from the optical axis of the light receiving lens 4b during normal bottle shadowing.

Before explaining the mechanical configuration for moving the short-distance correction optical element 4e back and forth in front of the light-receiving lens 4b, the structure of the short-distance correction optical element 4e and the reason why distance measurement accuracy in close-up photography is improved will be explained.

The prism 4C has the effect of optically extending the base line length of the distance measuring device and the effect of refracting light rays. FIG. 10 shows a detailed top view of the prism 4c, mask 4d, and light-receiving lens 4b, and FIG. 11 is a front view of FIG. 10.

The mask 4d is for blocking light other than the necessary optical path, and has an aperture 4f on the subject side and an aperture 49 on the light receiving lens 4b side.
have. The aperture 4f is opened in a slit shape at a distance ρ on the side away from the optical axis of the light emitting lens 3b with respect to the optical axis ○ of the light receiving lens 4b, and the aperture 49 is spaced apart from the optical axis Q of the light receiving lens 4b. It is opened in a slit shape to correspond to the

The prism 4c with the mask 4d is the light receiving lens 4b.
When the camera is placed in front of the camera, that is, during close-up photography, the first lens group of the photographic lens is extended by a fixed amount in addition to the amount extended by the automatic focus device during normal photography. By arranging the prism 4C in front of the light-receiving lens 4b as shown in FIGS. 1 and 2, the range of alternating layers in which distance can be measured can be shifted to the short distance M side. The prism 4c optically extends the base line length to L+ρ by translating the light beam incident thereon by l in the direction of the base line length.

If the angle of this prism 4C is 69, the refractive index is n, and the parallel movement of the light beam j1 is β as above, then the object distance U
The amount of deviation t2 of the light source image on the position detection element 4a with respect to the position detection element 4a can be determined by the following procedure.

The angle of incidence α of the light beam onto the object-side surface of the prism 4C is obtained from the following equation.

a +=tan-'((L+β)/(12-f-d))
-6.

This formula means that the base line length for triangulation snowmaking is extended from before the prism 4C is inserted to L+β after the prism 4C is inserted.

Angle 6. When a ray of light enters the prism at an angle of incidence α, the deflection angle β can be obtained from the following equation.

B +=a +-6+"5in-' [n5in(6
+-5in(a +/n))] Therefore, ]γ1=α word-
6bi β Therefore, the amount of deviation t2 of the light source image on the position detection element 4a is t2
=ftany+, Umf is the subject distance when a ray that is part of the optical axis of the light receiving lens 4b intersects with the optical axis of the projecting lens 3b, and if the thickness of the prism 4c is ignored, then Umf2 = (L + β) / 1an(sin-'(nsin
It is expressed as 5+)-6+)・f+d.

Here, a case will be described in which the present invention is applied to a photographic lens under the same conditions as in the above-mentioned example. In other words, the photographic lens is a two-group zoom lens, and the focal length of the first group is M f ++24.6.
8n+m, distance between principal points = 7.02mm, distance between the focal position of the first group and the focal position of all groups △・30.04mm, distance d between the film surface and the focal plane of the light receiving lens = 6.292m
m, shift amount of the first group during close-up shooting 0.5502 mm
, base line length L of distance measuring device = 30 mn+, focal point f of light receiving lens = 20 mm, angle of prism 4c 6, = 3
．． 39°, refractive index n・1.483, amount of parallel movement of light 1
2 = 3.39mm, shooting distance M range is 0.97
At 3m~ω, the number of stages is 18, of which 0.973.
When having a feeding mechanism divided into 17 stages of m to 6 m,
Table 2 shows the results of performing a total of X for the case where the photographing range of 0.973 m to 6 m is shifted to the fiVV range of 0.580 m to 1.020 m by the prism 4C.

(Margin below) Usf+” 1.283m From the results in Table 2, the difference in each stage of the light source image on the position detection element 4a during normal shooting and close-up shooting is ±0.000.
It can be seen that the thickness is suppressed to 1 mm or less.

Therefore, if the photographing optical system is controlled in accordance with the output of the position detection element 4a, a photograph with almost perfect focus can be obtained.The results shown in Table 1 show that the prism 4C
Optically, the baseline length for close-up photography is 1.
This shows that the length was extended by H3 times (30 mm→33.39 mm), and the amount of movement on the position detection element 4a was increased by 1.113 times.

Next, referring to FIGS. 1 to 8, in conjunction with the transition between near Wi shooting and normal shooting, the short distance correction optical element 4e
A mechanical configuration for advancing and retracting the light receiving lens 4b in front of the light receiving lens 4b will be explained.

In this embodiment, the present invention is applied to a lens-shutter camera having a zoom lens system, including a zoom lens barrel block 1, a finder, and a strobe block 2).
It is equipped with a light projecting section 3, a light receiving section 4, and a zoom motor 5 for zooming based on the above-mentioned triangulation principle. These elements are fixed on a base plate 6 which serves as a fixed part of the camera body. If the light projector 3 and the light receiver 4 are arranged on both sides of the zoom motor 5, the base line length L18 can be reduced with increased space efficiency.
:Can be made large.

These elements are fixed on a base plate 6 (see FIGS. 2 to 5) which serves as a fixed part of the camera body. That is, the base plate 6 includes a lens barrel support plate part 6a that is perpendicular to the optical axis, a horizontal support plate part 6b that is bent at a right angle to the upper end r8 of this lens barrel support plate part 6a, and a horizontal support plate part 6b that is bent at a right angle to the upper end r8 of this lens barrel support plate part 6a. The lens barrel block 1 is supported by the lens barrel support plate 6a. Further, a zoom motor 5 located at the upper center of the lens barrel block 1 is fixed to the motor support plate portion 6C.
A light projecting section 3 and a light receiving section 4 fixed to the horizontal support plate section 6b are located on both sides of the horizontal supporting plate section 6b.

The finder block 2 is fixed to the front right side of the horizontal support plate portion 6b. 6e is a gear train support plate fixed to the motor support plate portion 6C via a spacer 6f.

The structure of the lens barrel block 1 driven by the zoom motor 5 will be explained with reference to FIGS.
1 is fixed. After this, four guide rods 12 are fixed to the fixing plate 11 parallel to the optical axis and located around it, and the front fixing plate 1 is attached to the tip of the guide rod 12.
One or more elements to which 3 is fixed are the main fixing elements of the lens barrel block 1.

A cam ring (driving ring) 14 is rotatably supported between the rear fixed plate 1] and the front fixed plate 130, and a cam ring (drive ring) 14 is rotatably supported on the outer periphery of the cam ring 14. Alternatively, the gears 15 that mesh through the gear train are fixed with fixing screws 5a (FIG. 6). This gear 15 is a sector gear that covers the rotation range of the cam ring 14. The cam ring 14 includes one for the front group,
A zooming cam groove 20.2 for the rear group is cut.

FIG. 7 is a developed view of the zooming cam grooves 2o and 21, and the zooming cam groove 21 for the rear group includes a wide-angle end fixed section 21a, a variable power section 21b, and a telephoto end fixed section 21c! have. On the other hand, the zooming cam groove 20 for the front group includes the opening/closing section 20a of the barrier block 30, the lens storage section 20b, the wide-angle end fixed section 20c, the variable power section 20d, the telephoto end fixed section 20e, the macro feed section 2Of, and the lens storage section 20b. It has a mouth end fixed section 209. The rotation angle of each of these sections is the total angle of the opening/closing section 20a of the zooming cam groove 2o, the lens storage section 20b, and the wide-angle end fixing section 20c. is the same as the angle 61 of the wide-angle end fixed section 21a of the zooming cam groove 21, the angle 62 of the variable magnification section 20d and the variable magnification section m21b is the same, and the angle 62 of the variable magnification section 20d and variable magnification section m21b is the same, and the angle 62 of the variable magnification section 20d and variable magnification section m21b is the same, and The total angle 63 of the fixed section 209 is the same as the angle 63 of the telephoto end fixed section 21c. Note that the specific zooming range of this example is 35 mm.
~70mm, it is possible to roughly extend macro from the telephoto end (70mm).

These zooming cam grooves 20 and 21
The front group frame 16 is movably fitted to the guide rod 12.
The roller 17 of the rear group frame 18 and the roller 19 of the rear group frame 18 are fitted.

A decorative frame 22 is fixed to the front group frame 16 via fixing screws 22a, and a shutter block 23 is roughly fixed to the front group frame 16. The front group lens L1 and the held front group lens frame 24 are screwed together with this shutter pro-v 23 by a helicoid 25, and also have an arm 24a that engages with a lens extension lever 23a of the shutter block 23. are doing. Therefore, when the lens advancing lever 23a rotates in the circumferential direction and the front group lens frame 24 rotates accordingly, the front group lens frame 24 rotates.
4 moves in the optical axis direction according to the helicoid F:25. The rear group lens L2 is directly fixed to the rear group frame 18.

As is clear from the above configuration, the lens barrel block 1 rotates the cam ring 14 by the zoom motor 5,
When the roller 17 of the front group frame 16 is engaged with the macro mouth end fixing section 209 from the macro feed section Fffi2Of of the zooming cam groove 20, a close-up shooting state is established in which the front group lens L1 is further moved out than during normal shooting.

As shown in FIGS. 1, 2, and 4, the short distance correction optical element 4e, which is a feature of the present invention, has its base end connected to the base plate by a shaft 41 located below the light receiving section 4. The correction flag 42 is fixed to the free end of the correction flag 42 which is pivotally connected to the correction flag 6. This correction flag 42 maintains its linearity when no external force is applied to it, but when an external force is applied to it, it has the visibility of being elastically deformed. An interlocking protrusion 43 is integrally provided at the other end of the correction flag 42. Further, the short distance correction optical element 4e is rotatably biased by a tension spring 46 in a direction in which the short distance correction optical element 4e retreats from the front of the light receiving section 4 during lightning. The cam ring 14 is provided with an advancing protrusion 44 that engages with the movable protrusion 43 to advance the short distance correction optical element 4e to the front of the light receiving section 4 when the cam ring 14 is rotated to the close-up photographing position. The position and shape of the protrusion protrusion 44 are determined so as to rotate the short distance correction optical element 4e more than the front surface of the light receiving section 4, but the rotation by the protrusion protrusion 44 of the short distance correction optical element 4e is The side surface of the gear support plate 6e, which is integral with the base plate 6, regulates, and the overcharge caused by the advancing protrusion 44 is absorbed by the visibility of the correction flag 42.

According to the above structure, when the cam ring 14 rotates for the close-up shooting function, the short-distance correction optical element 4e can be automatically positioned in front of the light receiving section 4.

Note that a drive signal to the shutter block 23 from the distance measuring device that illuminates the light projecting section 3 and the light receiving section 4 is sent via a flexible printed circuit board (FPC board) not shown. This flexible printed circuit board is bent and arranged inside the cam ring 14 so that it can be extended with a margin and folded over the entire movement range of the front lens group 1 and the rear group lens L2.

Also, to briefly explain the finder block 2 shown in Figure 1, the finder unit 8 and strobe device 9 are as follows:
The viewfinder field of view is changed in conjunction with the change in the focal length of the lens barrel block 1, and the illumination angle (light intensity) of the strobe is
It changes the The power source for this is the gear 15 of the 8 cam ring 14 in which the zoom motor 5 is used.
A nion 50, which is different from the above-mentioned binion 7, is meshed with the pinion 7, and the shaft 51 of this binion 500 is extended to the rear of the base plate 6, and a reduction gear train 52 is provided at the rear end thereof. The lowest gear 52a of the reduction gear train 52 meshes with a rack 53a of the cam plate 53. The cam plate 53 is slidable in the left-right direction, and a rack 53a is integrally provided at the tip (lower end) of a lower bent portion 53b at the rear end. The reduction gear train 52 decelerates the rotation of the gear 15 and reduces the movement of the cam ring] 4 to apply it to the cam plate 53.

The cam plate 53 has a variable magnification cam groove 55 for the finder device 8.
, a parallax correction cam groove 56, and a strobe cam groove 57 for the strobe snow making 9.

The lens system of the finder M8 basically consists of a fixed subject-side lens group L3, an eyepiece lens L4, and a movable variable magnification lens group L5. Variable magnification lens group L5
The angle prism P1 extends onto the optical axis only during close-up photography to particularly correct parallax. In other words, in a lens-shutter type camera, parallax is unavoidable and the amount of parallax affects the close-up shooting function, but the camera of the present invention is capable of close-up photography, and at this time the amount of parallax becomes large. Only when photographing, a wedge-shaped deflection prism P1 that is thick at the bottom and thin at the top is inserted into the optical path to bend the optical path downward so that a portion closer to the photographed area can be observed.

In addition, the strobe device 9 narrows down the irradiation angle as the focal length of the photographing lens becomes longer, that is, as the lens extends.
During close-up photography, the illumination angle is conversely widened to reduce the amount of light to the subject. Therefore, in this embodiment, the Fresnel lens [6] is fixed, and the reflective shade 59 holding the xenon lamp 58 is moved in the optical axis direction.

"Effects of the Invention" According to the autofocus camera according to the present invention, it is possible to improve the distance measurement accuracy during close-up photography. You can still sell sharp photos. The close-up shooting function is widely used in -lens reflex cameras, but according to the present invention, it can be easily incorporated into inexpensive lens-shutter autofocus cameras, and it can achieve focusing accuracy that is qualitatively equivalent to that of single-lens reflex cameras. It is possible to obtain This is particularly effective for cameras with built-in long focal length lenses that have a shallow depth of field and tend to be out of focus.

In the present invention, the short-distance correction optical element is provided at the tip of the swingable correction flag, and this element is connected to the rotation of the drive ring that shifts the photographing optical system from normal photography to close-up photography. Since the short-distance correction optical element provided in the correction flag extends to the front of the light receiving section, distance measurement for close-up photography can be performed automatically without requiring special operations.

[Brief explanation of the drawing]

Fig. 1 is a conceptual perspective view of the main elements showing an embodiment of the lens-shutter camera of the present invention, and Fig. M2 mainly shows the lens barrel block, the light emitting part and light receiving part of the distance measuring device, the short-range correction optical element, FIG. 3 is a plan view of FIG. 2, FIGS. 4 and 5 are sectional views taken along the lines ■-■ and v-v of FIG. 2, respectively. Figure 6 is a longitudinal sectional view of the lens barrel block, Figure 7 is a developed view of the front group cam groove and rear group cam groove of the cam ring, Figure 8 is an exploded perspective view of the lens barrel block, and Figure 9 is the invention of the present invention. 10 is a sectional view showing the details of the close-range correction optical element in FIG. 9, FIG. 11 is a front view of 10, and 12 Figure 13 is a sectional view showing the basic configuration of a two-group zoom lens, Figure 13 is a sectional view showing the configuration of a distance measuring device, and Figure 14 is a sectional view showing the configuration of a conventional focus correction method for close-up photography. be. DESCRIPTION OF SYMBOLS 1... Lens barrel block, 3... Light emitter, 4... Light receiver, 4e... Short distance correction optical element, 5... Zoom motor, 20... Zooming cam groove for front group , 2Of...
・Macro feeding section, 209...Macro mouth end fixed section, 4
2... Correction flag, 43... Interlocking protrusion, 44...
Advance protrusion, 46...Tension spring. Patent Applicant: Asahi Optical Industry Co., Ltd. Figure 2 Figure 3 Figure 4 Figure 5 LI L2 Figure 6) -61÷62-F-63-( Figure 7 Figure 8 Figure 9 Figure 10 Figure 4 Fig. 11 1.1 Oblique 2nd group Fig. 13 Fig. 14

Claims (2)

[Claims] (1) A distance measuring optical system based on the triangular distance measuring principle, which has a light emitting section that emits distance measuring light toward the subject and a light receiving section that receives reflected light from the subject; distance measuring from this distance measuring optical system. In an autofocus camera capable of close-up photography, the photographing optical system is equipped with a photographing optical system that is driven to a focal position based on data, and the photographing optical system is further extended by a certain amount in whole or in part during close-up photography. A driving ring of the photographing optical system that transitions between normal photography and close-up photography by rotational operation; and a light-emitting part and light-receiving part of the distance-measuring optical system when placed in front of the light-receiving part of the distance-measuring optical system; a short-distance correction optical element that optically extends the baseline length between the light-emitting part and the light-receiving part and intersects the optical axes of the light-emitting part and the light-receiving part at a finite distance; , a correction flag whose proximal end is pivoted to move the short-distance correction optical element forward and backward in front of the light-receiving unit as it swings; a spring means for biasing the drive ring in a direction in which the correction flag is rotated against the spring means when the drive ring is rotated to the close-up photographing position, and the close-range correction optical element is positioned in front of the light receiving section; An autofocus camera capable of close-up photography, characterized by comprising interlocking means provided between the drive ring and the correction flag. (2) In claim 1, the short-distance correction optical element has two fully anti-oblique surfaces, and moves the incident light in parallel in the direction of the base line length to optically extend the base line length. An autofocus camera that is a total internal reflection prism.