JPS62264030A - Auto-focus camera capable of close photographing - Google Patents

Abstract

PURPOSE:To improve the precision of range finding for close photographing to ideally focus a camera by arranging an optical element which optically extends the base line length between a light projecting part and a light receiving part in a range finding optical system to allow their optical axes to intersect each other in a finite distance. CONSTITUTION:The optical element is arranged which is moved forward to the front of the range finding optical system for close photographing and optically extends a base line length L between a light projecting part 3 and a light receiving part 4 in the range finding optical system to allow their optical axes to intersect each other in a finite distance. This optical element has two total reflection faces and is a total reflection prism 7 which moves an incident light in parallel with the direction of the base line length L to optically extend this length L. When the prism 7 with a mask 8 is arranged in the front of the light receiving lens 4, that is, close photographing is performed, the first group of a photographic lens is fed out by a certain extent other than by which the first group is fed out by an auto-focusing device. Thus, a measurable range finding area is shifted to the close distance side to improve the precision of range finding and the camera is correctly focused.

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, before explaining the present invention, the relationship between the object distance and the amount of extension of the two-group zoom lens will be described. FIG. 4 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/f++f+/X) +HH+Δ・
...■ However, U: Subject distance f, : Focal length of M1 group , X-(-2fl-HH-A+U-JC2f1-HH◆△
-U)2-4ft 2)/2...■.

On the other hand, FIG. 5 shows the relationship between the object distance MU of the distance measuring optical system (apparatus) based on the triangular distance measuring principle and the amount of deviation t on the position detection element 2.

The triangulation distance measuring device includes a light source 1, a position detection element 2 (for example, a PS
D) It is composed of a light projecting lens 3 and a light receiving lens 4, and the distance to the subject is detected by obtaining the reflected light from the subject of the light emitted from the light source 1 with the position detection element 2. In other words, the distance M from the film surface 5 to the subject
The amount of deviation t of the light source image on the position detection element 2 with respect to U (the reference is the position M of the light source image when the subject is infinite) is expressed by the following equation.

t=L-f/(U-f-d) -... ■However, L:
Baseline length f of the distance measuring device: Focal length d of the light-receiving lens; 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 2, as is well known. Therefore, if the photographing optical system is moved to the focal position based on the above equations (1) and (2) using this amount of electricity, focusing will be achieved automatically. Such an autofocus camera and a drive mechanism for a photographing optical system are well 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 photographic optical system shown in Figure 4, the first group of photographic lenses is
A fixed amount is delivered in addition to the amount delivered by the autofocus device.

Figure 6 shows the distance that can be measured by the distance measuring device Mii! This is a conventional example in which the range is shifted to the short distance side. As shown in the figure, by arranging a prism 6 having an apex angle of θ in front of the light-receiving lens 4, the measurable range M can be shifted to the short distance side.

When the apex angle of the prism 6 is θ and the refractive index is n, the shift of the light source image on the position detection element 2 with respect to the object distance U1 is
+ can be found using the following procedure.

The angle of incidence α of the light beam onto the object-side surface of the prism 6 is determined by the following equation.

a=tac'(L/(υ, -f-a))+θ When a ray of light strikes a person at an incident angle α on a prism having an angle θ, the deflection angle β is determined by the following equation.

β=α-θ+5in-'[n 5in(El-5in
(a/n))] Therefore, ]γ=α−e− β Furthermore, the amount of shift t1 of the light source image on the position detection element 2 is t+=
It becomes f-tany. LJmf is the subject distance when the optical axis of the projection lens 4 and the ray of light intersect with the optical axis of the projection lens 3, and if the thickness of the prism 6 is ignored, Umf+=
L /1an(sin-'(nsinθ)-θ)f+
Expressed by d.

Here, as an example, the photographing optical system is a two-group zoom lens,
Focal length of the first group: 811 f + = 24.68 mm,
Principal point interval HH = 7.02 mm, interval Δ 30.04 mm between the focal position of the first group and the focal position of all groups, interval d between the film surface and the focal plane of the light receiving lens = 6, 292 mm-
Shift amount of M1 group during close-up shooting: 0.5502 mm, base line length of distance measuring device L = 30 mm, focal length of light receiving lens N
f・20mm, prism 6Q apex angle θ=2.826°, refractive index of the prism n・1.483, photographable distance range is 0.973m-■, number of extension steps is 18 steps, of which 0
．． The calculation results for the case where the shooting range of 0.973m to 6m is shifted to the shooting range of 0.580m to 1.020m by prism 6 in the case of having a feeding mechanism that divides 973m to 6m into 17 steps. It is shown in Table 1.

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

(Left below) LI+@f+1.283m From the results in Table 1, it can be seen that with the correction using prism 6, the position detection element 2
It can be seen that a deviation of 0.027 mm occurs at the top. 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 advance directly based on the output of the position detection element 2, the photographing lens cannot be moved to the correct in-focus position, resulting in a blurred photograph.

In other words, with only correction using prism 6,
This is because the rate of change of the shift amount t of the light source image on the position detection element 2 with respect to the subject distance 111u+ cannot be changed, so complete correction is impossible.

[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.

“Summary of the Invention” The present invention is based on +7-
The amount of change in t from 18 to O-1 is 0.5334 mm5
Since the amount of change in it is 0.4794 mm, complete correction is possible by increasing the amount of change in t by 0.533410.4794 times, that is, I + 130 times during close-up photography. For this reason, the present invention advances to the front of the distance measuring optical system during close-up photography, and measures the base line length between the light emitting part and the light receiving part of the distance measuring optical system optically (
It is characterized in that an optical element is arranged so that the optical axes of the light emitting part and the light receiving part intersect with each other at a maximum distance.

Embodiments of the Invention FIG. 1 shows the configuration of a distance measuring device for an autofocus camera according to the present invention during close-up photography.

The prism 7 and the mask 8, which have two fully anti-slanted surfaces and are arranged in front of the light-receiving lens 4 of the distance measuring device, are retracted when not in close-up photography.

The prism 7 has the effect of optically extending the base line length of the distance measuring device and the effect of refracting light rays. FIG. 2f shows a detailed top sectional view of the prism 7, mask 8, and light receiving lens 4, and FIG. 3 is a front view of FIG. 2. Mask 8 is
It is for blocking light other than the necessary optical path, and has an aperture 8a on the subject side and an aperture 8b on the light receiving lens 4 side. The aperture 8a is opened in the shape of a slit and is spaced apart from the optical axis O of the light emitting lens 3 by a distance l from the optical axis O of the light receiving lens 4. It is opened in a slit shape to correspond to the

When the prism 7 with the mask 8 is placed in front of the light-receiving lens 4, that is, during close-up photography, the first lens group of the photographing lens is extended by a fixed amount apart from the amount extended by the automatic focusing device. It is configured. By arranging the prism 7 in front of the light receiving lens 4 as shown in FIGS. 1 and 2, the measurable distance H range can be shifted to the short distance side. The prism 7 optically extends the baseline length to L-11 by translating the light beam incident thereon by l in the direction of the baseline length.

If the angle we of this prism 7 is, the refractive index is n, and the amount of parallel movement of the light beam is l as described above, then the object distance MLJ
The amount of deviation t2 of the light source image on the position detection element 2 with respect to 2 is:
You can find it using the following steps:

can.

The angle of incidence α of the ray of light on the surface of the prism 7 on the subject side is obtained from the following equation.

a +=tan-'((L+ 42 )/(U2-f-
d)) Conflict θ.

This equation means that the base line length of the triangulation distance measuring device has been extended from before the prism 7 is inserted to L+β after insertion.

When a ray of light enters a prism with an angle θ1 at an incident angle α, the deflection angle β can be obtained from the following equation.

β1・α1-e, ◆5in-' [n5in(θ word-5
in(α,/n))], γ5・α, −θ, −β1 Therefore, the amount of shift t2 of the light source image on the detection element 2 is t,
=ftany+, U, f2 is the subject distance when the optical axis of the light receiving lens 4 and the ray of light intersect with the optical axis of the light emitting lens 3,
If the thickness of prism 7 is ignored, U wlp2 (Li
)/1an(sin-'(nsinθ,)-8+
)"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 f + = 24.68.
mm, principal point distance H) I = 7.02 mm, distance between the focal position of the first group and the focal position of all groups = 30.04 mm, distance d between the film surface and the focal plane of the light receiving lens 6.292 mm
.

Shift amount of the first group during close-up shooting: 0.5502 mm, base line length of distance measuring device: 30 mm, focal length of light receiving lens Mf□
20 mm, angle e of prism 7, = 3.39°,
Refractive index n = 1.483, amount of parallel movement of light ray 42 = 3
．． 39mm, shooting distance 11HI! The circumference is 0.973m
-co has 18 stages, of which 0.973m
If you have a feeding mechanism that divides ~6m into 17 stages,
Shooting speed of 0.973m to 6m with Prism 7
．． Table 2 shows the results of calculations performed for the case where the shooting speed is shifted to 580 m to I and 020 m.

(Margin below) From the results in Table 2, the difference between each stage of the light source image on the position detection element 2 during normal shooting and close-up shooting is ±Q, OQ01mm
It can be seen that it is suppressed to below. Therefore, if the photographing optical system is controlled in accordance with the output of the M detection element 2, it is possible to obtain a photograph with almost perfect focus. The length is optically 1.113 times that of normal shooting (30mm → 3
3.39 mm), indicating that the amount of movement on the position detection element 2 could be increased by 1.113 times.

"Effects of the Invention" According to the automatic focusing camera according to the present invention, distance measurement accuracy during close-up photography can be improved. You can sell photos that are sharp and in focus. The close-up shooting function is widely used in -lens reflex cameras, but according to the present invention, it can be easily incorporated into an inexpensive autofocus camera with a set of lens shutters, and it can achieve focusing accuracy substantially equivalent to that of a single-lens reflex camera. It is possible to obtain. This is particularly effective with cameras equipped with long focal length lenses, which have a shallow depth of field and can easily cause blurring.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a focus correction system during close-up photography according to the present invention, and FIG. 2 is a cross-sectional view showing details of the prism section and light receiving lens section of FIG. M1. FIG. 3 is a front view of FIG. 2. Figure 4 is a sectional view showing the basic configuration of a two-group zoom lens, Figure 5 is a sectional view showing the configuration of a distance measuring device, and Figure 6 is a configuration of a conventional focus correction method for close-up photography. FIG. 1...Light source, 2-Position detection element, 3...
Emitter lens, 4.-Receiver lens, 5.-Film surface,
7.-Total reflection prism, 8...Mask No.1 Fig.2a Fig.3 Michibe Uga, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 108279, filed in 19882) Title of the invention: Auto-focus camera capable of close-up photography 3, person making corrections Relationship with the case Patent applicant residence Address: 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (052) Asahi Optical Co., Ltd. Representative Matsumoto
Toru 4, Agent address: 501 Yonbancho Heights, 3-1 Yonbancho, Chiyoda-ku, Tokyo 102 2! ! 03(234)0290
Name (8328) Patent attorney Kunio Miura (2 others) (1) In the first line of page 3 of the specification, X = (-2f I-HH-Δ+U-J (2f + ◆H
H◆△-U)2-4f + 2) /2 is written as X=(-2f+-HH-Δ +U-+" order -
Correct it as U −4f+ )/2. (2) The phrase “Piboke” on page 8, line 8 of the specification should be replaced with “
"Out of focus" is corrected. (3) In the first line of page 15 of the specification, the word “tokuni” should be replaced with “
Especially,” he corrected. that's all

Claims (2)

[Claims] (1) Equipped with a distance-measuring optical system based on the triangular distance-measuring principle and a photographing optical system that is driven to the focal position based on distance measurement data from this distance-measuring optical system. , in an autofocus camera capable of close-up photography in which all or part of the optical system is further extended by a certain amount, the light emitting section of the distance-measuring optical system is extended to the front of the distance-measuring optical system during close-up photography. An autofocus camera characterized in that an optical element is arranged to optically extend the baseline length between the light emitting part and the light receiving part, and intersect the optical axes of the light emitting part and the light receiving part at a finite distance. (2) In claim 1, the optical element is a total reflection prism that has two totally anti-oblique surfaces and that moves incident light in parallel in the direction of the base line length to optically extend the base line length. An autofocus camera characterized by: