JPS5910913A - Focus detector - Google Patents

Abstract

PURPOSE:To perform always satisfactory focus detection even if a focal length changes by providing an optical path splitting means in the optical path of the optical image-forming system of a zoom lens. CONSTITUTION:An image-forming optical system is constituted of an image- forming lens 6 from a focusing lens 1 and an optical path splitting means 4 is provided on the optical path. Powers are reversely varied by a compensator 8 and a variator 9 cooperatively with zooming by a variator 2 and a compensator 3, whereby the focal length constituted of 1, 2, 3, 4, 8, 9, 10 forming an optical system for focus detection is made constant irrespectively of the zooming of the image-forming optical system. As a result, even if the zoom lens is zoomed to the telephoto end after the focus is detected at the wide angle end, the deviation in the depth of field is obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device for an imaging optical system, and relates to a focus detection device for an imaging optical system. The present invention relates to a focus detection device that detects the focus of an imaging optical system by comparing outputs from each arranged light receiving element.

Conventionally, the focus detection device described above has relied on changes in the convergence point distance of the light-receiving element optical system. In particular, when the photographic optical system is a zoom lens, the detection accuracy is good at the telephoto end, but the detection accuracy deteriorates at the wide-angle zoom position because the depth of focus becomes deep. For example, if you perform focus detection at the wide-angle end and then zoom toward the telephoto end, the object that is within the depth of focus at the wide-angle end may be outside the depth of focus at the telephoto end, resulting in a blurred image. There was a drawback.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device that can always perform excellent focus detection even when the focal length of an imaging optical system changes.

The feature of the configuration of the focus detection device for achieving the object of the present invention is that an optical path splitting means is provided in the optical path of the imaging optical system, and the direction of the light beam split by the optical path splitting means is different from that of the imaging optical system. A detection optical system is provided, and a point distance changing means for changing the focal length in accordance with a change in the focal length of the imaging optical system is provided in the focus detection optical system, and a point distance changing means is provided in the focus detection optical system, and a point distance changing means is provided in the focus detection optical system, and a point distance changing means is provided in the focus detection optical system to change the focal length according to a change in the focal length of the imaging optical system. A light-receiving element is disposed at a position that is coextensive with at least two positions, the planned image-forming plane of the imaging optical system and the position of its optical axis A, and the output from each of the light-receiving elements is used to combine the images. This is to perform focus detection.

It is favorable for history because it can be done. In order to better achieve the object of the present invention, the zooming action of the imaging optical system by zooming and the zooming action of the focal length changing means should be approximately inversely reversed. is friendly.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic diagram of the optical arrangement of the focus detection device of the present invention.

In the figure, 1 is a focusing lens, a variator with a double magnification function, 3 a convencator with an image plane correction function,
4 is an optical path splitting means, 5 is an aperture, 6 is an imaging lens, and 7 is a film surface which is a planned image formation surface.

The focusing lens 1 to the imaging lens 6 constitute an imaging optical system.

8 and 9 are optical systems for variable magnification, 8 is a compensator that has an image plane correction function, 9 is a variator that has a variable magnification function, 10 is an imaging lens, and 11 is a splitting prism for focal point 4 and aperture, which divides the light beam. is divided into three directions, 1]. Then, in the direction divided into three directions, there are light receiving cables 12a, 12b,
12C is placed in it. The j-ammonium element extending from the above-mentioned Zen Pen Setter 8 to the splitting prism 11 constitutes a base for focusing.

FIG. 2 is an explanatory diagram of the II (! principle) of the focus detection device of the present invention. L is the imaging lens, F is the expected image formation ff+i, Pl is the defocus position 1^1 on the 9 side, and P2 is the image formation lens. The side focus positions are shown respectively.In Fig. 1, when the position of the light receiving element 12b is set to the position where it is aligned with the planned image forming plane F of the imaging optical system, the position of the light receiving element 12a is P1, The position of the light receiving element 12C corresponds to P2.

The blur width of the imaging optical system is detected by the light receiving elements 12a, 12b, and 12c in FIG. 1, and the light receiving elements 12a, 12b
, 12c, the focus of the imaging optical system is determined by comparing the outputs of the images.

When the outputs of the light-receiving elements 12a and 12C match and the output of the light-receiving element 12'b is higher than the outputs of the light-receiving elements 12a and 12c, the object is in focus, and otherwise it is considered to be out of focus.

In Figure 1, when zooming the photographing system, the film surface 7
The focus movement amount changes in proportion to the square of the magnification ratio. If the focal length of the focus detection optical system is constant, the amount of focus movement in the light receiving elements 128.degree. 12b, 12C also changes in proportion to the magnification ratio. 31st W(a)
, (b) and (c) are light receiving elements 12a and 12, respectively.
The changes in the output S at points b and 12c are shown in comparison with the amount of movement lz of the focusing lens 1 on the horizontal axis. (-1, (b).

(c) shows how the amount of movement ΔI of the focusing lens l increases corresponding to the zoom position at the wide-angle end, intermediate focal length, and telephoto end of the imaging optical system, respectively. Even for the same amount of movement of the focusing lens 1, the output S changes depending on the zoom position. This is because the depth of field changes depending on the focal length. For this reason, when zooming to the far side after focusing at the zoom position on the wide-angle side, the depth of field becomes narrower due to zooming, so the focus position may be off. Therefore, regardless of the zooming of the imaging optical system, the light receiving elements 12a, 12b,
It is desirable to keep the accuracy of focus detection at 12c constant so that focus detection can always be performed within the depth of field at the telephoto end.

As a means of overcoming this, as shown in Fig. 1, the variator 9 and convencator 8 for changing the magnification of the focus detection optical system are moved in conjunction with the zooming by the variator 2 and convencator 3. It is better to reduce the magnification effect. 1 in Fig. 1, which is reversely magnified by the convencator 8 and variator 9 and becomes a focus detection optical system.
2.3.4.8.9.10 is to be made constant regardless of zooming of the imaging optical system. Does this result in focus detection at the wide-angle end? Even if you zoom to the telephoto end after reaching T, you will not miss the depth of field. −
According to Rikiki's invention, the focus detection optical system has a zoom function, thereby making it possible to change the field of view range for distance measurement in accordance with the focal length of the imaging optical spear. Therefore, when the focus detection optical system has a constant focal length, the distance measurement field of view with respect to the photographic screen does not change even if the imaging optical system is zoomed. When the imaging optical system is wide-angle, objects near and far are often mixed in the photographing Di1, so if the field of view for distance measurement is large, competition between distance and distance will occur, resulting in a decrease in distance measurement accuracy. - Furthermore, when the imaging optical system is telephoto, the angle of view is narrow, so the field of view for distance measurement becomes small, making it easy to miss the range of field of view for distance measurement due to camera shake, etc. For this reason, in the case of a wide angle, it is better to have a smaller distance measurement field of view.
On the other hand, in the case of a telephoto lens, the larger the field of view for distance measurement, the better. Therefore, if the distance measurement field of view does not change by zooming the imaging optical system, problems will occur on either the wide-angle side or the telephoto side. Figure 4 (a), (bl, (c)
) is a diagram showing the distance measurement field of view range with respect to the photographing range, and the shaded area indicates the distance measurement field of view. Figure 4 (,) is a wide-angle shot.
ll The distance field of view is wide, which eliminates situations where near and far conflicts are likely to occur.

(b) and (c) show that the range of the distance measurement field of view is as large as the standard FA in wide-angle photography and telephoto photography, respectively.

In the present invention, it is possible to configure the imaging optical system 111 group so that the composite focal length of the focus detection optical system is constant at red, which is independent of the zooming of the imaging optical system, and the distance measuring unit #f performs zooming. This makes it possible for the lens to change relatively, making it smaller at the wide-angle end and thicker at the telephoto end. In other words, the distance measurement field of view is the 41st field of view according to the wide-angle rule 1. J(b), and on the telephoto side, it becomes as shown in FIG. 4(c). If the focus detection optical system does not have a zooming effect, it is not preferable because it becomes like the one shown in FIG. It should be noted that the focus detection optical system does not necessarily require a zoom function, but may simply be one whose focal length changes depending on the focal length of the imaging optical system.

In the river fish detection device according to the present invention, it may be difficult to find the moving direction of the imaging optical system focusing lens. In such a case, if the distance of the focal point of the focus producing optical system is appropriately selected, it is possible to always compare the outputs of the light receiving elements as shown in Fig. 3(b), so the movement direction of the focusing lens can always be detected. I can do it. Therefore, the first stage of focus detection is to set the focus detection optical system to the short focus side, and after detecting the ζ direction, the focus detection optical system is zoomed for precision.

It is also possible to perform focus detection.

In the above embodiment, the photographing system is a zoom lens, but a telephoto lens in an interchangeable lens type camera,
Exactly the same thing can be considered for wide-angle lenses, and the present invention can be effectively applied.

As described above, according to the present invention, it is possible to obtain a focus detection device that can always perform excellent focus detection even if the focal length of the imaging optical system changes. Furthermore, since it is possible to obtain an optical system in which the area of the distance measuring section on the subject side remains approximately the same even when the focal length of the imaging optical system changes, this is not only advantageous for focus detection, but also allows the viewfinder image to be seen with the naked eye. It is also advantageous when measuring distance.

Next, numerical examples of the present invention will be shown. In the numerical examples, the radius of curvature of the 1st fr lens surface in order from the object side, D
i is the lens thickness and air gap at the first scan in order from the object side,
Ni and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

However, Ri, Di, Ni, ν related to the focus detection optical system
1° is from the optical path splitting means to
Iol + N101 eν101.

Numerical Example 1 Photographing optical system f=8.711 to 24.779 FN
o, l: 113~14 are half prisms, 15th surface is aperture R1 = 112.03 DIJ, QQ
N1=1.80518 ν1=25.4R2=
3726 D2=7.52 N2=1.
58913 ν2= 61.0R3-~76.41
D3-0.12R4=25.08
D4=4.51 N5=1.62299
ν3=58.2R5=67.9006-variable R6=-953,36D 6=0.90 N
4=1.58913 C4=61.0R7=
11.47 D7=3.24R8=-1
9,41D 8=0.72 N5=1.5891
3 ν5= 61.0R9= 14.17
D9=2.69 N6=1.80518
Shiro = 25.4R10 = 7:? 77 DIO
=Variable Rtt=27.54 D11=2.6
8 N7 two t, 58913 shift = 61.0R
12=-10751D12-Variable R13=0.0 D13=7.00 N8
=1.51633 shi8264. lR14=
0. OD14=0.50R15=0.0
D15=2.60R16=33.89
D16=2.24 N9=1.77250 ν
9=49.6R17=-8618,08D17=0
．． l0R18=21.22 D18=2.6
5 Nl0=1.77250 Silα=496
R19=-317,31019=1.13R20=
-17,76D20=5.03 N11=1
．． 80518 ν11=25.4R21=
17.05 D21=3.86R22=84
．． 74 D22=5.22 N12=1.772
50 Shi12-49.6R23= -15,3
6D23=0.07R24=14.31D
z4 = 46g Nl = 1.77250 sill
Treasure=496R25=-21,14D25=0.6
0 N1 piece = L80518 Sil 254R2
6 = 67.66 b, f = 7.95 Focal length from 16th to 26th plane...13942 Focus detection optical system f = 14.03S-A9.982 FNo., 1
+ 2~2,5RIO1= 103.69 Dl
ol;1. OON101=1.80518 ν10
1=25.4R102=36.80D102
=3.0ON102-1.58913 C102.
=61.0ato3=-90,86oto3=o,
tz lR104= 27.11
D104=2.50 N103-1.58913
νlO~61,0R105= 123.98
D105=variable lR106=-921
, 15D106: (1,90 NIO small = 1.62299
10 volumes = 582R107 = 11.49
D107 338 1R108= -
18,12D108-0.90 NIO 1.51
633 ν10ren64. lR109=15.
29 D109=2.63 NIO Jin 1.805
18 Shi106=25.43110=76.1
4 DIIO-variable 1°R111=
34.96 D111=2.56 N107=
1.58913 Shi107=61.0R112=
-69,15D112-0.20 1R
113=55.75 0113=2.60
N10B=L80610 ν101#40.9R1
14=-53,54Dl14. , +1.26
1R115=-13,83D115-1.
00 NIO stirring 1.62004 Shi10 stirring 36
3R116=19.95 D116=3.4
6 1R117= 37.63
D117=4.0ONilα=1.77250 Shi11ω=496R11B= -16,21Dl182010 1R119= 16.61 D11
9-=4.00 N111=1.61484
ν111=51.2R120=-13,17DI2
+'l=1.00 N112-1.71736
J/112-29.5R121 = 23.70 (Wide-angle end) (Telephoto end) b, f, =, 21.80 3 Composite focal length of the front group focus detection optical system of the imaging system

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical arrangement embodying an embodiment of the present invention. FIG. 2 is an explanatory diagram of the principle of the focus detection method of the present invention. FIG. 3 is an explanatory diagram showing changes in output values from each light receiving element of the focus detection device according to the present invention. FIG. 4 is an explanatory diagram showing the relationship between the photographing range and the distance measurement visual field range in the present invention. FIG. 5 is a sectional view 1 of an optical system according to an embodiment of the present invention. In the figure, 1 is a four force single lens, 2 and 3 are variable power systems, and 4
1 is an optical path exposing means, 6 is an imaging lens, 8 and 9 are variable magnification systems, 1
1 k, t split prism, 12a, 12b. 12e is a light receiving element. Patent applicant: Canon Co., Ltd. Atsushi / 2 Figure 2

Claims (1)

Scope of Claims: (1) An optical path dividing means is provided in the optical path of the imaging optical system, and a focus detection optical system different from the imaging optical system is provided in the direction of the light beam divided by the optical path dividing means; The focus detection optical system is provided with a focal length changing means for changing the focal length in accordance with the change in the focal length of the imaging optical system, and the optical axis -F of the focus detection optical system is an optical axis -F of the focus detection optical system. A light-receiving element is arranged at a position that is coincident with at least two positions of a planned image-forming plane of the optical system and a position on its optical axis, and focus detection is performed using the output from each of the light-receiving elements. L+! A focus detection device that detects f-character. (21+3? The focus detection device according to claim 1, characterized in that the imaging optical system and the focal length changing means are constituted by a zoom lens. (3) +] By ill-consolidated imaging optical system zooming 3. The focus detection device according to claim 2, wherein the zooming action and the zooming action by the zooming of the focal length changing means are inverse zooming actions.