JPS5910912A - Focus detector - Google Patents

Abstract

PURPOSE:To detect focus always with specified accuracy even if the size of the stop in the optical path of an image-forming optical sytem changes by providing an optical path splitting means just before the stop. CONSTITUTION:An optical path splitting means 2 having a half mirror is provided just before a stop 3 of an image-forming optical system. If a photodetector 8b is placed in the position corresponding to the intended image-forming plane F of the image-forming optical system, the position of a photodetector 8a corresponds to P1 and the position of a photodetector 8c to P2. The out of focus width of the image-forming optical system is detected with the photodetectors 8a, 8b, 8c, and the focusing of the image-forming optical system is judged from the comparison in the outputs of the photodetectors 8a, 8b, 8c. The case in which the outputs of the photodetectors 8a and 8c coincide and the output of the photodetector 8b is higher than the output of the photodetectors 8a and 8c is determined to be in focus and the other cases are determined as out of focus.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device for an imaging optical system [2] Particularly, the present invention relates to a focus detection device for an imaging optical system. Comparing the outputs from the light-receiving elements of the J'L ICs arranged in the J'L IC (this relates to a focus detection device that detects the focus of the imaging optical system using the IC).

Conventionally, in the above focus detection device, the optical path splitting means for guiding the light beam to the light receiving element was placed in the optical path of the imaging optical system and behind the aperture, so the focus detection accuracy was lower than that of the aperture of the imaging optical system. It depended on size.

In particular, there was a drawback in that focus detection accuracy changed when the size of the aperture changed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device that can always perform focus detection with constant accuracy even if the size of the aperture of an imaging optical system changes.

The feature of the structure 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 just before the aperture, and the imaging optical system is directed in the direction of the light beam split by the optical path splitting means. The gold coating of the focus detection optical system, which is different from the focus detection optical system, is located on the optical axis of the focus detection optical system and at a position that is co-readable with at least two positions of the expected imaging plane of the imaging optical system and a position on the front axis thereof. A light-receiving element is arranged respectively, and the output from each of the light-receiving elements is used.
C. Focus detection is performed.

A detailed explanation of the present invention will now be given according to the figures.

FIG. 1 is a schematic diagram of the optical arrangement of the focus detection device of the present invention. In Fig. 1, 1 is the front group of the imaging optical system, 2 is...-
3 is an aperture of the imaging optical system, 4 is a rear group of the imaging optical system, 5 is a film surface which is a planned imaging surface, 6 is an optical system for focus detection, and 7 is for focus detection. This is an optical path splitting prism that splits the light beam into three directions. And three light receiving elements 8a are provided in three directions.

8b and 8c are placed? are doing.

In the embodiment of the present invention, when three light-receiving elements are arranged, all oil is used, but the number is not necessarily limited to three, and two or four or more can be used depending on the purpose.

FIG. 2 is an explanatory diagram of the principle of the focus detection means of the present invention.
L indicates an imaging lens, F indicates a planned image forming surface, Pl indicates a defocus position on the object side, and P2 indicates a defocus position flk on the image side. In FIG. 1, when the position of the light receiving element 8b corresponds to the expected imaging plane F of the one-quadrant optical system, the position of the light receiving element 8a corresponds to Pl, and the position of the light receiving element 8c corresponds to P2. .

The blur 11 of the imaging optical system is detected by the light receiving elements 8a, 8b, '8c in FIG. 1, and the focus of the imaging optical system is determined by comparing the outputs of the light receiving elements 8a, 8b, 8c.

The outputs of the light-receiving elements 8a and 80 match, and the light-receiving element 8b
When the output is higher than the output of the light-receiving elements 8a and 8c, the image is in focus, and otherwise it is considered out of focus.

FIG. 3 is an explanatory diagram showing changes in the output of the light receiving element with respect to the amount of defocus. The horizontal axis represents the amount of movement Δx' of the focus section of the imaging optical system, and the vertical axis represents the amount of movement of the focus section of the imaging optical system, and the vertical axis represents the amount of movement of the focus section of the imaging optical system.
, 8c. If the light-receiving element surface matches the image-forming surface, the output will be at its peak, and the output will decrease as it deviates? show. The focus detection optical system is an ideal imaging system, and between the light receiving elements 8a and 8Lt and between the light receiving elements 8b and 8c.
- The optical path length between the two is the same. Light receiving cable 8b is planned.
゛When aligned with the image plane F, the light receiving elements 8a and 80
The outputs obtained from the light-receiving elements 8a and 8c do not match if the output 8b does not match the expected imaging plane F. Therefore, by comparing the outputs of the light receiving elements 8a and 8c, it is possible to determine whether or not focus is achieved. However, even in the case of large defocus, the outputs from the light receiving elements 8a and 80 are almost the same, and it appears that the light is in focus, but the light receiving element 8
The output b indicates the peak value when in focus and becomes low when defocused, so when the outputs of the light receiving elements 8a and 8c match, it is possible to determine whether or not the focus is achieved by the magnitude of the output of the light receiving element 8b. .

Moreover, FIG. 4 shows the beam diameter A of the focus detection optical system.

This is a diagram showing changes in the output of the light receiving element corresponding to H. The horizontal and vertical axes are the same as in FIG. The outputs from the light receiving elements 8a and 8c for the luminous flux A are A+ and At at the valleys, and the output from the light receiving element 8a for the luminous flux B.

The output from +38c becomes B+, B2. The accuracy of focus detection depends on the difference in the absolute values of the output values from the light receiving probes 8a, 8b, and 8c at a certain point in the focus section of the imaging optical system. 1 When using the light flux from the bright part of the imaging optical system, that is, the light flux sound of A in the M2 diagram, the output values from the light receiving elements 8 a' and 8 c at a certain point x1 are Ar and Ar.
becomes. Also, when using the luminous flux B sound, Br, B7
becomes. Since focus detection is performed using the difference between the output values from the light receiving elements 8a and 8c, (AI'A2') is better than (AI'A2').
It is clear that this is larger than Bl'B2'>. For this reason, focus detection accuracy is better when focus detection is performed using the light beam Ak.

In other words, as shown in Fig. 4 A+ and A2, the output t changes sensitively to defocus, but when the aperture is closed, the 4th
The rate of change becomes confusing as shown in Figures BI and B. Therefore, when the focus detection optical system is the same as the imaging optical system, the distance measurement accuracy changes in conjunction with the aperture of the imaging optical system. If focus detection is performed using a light beam that does not pass through the aperture, detection accuracy can always be obtained when the aperture of the imaging optical system is wide open.

In addition, in the present invention, the focal length of the rear group of the imaging optical system is /n The focal length of the focus detection optical system is /'M Pifocus shift on the film plane from infinity to close range #IJJ violet △l
(, the corresponding amount of focus movement on the light receiving element surface is /\
Since the following relationship holds true with M, the focal length ^I1
．． /M gold exchange lens or zoom lens system by changing the light receiving element-1-8a
.

It is possible to make a difference in the optical path length between 8b and 8e.

This has the merit of being able to obtain the optimum amount of focus movement. This is because if the amount of focus movement relative to the light receiving element is too small, the output change will be small and the detection accuracy will decrease.
This is because if the amount of focus movement is still too large, a large blur will appear over a wide range, making it difficult to determine the direction of the cocoon bin.

1' (1) #: 1 for i lens, F number is h゛, -D is diameter, l is focal length), but in an imaging optical system for focus detection where the aperture does not change. On the other hand, if we ask f, then F
The numbers become darker and the depth of focus becomes all urine. However, while the depth of focus is proportional to j according to the number,
Since the amount of focus movement is proportional to f2, the effect is large even if the cancellation of p force/bar is subtracted.

Also, regardless of the aperture of the imaging optical system, the aperture can be moved in and out of the focus detection optical system, so if there is a large blur, the aperture can be inserted to detect the focus, and the aperture can be roughly detected by opening the aperture. It also becomes possible to perform precise focus detection.

Therefore, it is preferable that the focal length of the focus detection optical system is longer than the focal length of the imaging optical system.

As described above, according to the present invention, focus detection can always be performed with a constant accuracy regardless of the size of the aperture of the imaging optical system. Further, by arbitrarily changing the focal length * of the focus detection optical system different from the imaging optical system, the optimum distance measuring ability can be obtained.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the first lens 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 νi are the Gance refractive index and Ambe number of the first lens from the object side, respectively.

However, the optical system is
+Di, Ni +νi are sequentially divided into valleys I by the optical path splitting means +a+ +D+o+ +N+o.

This is indicated by νIO1.

Numerical Example 1 Imaging optical system f -1 ~ 4.753 F + 7 par - 1.8 - 2.0 Hydraulic angle 2ω -42° ~ 92°a 1) νd NdR1
6,471D I-0,150shi 1-25.4 N
l-1,80518kL 2-2.689 D 2-
U, 593 p 2-61.0 N 2-1.58
913) L 3--8.183 1) 3-0
．． 011R4-2,098D 4-0.360 C3
-61.0 N 3-1.58913 5” 7
．． 249 D5)t 6-25.88
7 D 6-0.068 p 4-48.5 N
4-1.69700R7-0,863D 7-0.
2161L8--1.191 D8-0.068
5-53.2 N5-1.69350It 9-1
．． 012 D 9-0.300 Jiro 25.4
N 6-1.80518R10”-13,014Dl
o all-2,949 Dll-0,390 shear 47.1
N 7-1.623741L12”-1,374D
i2-0.068 JJ8-25.4 NM-L8
0518R13--3,288D13 R14+ (To) I) 14-0.563 ν9
-64.1 N 9-1.51633R15=
c6 Di5-0.3971L16- 4.21
1 Di6-0.203 Di10-38.0
N10-1.72342R17''~3.553
D I7-0.061R18--t671 D18-
0.103 Si1l-25.4 N11-1.80
5181L19--2.615 D19-0.8
50EL20-4.574 D20-0.103
C12-23.9 N12-1.84666K 21
- 1.190 1) 21-0.123 le 22-1
．． 526 1) 22-0.357 C13-49.
6 N13-1.77250IL 23+-2,27
2 b, f -1,625 Front 0.21 position 16-23 of 16 aperture planes Focal length of blood -2167 2 Focus detection optical string f-3,003F No. 7...
--1:2.5RD VdN
d101 1.991 0.463 48
．． 9 1.53172102-1.226
0.135 25.4 1.8051810
3 -2.718 b, f, -2,746 3 Imaging optical system front group' composite focal length of focus detection optical system

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system showing an embodiment of the present invention. FIG. 2 is an explanatory diagram of the principle of the focus detection means of the present invention. FIGS. 3 and 4 are explanatory diagrams showing changes in output values from each light receiving element of the focus detection device. FIG. 5 is a sectional view of an optical system showing an embodiment of the optical system of the present invention. In the figure, 1.4 are the front and rear groups of the imaging optical system, 2 is the optical path splitting means, 3 is the diaphragm, 5 is the planned imaging plane, 6 is the focus detection optical system, 7 is the optical path splitting prism, and 8a , 8b and 8c are light receiving elements, respectively. Patent applicant: Canon Co., Ltd. Agent: Gi Marushima -] “ ′ ”
;↓', -,,! , j

Claims (1)

[Claims] An optical path dividing means is provided in the optical path of the imaging optical system immediately before the aperture,
A focus detection optical system different from the imaging optical system is provided in the direction of the light beam split by the optical path splitting means, and a focus detection optical system different from the imaging optical system is provided on the optical axis of the focus detection optical system, and is located on the optical axis of the focus detection optical system, and is located on the optical axis of the imaging optical system. Focus detection characterized by arranging light-receiving water droplets at positions common to at least two positions on the surface and its optical axis, and performing focus detection using outputs from each of the light-receiving elements. MountingRY0