JPS6256914A - Focus detecting device - Google Patents

Abstract

PURPOSE:To simplify a lens system and to improve the image formation performance of the secondary object image by composing an image re-forming lens of two lenses which meet specific requirements. CONSTITUTION:Luminous flux from an object after passing through a photographic lens 1 forms the primary object image nearby an expected image- formation surface 3. Luminous flux S1 of the primary object image which passes through one exit pupil 2-1 of pupils 2 of the photographic lens 1 passes through a field lens 4 and one prism of a prism body and then form the secondary object image on one the surface of one photodetecting element 8-1 of a photodetecting means 8 through an image re-forming lens 7. Similarly, luminous flux S2 forms the secondary object image on the surface of a photodetecting element array 8-2. This image re-formation system has the image re-forming lens 7 consisting of the 1st lens L1 with positive refracting power and the 2nd lens L2 with positive refracting power successively from the side of the photographic lens 1. Then, the focus detection accuracy is improved by improving the image formation performance of the secondary object image while the lens system is simplified by satisfying inequalities I and II, where Ri is the radius of curvature of the (i)th lens L2, of the image re-forming lens.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a focus detection device K suitable for photographic cameras, video cameras, etc. In particular, the present invention relates to a focus detection device K suitable for photographic cameras, video cameras, etc. This invention relates to a focus detection device that detects the focal position of a photographic lens by forming a plurality of secondary object images from a luminous flux and detecting the relative positional relationship of the plurality of secondary object images.

(Conventional technology) Compared to the conventional technology, the light-receiving focus detection method has a relatively high accuracy.
There is a method called the fl-shift method, which was proposed in, for example, Japanese Patent Laid-Open No. 52-95221. The structure in which the imaging system and light receiving means are arranged is made of gold.

Among these, the mother-shaped system is a prism body in which one or two re-imaging lenses and two prisms are arranged so that the wedge angles are opposite to each other, or a part of two re-imaging lenses have refraction directions that are mutually opposite to each other. It has an optical member with an inverted prism. Further, the light receiving means Fi has two light receiving element arrays.

The re-imaging system forms two secondary object images from the primary object image on the light-receiving element array surface of the light-receiving means using the light flux that has passed through the two pupil regions of the photographing lens. The relative positions of the two secondary object images on the light-receiving means surface appear to be laterally shifted in the direction in which the light-receiving element rows are lined up depending on the focusing state of the photographing lens.

The focus of the photographing lens is detected by detecting the relative positional relationship between the two secondary object images using a light receiving means. For this reason, in focus detection using the image shift method, the imaging performance of the @secondary object image on the light receiving means surface greatly influences the focus detection accuracy.

In order to improve focus detection accuracy, a re-imaging lens having high IB fine performance with good correction of various aberrations is required. However, when trying to obtain high imaging performance, the number of lenses is t.
-The lens system must be increased in size, resulting in an increase in the size of the entire lens system.

For this reason, if kept, it becomes difficult to incorporate the focus detection device into a narrow space such as the bottom of the camera body.

(Problems to be Solved by the Invention) The present invention aims to improve the imaging performance of the secondary object image while simplifying the re-imaging lens in an image shift type focus detection device. The purpose is to provide a pointless detection device that enables detection.

(Problem t - Means for solving it) Front t! in the image plane area of the photographing lens. A re-imaging system that divides the depth of the I2 photographing lens into a plurality of regions and forms a secondary object image of fJLa from the light beam passing through the plurality of divided recitation regions.
lk arrangement, a light receiving means consisting of a plurality of light receiving element arrays is arranged near the image plane of the inner working system, and the relative positional relationship of the plurality of secondary objects is detected by the light receiving means, In the focus detection device for detecting the focal position of the photographing lens, the re-imaging system includes a first lens having a positive refractive power and a second lens having a positive refractive power in order from the photographing lens side. -3((R2+R1)/(R2-R1) (R1
)<0.7・・・・・・・−・(11-R1)<0.7(
(ga+ga)/(Ra-aa) (3,0...
...(2) must be satisfied.

In addition, the tp of the present invention! The f-characters are listed in the implementation column.

(Implementation row) FIG. 1 is a schematic diagram of an optical system of one implementation row of the present invention. In the figure, 1 is a photographic lens, 2 is an exit pupil of the photographic lens 1, 3 is a planned fine image plane of the photographic lens 1, 4 is a field lens, and 5 is a prism body, which are arranged so that their wedge angles are opposite to each other. It consists of a prism. 6 is a field mask having two apertures, and 7 is a re-imaging lens consisting of two lenses, a first lens Lt and an i2 lens L2. 8 is a light receiving means with two light receiving element arrays such as COD 8-1.8
-2t- has.

In this implementation row i, the field, drain lens 4, p pupil of the reimaging lens 7, and exit pupil 2 of the photographing lens 1 are configured to have a substantially conjugate relationship, and the prism body 5 and the field mask 6 are used. The exit pupil 2 is divided into two areas 2-1 and 2-2. The light flux from the object that has been photographed/transmitted forms a primary object image near the planned image plane 3. Form.

Of the WX primary object image, the light flux S1 that has passed through one of the exits @2 of the photographing lens l passes through the field lens 4 and one of the prisms of the prism body 5, and then is reflected by the re-imaging lens 7 to the light receiving means 8. One light-receiving element row s-i metaphysical surface @
A secondary object image is formed.

Similarly, among the primary object images, the light flux S2 that has passed through the other ll]l 2-2 of the exit pupil 2 of the photographing lens 10 forms a secondary object image on the surface of the light receiving element array 8-2.

Two secondary objects i&! on the light receiving means 8! is photographic lens 1
Depending on the in-focus state, that is, the amount of defocus, the amount of displacement in the light-receiving element array 8-1, 8-2 direction will change. Focus detection is performed by detecting the relative positional relationship between the two secondary object images using the light receiving means 8.

For this reason, the focus detection accuracy is greatly influenced by the imaging performance on the plane of the light receiving element array of the two secondary objects.

In this embodiment, by setting the lens shape of the reimaging lens 7 as described above, spherical aberration, comatic aberration, etc. can be favorably corrected, and a high imaging power lk can be obtained.

Conditional expressions (1! and +21 are related to the lens shapes of the first and second lenses, respectively.

If the upper limit of conditional expression (1) is exceeded and the first lens surface becomes strongly convex toward the photographing lens side, spherical aberration will be insufficiently corrected and comatic aberration will occur. Furthermore, when the lower limit value of conditional expression (11) is exceeded and the second lens surface becomes shaped with a strongly convex surface facing the light receiving means side, the spherical aberration becomes insufficiently corrected.

If the upper limit of conditional expression 21 is exceeded and the third lens surface becomes shaped with a strongly convex surface facing the photographing lens side, the spherical aberration will be insufficiently corrected, and if the lower limit value is exceeded, the third lens surface becomes shaped with a strongly convex surface facing the light receiving means side. In this case, spherical aberration becomes insufficiently corrected and downward coma aberration occurs, which is not preferable.

In this example, the iS@z lens may be constructed of a laminated lens, which allows for good correction of chromatic aberration. By applying this, higher imaging performance can be obtained.

In this implementation row, two o%1B are used without using the prism body 5.
These re-imaging lenses may be arranged symmetrically with respect to the optical axis S by using the lens.

Next, a numerical implementation sequence of the reimaging lens according to the present invention will be shown. In the numerical implementation sequence, the former is the radius of curvature of the i-th lens surface from the taking lens side, and Di is the curvature radius of the i-th lens surface from the taking lens side.
The thickness of the ith lens, the air gap, Ni and the amount of ν are the refractive index and Abbe number of the glass of the ith lens, respectively, in order from the photographing lens side.

Numerical implementation sequence l R1--DI-IJ Nl"L4'J171 yl
=57.4R2-4294D2-0.2 R3-3h294 Di-1,2N2-L491
71 C2-57.4■ζ4- (to) a value implementation sequence 2 L1=L93 DI-L2 N1-L49171
yl-57,41ζ2--5.93 02-0.
2R3-L93 Di-1, 2N2-L49171
C2-57.41ζ4-a93 Number 1 shift implementation 11113 R1 4.04 111-L2 N1-L4917
1 νl-57,4R2--1R1)<0.002-
α2 R3-1αODi-L2 N2-L49171
C2-57.4R4--4,04 Several ft['il! Array 4 R1=, -4435Di-1,2N1-1.49171
C1-57.482-43 D2-α2 R3= 13 03-1.2 N2-
1.49171 v2-57.4fL4- L4
35 Numerical implementation Vill The focal length f and imaging magnification β of the re-imaging lens in l-4 are both j'-14, β--R
1) <0.4.

(Effects of the Invention) According to the present invention, by configuring the re-imaging lens with two lenses having a predetermined shape, the lens system can be simplified, and
Moreover, it is possible to obtain a secondary object height with high imaging performance, and to achieve an image shift type focus detection device that is capable of highly accurate focus detection.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, and FIGS. 2 to 5 are aberration diagrams of numerical implementations 1 to 4 of the re-imaging lens according to the present invention. In the figure, 1 is a photographic lens, 2 is an exit pupil, 3 is a planned imaging plane, 4 is a field lens, 5 is a prism body, 6 is a field mask, and 7 is f4M! IJ lens 8 is a light receiving means.

Claims (1)

[Claims] (1) A re-imaging system that divides the pupil of the photographic lens into a plurality of regions and forms a plurality of secondary object images from the light flux passing through the divided pupil regions is provided on the image plane side of the photographic lens. and arranging a light receiving means consisting of a plurality of light receiving element arrays near the image plane of the reimaging system, and detecting the relative positional relationship of the plurality of secondary object images by the light receiving means. In a focus detection device for detecting a focal position of a photographic lens, the re-imaging system includes a re-imaging lens consisting of a first lens having a positive refractive power and a second lens having a positive refractive power in order from the photographing lens side. When the radius of curvature of the i-th lens surface of the re-imaging lens is Ri, -3<(R2+R1)/(R2-R1)<0.7-0.
A focus detection device characterized by satisfying the following condition: 7<(R4+R3)/(R4-R3)<:3.0.