JPS6315208A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To contrive miniaturization and light weight of the titled device by effectively utilizing a part between an interlocking lens of a slave lens system and an image forming surface, executing a pupil division before forming an image, forming two images on a one-dimensional image sensor, and deciding a focused state of an AF optical system from its relative position shift. CONSTITUTION:In case of a state being out-of-focus from an object, an image of the object is formed in a position which has been shifted by DELTAx from an image forming position of an AF first lens system 5 at the focused time. In this case, an image on a one-dimensional image sensor 8, which is formed by an AF third lens system 7 for dividing a luminous flux which has passed through an AF second lens system 6, into two so as to be symmetrical to an optical axis is shifted up and down by DELTAy from an optical axis of the AF third lens system. Therefore, an inter-image distance which has been formed on the one- dimensional image sensor is detected by the one-dimensional image sensor 8, and a focus adjusting lens of an image pickup optical system is brought to a driving control by a driving device such as a motor, etc., so as to become DELTAy=0, by which automatic focusing is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a focusing device in a camera, and more particularly to an automatic focusing device having a slave lens linked to a focus FJII focusing lens of a photographing lens.

(Prior art) Conventional - As an automatic focusing device for an eye reflex camera, it is an automatic focusing device that has a slave lens linked to the focus adjustment lens of the photographing lens, and the exit pupil of the optical system is divided into two, and each It is known that the amount of defocus is detected from the amount of relative positional deviation in the direction orthogonal to the optical axis direction of the image formed by the image forming apparatus. I can give you the publication number.

As shown in FIG. 4, the former has a microlens array near the imaging plane of the slave lens 5 that works with the focus adjustment lens 1 in the imaging optical system, and a microlens array behind each microlens array.

It consists of a detection element 9 with a pair of light-receiving elements arranged so as to detect the exit pupil divided into two parts almost symmetrically across the optical axis at a position almost conjugate with the exit pupil of the photographic lens. This method detects the image formed by each pupil, and the latter method detects the image formed by each pupil, as shown in FIG. A pair of re-imaging lenses 10 are arranged so as to divide the exit pupil into two, the image formed by the re-imaging lenses is detected by a one-dimensional image sensor 11, and the photographic lens 1.2 is focused. The defocus is detected based on the distance between the images, based on the distance between the pair of images.

In both of the above two conventional methods, a movable quick return mirror or the like is arranged between the photographing lens and the image forming surface, like an eye reflex camera, and an optical system for focus detection is formed after the image forming surface. It was invented under the constraint that the lens system must be linked to the focus adjustment lens of a photographing optical system of a still camera, video camera, etc. This requires wide spacing between the detection elements, which poses a major disadvantage in reducing the size and weight.

(Problems to be Solved by the Invention) This invention requires a quick return mirror or the like between the lens and the defocus detection element. ! In a slave lens type automatic focusing device that does not require space for a structure, the slave lens optical system is intended to be smaller and lighter than that of a conventional type.

Structure of the Invention (Means for Solving the Problems) This invention provides a method for converting a convergent light beam that has passed through an interlocking lens in an autofocus lens that moves in the optical axis direction in conjunction with a focus adjustment lens of an imaging lens system into the interlocking lens. An optical system fixedly placed at the rear makes it almost afocal, and the afocal light beam is passed through a pair of apertures arranged symmetrically on the optical axis.
The optical system is assembled to form a pair of substantially equivalent subject images on the dimensional image sensor, and the focus of the imaging lens system is adjusted so as to eliminate the deviation of the image from the focused image position on the image sensor. This purpose is achieved by controlling and moving the adjustment lens in the direction of the optical axis.

(Function) The focus detection method using the automatic focusing device of the present invention will be explained below. Figure 2 is for explaining the principle.
The focus detection optical system includes an automatic focusing (AF) lens system 5. which works in conjunction with the focus adjustment lens of the photographing optical system from the subject side. The AF second lens system 6 makes the image formed by the lens system 5 more afocal when the subject is in focus, and the light flux passing through the AF second lens system 6 is divided into two parts symmetrically on the optical axis. On the one-dimensional image sensor, approximately equivalent 2
A pair of AF third lens systems that form two images7. and AP
The lens system is composed of a one-dimensional image sensor 8 placed near the focal point of the third lens system. FIG. 2(a) shows a state where the subject is in focus, and the subject image by the AF second lens system 5 is formed on the object side focal point of the AF second lens system 6, and the subject image is formed by the AF second lens system 6. projected to infinity,
Furthermore, a pair of substantially equivalent subject images are finally formed on the one-dimensional image sensor 8 by the pair of AF third lens systems 7, separated by the distance 1 between the optical axes of the AF third lens systems.

Figure 2 (b) shows the state where the subject is out of focus 1
A subject image is formed at a position shifted by ΔX in the optical axis direction from the imaging position of the AF lens system 5 at the time of focusing, and at this time A
AF third lens system 7 for subject image by F second lens system 6
The distance T from T is given by the following equation, where d2 is the distance between the principal points of the AF second lens system and the AF third lens system.

T=f2X(--knee-1)+d2 (1)Δ
X At this time, the image on the one-dimensional image sensor 8 formed by the AF third lens system 7 is AF? This results in a vertical shift of Δy from the optical axis of the third lens system.

If the distance between the optical axes of the pair of AF third lens systems 7 is 1, then Δ
y is given by the following equation.

Δy=d〒x f, (2) However, here, the focal length of the AF 1st, 2nd and 3rd lens system is f, f2, f
, said. Therefore, the distance between the two images on the one-dimensional image sensor changes from 1 at the time of one focus to 1+2Δy, corresponding to the focal shift ΔX of the AF lens system, and 1f2/ΔXI
In the range of >>1, the signs of ΔX and Δy correspond, and -
The distance between the images formed on the dimensional image sensor is detected by the -dimensional image sensor 8, and the focus adjustment lens of the imaging optical system is driven and controlled by a driving device such as a motor so that Δy=o. Charging is done.

(Embodiment) FIG. 1 shows an embodiment of an automatic focusing device, and the structure and operation of the present invention will be specifically explained with respect to the embodiment, including the detection logic of 2Δy.

In the embodiment shown in FIG. 1, the subject image signal g T + 1 (i= 1 +
2 +...N; where i corresponds to the element position on the one-dimensional image sensor. ) is converted into a digital value by an A/D converter and read into a microcomputer.

Assuming that the element pitch of the one-dimensional image sensor is P, and each image signal is composed of n pieces, the image signals below the optical axis in Fig. 2 are gazes), gazes), ... g
(n's), and the upper image signal is g(.+1 or 5).

g+c+z+s+,...g,. +n+s). However, it is assumed that C is divisible by l/p. Further, S corresponds to the image shift that can occur at the maximum focus shift. [-11
'-, the above image signal is replaced by the following.

a(++”g(i+ i=1+s, 2+s,...
, n+5b(s +”g+ I 1 j=c+14s
, c+2+s, -c+n”s (3) Above a,
The following calculation is performed on the b signal.

The above calculation is performed as j=-s, -s+1 .corresponding to the number of elements S corresponding to the maximum image shift that can occur. . . , 25+1 of S is performed, and the results are plotted in a coordinate system with the vertical axis being V(J)*the horizontal axis being j, as shown in FIG. 3, and the intersection with the V=O axis is determined. If there are multiple intersections, find k where V(k+x)V(K) is maximum and interpolate between k and +1 to obtain the desired lateral shift @2Δy. That is, 2△y=−pX (k◆■k)V. K 1
-V(K.t) (5) The above is JP-A-57-
This is an example in which the calculation method described in Publication No. 45510 is applied.

Next, a method of configuring the slave lens system will be explained.

First, the detection accuracy e of the distance between two images on the -dimensional image sensor corresponds to a constant value α The various constants of the slave lens system, that is,
Focal length fi, f2, f of each lens system of the AF optical system
4. Second. Third lens system distance fid2. Set the distance between optical axes 1.

Next, the maximum image shift: l is made so that the distance between the two images on the one-dimensional image sensor is larger than the shift Δy□8 from the reference position, which corresponds to the maximum focus shift that occurs in the photographing optical system.
s is set, and it is determined whether the two image signal detection units 2n and the maximum image shift amount 2S can fit within the range of the length of the one-dimensional image sensor to be used, including the distance 1 between optical axes. In addition to the above conditions, the focal length of each lens group of the slave lens system and whether the required aperture can be achieved are determined by the fact that the equivalent F value of the imaging system to the -dimensional image sensor determines the subject light amount detection sensitivity of the AF system. The decision will be made taking into account whether or not the amount is sufficient for maintenance.

The maximum focal length of the photographing optical system is fT, the focal length of the focus adjustment lens is fF, and the closest photographing distance is Um. Equal values are chosen. The detection accuracy of the image interval is determined by the detection logic used, variations in sensitivity of the -dimensional image sensor, errors during A/D conversion, external noise, etc., and can be expressed as the interpolation accuracy of equation (5) using the logic described above. , e is given by the following equation.

e = p / m Therefore, if the value obtained by converting e to the focal deviation of the imaging plane is Δε, then ΔE = αXE (α≦1) (6) The relationship between e and the amount of focal position deviation ΔXe of the AF lens corresponding to e is (
1) Approximating 1Δx / f z I << 1 in equation (2), ΔXe is equivalent to the amount of defocus of the focus adjustment lens of the photographing optical system, and converting this to the defocus of the captured image is given by the following formula. It will be done.

Therefore, 1. f2,f, is selected.

Furthermore, the maximum image shift amount S is determined by the fact that the maximum focus shift scene ΔXTm of the photographing optical system is given by the following equation (10), and (9)
From the correspondence with Eq.

Δ XTII Medium f D2/U1. l
(10) However, equation 11) is obtained on the assumption that e:czi-i=2Δy+++ax:ΔXrm approximately holds true.

Furthermore, the total length of the -dimensional image sensor is (9) (1
1) For each 1°S determined to satisfy equation 1 and the number n of elements used for image comparison calculations, the element pitch is determined as follows, with p being the element pitch.

pn+2ps+L≦L (12) For example, using a one-dimensional image sensor with 128 elements and a pitch of 30 μm, the focal length f=8.5 to 51 mm (
fr=51m) Focal length of focus adjustment lens fF=
38nn, g=0.05mm, Uvm=1000
Considering wa's AF optical system.

f 1 = f r = 38 va (4) The image shift precision within one element that can be interpolated by equations (5) is e=p/40, and the configuration is such that E approximately corresponds to 2e.

The maximum defocus amount ΔXTII of the imaging system is given by the following equation.

ΔS T11==2.601s Therefore, the required maximum element shift amount S should satisfy the following.

Set S=3. Suppose that 20 elements are selected as n.

1 <30X 128-20X30-3x30=315
0 (tt m) Therefore, choose l=3m.

In order to make ε correspond to 28, convert E to the focus shift ε' of the AF lens, and use equation (8) to calculate 1. f2,
All you have to do is find the relationship between f.

from f%≦55.5f.

If f, = 5 ytn, 1f21≦16.6
mm, and select f,=-15IIn. Also AF 2nd
The distance d2 between the lens and the third lens is a = 2.5 mm.
Select.

The above can be summarized as follows.

Example fl dl 1st lens 38mm 23i* 2nd lens 15 m 2 , 5 m 3rd lens 5 na 3 m Lens total length
23+2.5+5=30.5m As described in detail, according to the present invention, the space between the interlocking lens of the slave lens system and the imaging plane is effectively utilized to divide the pupil before forming an image, so that the image can be displayed on a one-dimensional image sensor. Since two images are formed and the in-focus state of the AF optical system is determined from the relative positional deviation between the two images, an automatic focusing device can be constructed that is smaller and lighter than conventional systems.

Note that as the AF first, second, and third lenses described here, not only a normal refractive optical system but also a reflective system with a lens function, a plastic lens, a gradient index lens, etc. can be used, and they can be used to correct aberrations. Therefore, it goes without saying that it may be composed of an aspherical lens or a plurality of lenses. Further, the pair of third lenses can be easily assembled if configured as a pair of plastic lenses or gradient index lenses.

7. Brief explanation of the drawings Fig. 1 is a block diagram showing one embodiment of the present invention, Figs. 2 and 3 are diagrams explaining its operation, and Figs. 4 and 5 are block diagrams of conventional examples, respectively. show. The numbers written in the figure indicate the following.

1: Focus adjustment lens section of the imaging optical system 2: Zoom lens section of the imaging optical system 3: Low-pass filter section 4: Image sensor section 5: AF lens system linked to the focus adjustment lens 6: AF second lens system 7 : Pair of AF third lens system 8 and one-dimensional image sensor 9: @ Split detection element 10: Pupil division re-imaging optical system 11: Detection element Patent applicant Konishi Roku Photo Industry Co., Ltd. Applicant's agent Patent attorney Kuruma Sahara Power (2 others) Army Figure 3 Figure 4

Claims (1)

[Claims] 1) A pair of optical systems installed symmetrically on the optical axis after the convergent light beam transmitted through the lens system that moves with the focus adjustment operation is made into an almost afocal light beam by the following optical system. A pair of substantially equivalent subject images are formed on the focal position detecting means, and when the distance between the images and the focus of the photographing optical system are at their optimum, the focal position is determined. An automatic focusing device characterized in that it is configured to control driving of a focus adjustment lens based on the amount of deviation between a pair of images formed on a detection means. 2) The automatic focusing device according to claim 1, wherein the lens system is a slave lens system provided near a focus adjustment lens of a photographing optical system.