SU1198443A1 - Device for focusing lens - Google Patents

Description

The invention relates to film photographic equipment, more specifically to single-lens mirror cameras with automatic or semi-automatic focusing of the lens.

The aim of the invention is to improve the accuracy of focusing by analyzing changes in the luminous flux p the exit pupil of the optical system.

FIG. 1 shows the optical scheme of the device in the camera with control units; FIG. 2 is a section A-A in FIG. one; in fig. 3 is a block diagram of the device; in fig. 4 and 5 are the signal change curves in the proposed device on two annular groups of photodetectors and, accordingly, the difference signal change curve; in Fig.6, the curve of the change in illumination on the photodetectors during defocusing is shown if the object is "half-plane" '(one object boundary is the background).

The optical scheme of the focusing device (Fig. 1) consists of a focused lens 1, a sighting mirror 2, made in the central part translucent, a collective 3, pentaprism 4, an eyepiece 5 (positions 2-5 is a sighting device), an additional mirror 6, directing light through the beam-splitting prism, consisting of prisms 7 and 8, into two groups of light-receivers 9 and 10, in front of which short-focus lenses 11 and 12 are installed, and extended diaphragm devices 13 and 14. Photo-detectors 9 and GO are installed near the exit pupils in two branches eskopicheskoy system. In this case, the points of the front focus G _p , G ₍₂ ^lenses 1 1 and 12 are located in front of and behind the plane 15, which is associated with the frame window of the camera 16. The different position of the points

and K, _{2 is} obtained as a result of the fact that the stroke length in glass in prisms 7 and 8 is different (the output face of the prism 8 is farther from the beam-splitting surface than the exit is, the maximum face of prism 1), and the focal lengths of lenses 11 and 12 are the same. The distances of the points Г „and Г, _г from the plane 15 are chosen equal by the order of several tenths of a millimeter and can be more than 1 mm. Diaphragms 13 and 14 have holes parallel to the optical axis, the number of which can be from 4 or more (for example, 6 holes as shown in Fig. 2 on an enlarged scale).

Each of the holes of the diaphragms 13 and 14 are separate light-sensitive areas площадки groups of photodetectors 9 and 10). The first and second groups of photodetectors 9 and 10 can be made in the form of a ring, the center of which lies on the optical axis.

The control circuit consists of blocks 17 and 18, in which absolute values of the differences of signals from neighboring photodetectors are formed (all the differences of signals from the photoreceivers of group 10 are determined in block 17, and in block 18, all differences of signals from the photoreceivers of group 9 are determined). Then all the differences from block 17 are added up in the adder 19 and all the differences from block 18 are added up in the adder 20. From the outputs of the adders 19 and 20, the signal is sent to block 21, in which the difference between the signals from the adders 19 and 20 is determined. depends on whether the image is in front of or behind the plane 15.

Depending on the sign of this difference, one or the other turns on, the LED indicator 22, which indicates the direction of rotation of the lens 1.

At the moment of precise focusing, the differential signal in block 21 is minimal and then on the indicator 22 the middle LED turns on, which can be made of a different color than the LEDs indicating the direction of defocusing. The described scheme allows semi-automatic focusing - with the movement of the lens 1 is carried out manually.

I

For automatic focusing of the lens 1, a block 23 is inserted into the control circuit, comprising an electric motor, an electronic circuit and a drive (not shown) connecting the electric motor with the lens 1.

Structural electronic circuit blocks 9, 10, 17-22 for. Semi-automatic can be performed as follows. The first group of GO photodetectors (for example,

6 elements) consists of six photodetectors - a 24-diode photodiode

operational amplifier; second corpse "

PA photodetectors 9 is similar - with. 1198443

3

It consists of photodetectors 5. Neighboring photoreceivers 24 are connected to the inputs of comparators 26 (6 pcs.), and photoreceivers 25 are connected with similar comparators 27 (also 6 pcs.), in which the absolute differences of signals from neighboring photodetectors are determined. ' The outputs of all the comparators 26 of the first group are connected to the adder 28, and the outputs of the second group 27 - with the same sum-’’ 29. The operational amplifier 30 (subtraction unit) contains the difference between the signals from the adders 28 and 29 of the first and second groups. The block 30 is connected to the decision block 31 (blocks 30'and 31 correspond to block 21 in Fig. 1), which controls the three LEDs of the indicator 22. The middle LED of the indicator 22 turns on at the moment of precise focusing, and all the LEDs of the indicator-22 are observed in the field of view 3-5

. In the photodetector device, they are located near the exit pupil of the optical system, due to which the total signal in the position when the image is in the front focal plane of one of the short-focus lenses becomes minimal, since the contrast in this plane is minimal. When the image is projected in a position in front of or behind the front focus of the lens of lenses 11 or 12 (Fig. 1), the contrast in the exit pupil increases and the signal from the groups of photographic receivers 9 and 10 increases (Fig. 4), · Thus, focusing curves signal Y have a minimum, and in the rest of the focus area this signal is always greater than the predetermined and threshold 'and therefore the defocusing sign can always be defined (Fig. 5) in the entire defocus area of lens 1

four

(from oo to the initial value of the distance Zn) · In this case, the regions a, c expand, and the region b becomes smaller (Fig. 4 and 5). Angle ού on the cree—

5 won V, = λ ^ (φ) increases, which allows to obtain a higher focusing accuracy. The sign of the signal is always easy to determine, since the V curve always lies above the pore.

¹⁰ ha or below. Differential sig ·

1 cash is obtained by a significant amount even for the “one border” object. '

FIG. 6 shows the distribution of illumination in the annular zone of the exit pupil ’depending on the angle ό in the plane perpendicular to the optical axis of this system, if the object is a“ one border ”, with

20 different defocusings a, b, c. The curve a corresponds to the case of light, a photodetector, when the image of the border is in the front focus short-

25 of the focus lens or P ₁₂ (FIG. 1). The proposed focusing device provides work with all interchangeable lenses, while the defocusing sign is determined during pain

30 movements of the main lens. In determining the sign of the defocusing, the difference signal is always higher than the threshold signal, and in the exact focusing zone, the slope of the difference signal curve is large due to the detection of changes in the light flux in

пределах within small areas of the ring (the exit pupil’s primary zone, which gives the maximum change

40 signal and improves focusing accuracy. .

The device can work without. diaphragms 13 and 14 (Fig. 1), which simplifies the design, facilitates the design of the system 45. In this case, the photodetectors are installed near the exit pupil of the telescopic system

1198443

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ΦυΖ 3

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Claims (2)

1. DEVICE FOR FOCUSING THE LENS, containing a sight device with a translucent central zone, an additional mirror, forming a plane associated with with a focusing plane of the lens, a beam-splitting element that forms two optical channels, each of which has a group of photodetectors, the outputs of which are connected to the inputs of comparators connected to a summing device, the output of which is connected to an indicating device, characterized in that analysis of changes in the luminous flux in the exit pupil of the optical system, sequentially installed between each beam-splitting element and each group of photo-photo elements are introduced into each channel Additional short-focus lens and aperture with holes forming the annular zone, each of which is associated with a corresponding photoreceiver, while the focal planes of the additional lenses are located near the plane associated with the focusing plane of the focused lens at an equal distance from it, and successively located photoreceivers of each group are pairwise connected to the inputs of the comparators through the introduced schemes for determining the absolute difference of signals, and the summing device in It is satisfied in the form of two adders, each associated with a respective group of photodetectors, and is connected to a display device inputted through the determination unit defocusing sign. 2. The device according to p. ^ Characterized in that, in order to simplify the design, the photodetectors of each group are installed directly behind the additional lenses in the exit pupil of the optical system. 51) „, 1198443 > one , 198443 2