SU415536A1 - - Google Patents

Description

one

The invention relates to devices for automatically controlling the image quality of optical systems, in particular photographic lenses.

There are known devices for controlling the quality of a lens, containing a test object in the form of a slit, illuminated by a light source, an auxiliary lens, a raster with discretely varying frequency gratings, the spatial frequency of one of which is close to zero and used for normalization, a photodetector, amplifiers and electrical filters to extract the signals corresponding to the selected spatial frequencies, and the registration system, by which the quality of the image transmission of the objects is judged by the ratio of the values of these signals tivom.

A disadvantage of the known devices is the absence of an automatic focusing, which leads to a lengthening of the measurement process and allows the appearance of subjective operator errors during manual focusing.

In the proposed device, to reduce the time and increase the accuracy of control, the three-dimensional raster gratings are placed on mismatched tracks, and the outputs of the normalizing and other selected frequency filters through the detectors and the adder are connected to the input of the phase-sensitive circuit that controls the axial movement of the controlled lens to which another input is connected a reference voltage generator associated with an oscillating axial displacement drive of the auxiliary lens.

FIG. 1 is a schematic diagram of the device described; in fig. 2 - raster section; in fig. 3 - dependence of signals and on defocusing / for two spatial frequencies.

The device contains a test lens 1 and a slit diaphragm 2, illuminated by light from a source 3 through a condenser 4 and

frosted glass 5 and located at the focus of the collimator 6. Mirror 7 serves to break the optical axis and to create off-axis beams. An image of the slit is constructed in the focal plane of the test lens and

The lens 8 is projected onto a glass disk 9 with raster lattices applied to it. The disk is driven into rotation at a constant speed by the engine 10. The strokes of the raster grid are located on mismatched tracks (Fig. 2). A lattice 11 with a spatial frequency close to zero is intended to normalize the signal, since the contrast transfer ratio for such a frequency does not depend on the quality of the lens under test.

The grids 12 and 13 have two other predetermined spatial frequencies. The image of slit 14 overlaps all three grids at the same time, and the flow past Sbetov.0.i falls on the photodetector 15 located behind the raster (Fig. 1). The amplitudes of the first harmonic of the electrical signals at the output of the photodetector are proportional to the coefficients of irregular contrast for the spatial frequencies of the gratings 11-13.

From the photo-receiver output, the signal enters the broadband amplifier 16 and further to the selective amplifiers 17-19, whose resonant frequencies correspond to the frequencies of the gratings 11–13. Pass through the detectors 20-22, these signals fall on a comparison circuit consisting of potentiometers 23, 24 and comparators 25, 26. Potentiometers serve to set the threshold values of the signals below which the corresponding comparators are triggered, and the signal "scrap through the logic circuit" I / ILR1 27 is fed to the display in latch 28.

The auxiliary lens 8 mounted on the tuning fork generator 29 performs in-depth scanning of the image of H1, spruce, and thereby modulates the output signals with a natural frequency.

The voltages from the outputs of the amplifiers 17, 18 are detected by the detectors 30, 31, added to the adder 32, amplified by a selective amplifier 33 tuned to the frequency of the tuning fork 29, and fed to the input of the phase detector 34.

The reference voltage to the phase detector comes from the excitation winding 35 of the tuning fork generator.

From the output of the phase detector, a signal in the form of a constant voltage proportional to the deviation from the plane of maximum contrast and the polarity of which corresponds to the direction of deflection is fed to the modulator 36, amplifier 37 and affects the motor 38, which through the gearbox 39 drives the lens in the plane of maximum contrast . . - Auto; automatic focusing is done

, - the sum of the signals t / o K.Ui (Fig. 3) taken from 5 outputs of amplifiers 17, 18 and corresponding to the two spatial frequencies of the gratings 11 and 12. The signal Lo ensures sufficiently large range and reliability of the focusing system, and the signal is the focusing accuracy according to the maximum of the contrast corresponding to the spatial frequency chosen in advance, which is optimal for a given region of spatial frequencies.

The tuning fork generator is

 a mechanical oscillatory system, encompassed by the value of feedback, consisting of an adander 40, an amplifier 41 and an exciter 36. At the end of the focusing process, the tuning fork generator is turned off by shorting the exciter winding by contact 42.

Subject invention

5 A device for quality control of a lens, containing a test object with an illuminator, an auxiliary lens, a raster with discretely varying frequency by dashed renlets, one of which is normalizing, a photo receiver, included in an amplifying circuit with narrow-band filters and a recording system, characterized in that , in order to reduce the time and the accuracy of the control, raster dashes

5 are placed on mismatched tracks, and the outputs of the normalizing and other selected frequency filters through the detectors and the adder are connected to the input of the phase-sensitive circuit that controls the axial non-placement mechanism of the monitored lens, which is connected to the other input of the reference voltage generator connected to the oscillating axial drive moving the auxiliary lens. O p

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