Exposure meter "OPTEK" (OPTIC Expometer) was originally produced at the Leningrad Optical and Mechanical Plant.
Subsequently, it was also produced at other optical production facilities (see logos in the center of the device). The exposure was determined by eye by comparing the brightness of the objects being photographed with a transparent exposure meter scale (stepped optical wedge), some parts of which have unequal density.
"The OPTEK exposure meter is a small box with two rectangular holes. One of them is permanently covered with frosted glass. The second hole is equipped with an opening lid, under which you can see an inclined mirror placed inside the box. Inside the device, between the frosted glass and the mirror, there is a scale for determining the brightness objects (stepped optical wedge) It is a series of transparent numbers (2 - 2.8 - 4 - 5.6 - 8 - 11 - 16). The scale is evenly illuminated through the frosted glass by light that is reflected from objects placed in front of the exposure meter. Each next digit of the scale has a greater optical density, i.e., it transmits a smaller fraction of the light falling on it; therefore, the brightness of the numbers that can be seen when the white cover is folded down gradually decreases from left to right. If objects of low brightness are located in front of the frosted glass, then only the first, most transparent numbers can be distinguished on the scale; the greater the brightness of the objects, the greater the number of digits that can be distinguished on the scale. The top side of the box serves as a calculation device (calculator). It has a movable disk with designations of shutter speeds in seconds and film sensitivity in units of GOST. "[35] The device is designed for shutter speeds from 1/1000 to 15 seconds for films with a sensitivity of 11 to 180 GOST units.