1. PURPOSE OF THE DEVICE

Optical exposure meter «OPTEK» is intended for measuring exposure times at dayligtht and artificial light conditions for black-white photography.

2. THEORY OF OPERATION

The functioning of the «OPTEK» exposure meter is based on visual estimation of the relative brightness of matte glass, directed towards the scene being photographed. The relative brightness of the matte glass is determined using graded optical wedge, which has a row of transparent numbers on it : 2; 2, 8; 4; 5, 6; 8; 11; 16. The optical density of these numbers evenly increases with the increase of its numeric value, and all the rest of the optical wedge is opaque. With higher relative brightness of the matte glass, more numbers will be distinguished by an eye at the given level of adaptation, up to the last number in a row - 16.

3. DESCRIPTION OF THE CONSTRUCTION

Exposure meter is a plastic box (4, fig. 1), one of smaller sides of which has a window, covered with a matted glass (2). The light reflected from an object being photographed, falls through the matted glass onto the optical wedge and then is reflected by mirror (3) upwards (to the photographer's eye). On the upper side of the box there is a scale with F-values (1) and a rotating scale with exposure times (5). The exposure times scale has three rows of numbers. Three of them corresponds to different light conditions (artificial light, cloudy weather, sunlight or snow); numbers in the fourth row means film sensitivity.

The exposure times scale has values of exposure time in seconds and fractions of second. The whole seconds values are underlined, starting from one second and more.

Near the disc there is a folding cover (6). When the cover is opened, it allows to see the optical wedge scale and covers the mirror from direct sunlight.

4. EXPOSURE TIME SELECTION

When selecting the exposure time the exposure meter should be directed with its matted glass to the object being photographed and its cover should be opened. Looking into the exposure meter determine, in ascending order, from left to right, the last distinguishable number on the optical wedge. Say, this number is 4 (7, fig 1). Then rotate the disc with the exposure values scale until 4 on the scale of diaphragm values aligns with the sector of the disc where the sensitivity of the film in the camera is located 1) (picture shows the sensitivity of 45 GOST). Then for determining of the right exposure value the light conditions should be estimated. In this device three levels of external light are provided for. In case of taking pictures indoors, at low light level, use the exposure scale at the inner ring of the disc, marked «Â ÏÎÌÅÙÅÍÈÈ». High light conditions means taking pictures at sunny weather and light clouds; the needed exposure values for this conditions read on the outer ring of the disc, marked «ßÑÍÀß ÏÎÃÎÄÀ». When taking pictures at cloudy weather, when the whole sky is covered with clouds, or when taking pictures in the shade, determine the exposure using the middle ring of the disc, marked «ÏÀÑÌÓÐÍÀß ÏÎÃÎÄÀ». According to the required photographic conditions select the aperture value of a lens and according to the weather conditions read the needed exposure value at the corresponding ring of the disc, against the selected aperture value.

1) The diaphragm scale is labeled up to 22. In case if number 16 will be clear and bright, use number 22 of the diaphragm scale.

Thus, in the example case (fig. 1) at sunny weather at aperture 4 the exposure time will be 1/50 sec., at aperture 11 - 1/5 sec, at aperture 2,8 - 1/100 sec. etc (assuming film sensitivity of 45).

At other filming conditions use corresponding sequence of exposure times. For example, at aperture 11 the exposure times will be : 1/5 sec. — at sunny weather, 1 sec. — at cloudy weather, 4 sec. — indoors.

In case of photographing of open distant objects at sunlight the exposure, determined using the exposure meter, should be decreased 2 — 4 times. The exposur meter «OPTEK» gives exposure values for films with sensitivity of 180; 90; 45; 22; 11 GOST, which represents almost all range of films, used for photography.

It is necessary to remember that when determining the exposure the disc with exposure values scale should be rotated until alignment of the sector, containing the selected film sensitivity with the corresponding number at the diaphragm scale.

When using the divice it should be taken into account that the result depends on level of adaptation of an eye at the moment of observation, so it is not possible to use the device when the user is located in sufficiently lower ligth condition than that of a subject being photographed, like when photographing a street out of the window, or from under a dark arch.

As it is clear from this description, the «ÎÏÒÝÊ» exposure meter, like most optical exposure meters, requires some experience for use. It is necessary to learn to properly determine the last visible diaphragm number on the wedge scale, to properly estimate light conditions, as well as features of the objects being photographed. Errors made in these estimations could lead to considerable errors in exposure.

Learning to use this device helps to reduce these errors.

In case when the film sensitivity is given in another system, it is possible to use the following table :

GOST 16 22 32 45 65 90 130 180 250
H & D 400 550 800 1100 1600 2200 3200 4500 6500
DIN 14/10 15/10
16/10		 17/10 18/10
19/10		 20/10 21/10
22/10		 23/10 24/10
25/10		 26/10

The ratios between different systems, provided in this table relates to films and plates for general use.

5. HANDLING THE EXPOSURE METER

It is necessary to protect the exposure meter from moisture and dust. The device requires delicate handling and protection from shakes and scratches on the matte glass and mirror.

6. IN THE BOX

In the box should be found:

  1. Optical exposure meter, model «OPTEK».. 1 pc.
  2. Packing box........... 1 pc.
  3. Brief description of the device......... 1 pc.

7. WARRANTY

The organisation guarantees the faultless functioning of the device during one year if it is used according to description and is stored at normal warehouse conditions no more than one year.

Please report imperfections found in the device to the organisation through the seller.

august 1962 QC