To determine the field of view of existing lens. Select the correct camera format scale, then rotate the View Finder barrel unit the dot coincides with the lens focal length. The object viewed through the finder is the same as seen by the camera. Example : In the case when the camera format is 2/3 type and the focal Iength of the Iens is 12.5mm, adjust the barrel as shown. To determine what focaI length lens to use. 

First, look the object through the finder's windows, then turn the barrel to find the desired field of view. Next, using the correct camera format scaIe, read the lens focal length which coinciders with the dot on the barreI.