Automatic focus correcting system for submarine periscope - uses photocell to discriminate between images in front or behind its plane to control focus lens displacement motor

摘要

The observation head of a periscope is connected by a long tube to a box containing the observation elements. The beam from an area of the field of view is reflected by a prism to pass to a semi transparent mirror where it is split into two paths one of which passes to an eyepiece. The other path is directed to a photographic plate. Automatic focussing correction system comprises a luminous source whose radiation is outside the luminius spectre of the observed field. The beam passes through an objective lens to pass to the semi transparent mirror where it is separated from the light from the field of view. A photocell discriminates between images in front of and behind it and a servo circuit determines the exact image plane from a sight near the source. The output controls a motor to displace the objective lens to maintain the two signals equal in amplitude and thus correctly focus the periscope.