Optical test bench with photoelectric optimal focussing - determines focal plane of test piece using vibrating lens system

摘要

The focal plane of a test piece can be determined without recourse to subjectivity assessment of focussed images. A light source (19) projects a beam of light through a pair of lenses (20) and a test plate (3) carrying a test pattern, normally of radial spokes. The light passes through an electromagnetically vibrated intermediate lens pair (13). The test piece lens array is carried on adjustable rails. (10). Another lens (5) and a half silvered mirror (8) focus the image of the test plate on to a concave mirror (6). This reflects the image back through the system to the first lens array (20). in which it is partly deflected by a semitransparent mirror on to a photodiode (22). A signal is produced which depends on the vibration of the intermediate lens pair (13) and on the position of the test piece (2) which can then be altered until the maximum reading is obtained and this corresponds to the focussed position of the test piece.