Optical image-oriented focusing appts. for projector

摘要

The object in a plane (2) at right angles to the optical axis (A-A) is imaged in a parallel plane (12) by an objective lens (4) adjusted (s) by a drive (6) under electronic control (10) responsive to a photodiode (16) which receives the reflection from a small mirror (8) rotatable about its own axis of symmetry. The pref. circular mirror is positioned close to the entry pupil of the objective lens, with the object plane ad the photodetector equidistant (aD = as) from its centre.