Microscope photoélectrique

1,161,917. Photo-electric microscopes. SOC. GENEVOISE D'INSTRUMENTS DE PHYSIQUE. June 16, 1967 [Oct.18, 1966], No.27936/67. Heading G1A. [Also in Divisions G3 and H3] A photo-electric microscope of the type comprising a vibrating member for scanning the field of view is provided with means for deriving a first error signal dependent upon amplitude errors in the vibration and a second error signal dependent upon asymmetry of the vibration about a datum position and means utilizing these signals to correct any amplitude or symmetry errors in the vibration. Rigidly attached to the vibrating member (which may be a shutter, mirror or parallel sided glass block) is an auxiliary mirror 19. Two beams of light produced by a collimating lens 12 and diaphragm 14 are reflected on to a further diaphragm 20 having a slot 21 through which the beams may pass to a photo-cell 22. The separation of the beams is #2/2 times the amplitude of their oscillation across the slot 21 so that when the vibration of the mirror is symmetrical and of the right amplitude, the photo-cell 22 produces equally spaced pulses. The photo-cell pulses are fed to a differentiator and shaper 24 to produce short pulses which repeatedly set and reset a bi-stable circuit 26. Any amplitude error causes a variation from unity in the mark/space ratio of the bi-stable output and this is detected by a low pass filter 27 to give a D.C. amplitude error signal Va. The error signal controls the gain of a circuit 29 supplying current to the vibrating member to keep the vibrational amplitude constant. The pulses from one side only of bi-stable 26 repeatedly set and reset a further bi-stable 31. Any asymmetry in the vibration causes the mark/space ratio of the output of bi-stable 31 to vary from unity and this variation is detected by a low pass filter 32 which produces a D. C. symmetry error signal Vs which is added to the vibration current from circuit 29 to reduce any symmetry error. In modifications, the signal Vs may be combined with the output of circuit 29 before passing through a common power amplifier, Fig. 10 (not shown) and the source of light 11 may be eliminated by taking light from the light source of the photo-electric microscope itself, Fig. 2 (not shown).