GB1051968A - - Google Patents

Abstract

1,051,968. Interferometers. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 9, 1965 [March 10, 1964], No.9870/65. Heading G2J. [Also in Division G1] A method of detecting comatic aberration of a light transmissive or light reflective device or medium includes dividing a light beam from an illuminated object into two separate beams, the light beam or both said separate beams being transmitted or reflected by said device or medium, rotating at least one of the separate beams after it has passed from said device, subsequently merging the two separate beams to form two superimposed images of the object, and observing or sensing the interference pattern at least when the separate beams are rotated through 180 degrees relative to each other, which particular interference pattern indicates the comatic aberration of the device or medium. The apparatus shown in Fig. 1 comprises a monochromatic light source 10, an apertured mask 11, a collimating lens 12, a beam splitter 14, three mirrors 15, 18, 19, two beam rotating devices 16, 17 and a screen 20. A lens 13 which is to be tested is placed in the collimated beam passing from the lens 12. The beam splitter 14 divides the beam passing from the lens 13 into two beams 22, 23 which are rotated in opposite senses through 90 degrees by the devices 16, 17 respectively. When the two beams are recombined by the semi-reflective mirror 19 they have thus been rotated through 180 degrees relative to each other. The screen 20 upon which the two images are projected may be replaced by a photo-electric cell and detector means, the device 16 being continuously rotated by a motor. A phase retarding plate 25 may be placed in the path of the separate beam 23 in order to amplify the variations produced on the screen 20. In a further embodiments Fig. 4, (not shown) the two separate beam are arranged to pass through the lens under test.