An Improved Optical System for Cathode-Ray Recording

Abstract

Recent years have brought the cathode-ray tube into considerable prominence as an instrument for registering and recording electrophysiological phenomena. With the recent advances in high-mu amplifier tubes, the most infinitesimal biological currents come within the scope of cathode-ray study. This has created a need for a reliable and highly efficient optical system for recording on photographic paper. A number of expedients have already been suggested and used, among them those of Gasser and Erlanger, 1 Rijlant, 2 and McCulloch and Wendt. 3

The methods fall into 2 main divisions: (1) still photography or contact prints of single waves or periodically recurrent phenomena, obtained by photographing a standing wave or the persistent afterimage of a single excursion with a still camera, or by holding photosensitive paper in direct contact with the tube screen while the fluorescent dot executes a single excursion across the screen; and (2) photography on paper moving in one axis, of excursions of the dot in a perpendicular axis, this being the method of necessity in the study of continually changing wave forms.

For quite some time the fluorescent screens incorporated in cathode-ray tubes had such low actinic rating and such long persistence of the after-image, that registration was limited to the first type of recording, namely, still photography. However, with the improvement of highly actinic and extremely low persistence screens such as the R.C.A. phosphor types 2 and 5, recording on moving bromide paper or film has become a general practice. The various methods in vogue employ a spherical lens to project an exact image of the dark screen and the bright moving dot upon the moving paper. When a round spot of light is so used in recording, the resulting record can in no way compare with the sharp, clean-cut record of hairline recording.