Long-persistent Phosphor Research Articles

Pseudo-Random Dot Scan Television Systems

The principal psychophysical requirements of the human eye are satisfied by a television frame frequency of about 1 or 2 c/s. To avoid flicker with such low-frame rates, a random dot scan is employed in conjunction with long-persistence phosphors. Experiments show that 15 per cent dot flicker is tolerable. Ten systems are discussed, including a two-million-element picture with 4-Mc/s bandwidth; tape recording at 15 in/s; continuous relaying of satellite pictures; short-wave transmission; phonevision; and very low-frame rate applications that use a scan conversion tube.

High-Contrast Electronic Image-Orthicon Techniques Applied to the Lunar Surface.

The current interest in the structure and mapping of the lunar surface has led to the increased use of various methods of investigating the lunar surface, e.g., photographic stereoscopy over the entire range of lunar libration and the sequential photometry of lunar shadows, as presently employed by the Army and Air Force, respectively. The advent of high-contrast image-orthicon techniques appears to offer a valuable and versatile variation of the conventional point-by-point photometry of the lunar surface. By a combination of the subtraction of a constant bac~ground and the subsequent variable expansion of the residual range of brightness, it is possible to emphasize relatively minor differences in contrast, without the loss of gray-scaling, nearly simultaneously over the entire lunar surface. The effects of the inevitable increase in noise attendant in this technique can be effectively minimized by the use of long-persistence phosphors on the viewing screen and the use of relatively long exposures with the recording camera. The application of these techniques is at present a part of the image conversion program at the Dearborn Ubservatory. They are particularly adaptable to the detection of minor differences in lunar albedo and are capable of delineating fine differences particularly in the lunar maria, especially at full lunar phase, when lac~ of shadows limits the effectiveness of conventional photography. The method, therefore, offers more promise in the detection of differences in texture, and by inference, composition, of the lunar surface rather than in contour determination. Movies illustrating a run across the full moon at constant contrast, the effects of variation of contrast discrimination near the subsolar point, and preliminary studies of relative photometry of line elements using the video signal itself, have been made.