A Low-Background Image Tube for Direct Electronography.
W. A. Hiltner, Wilfrid F. Niklas · The Astronomical Journal · 1961
The use of image tubes for direct electronography at Yerkes Observatory has been frustrated because of intense background resulting from field emission. However, during the past six months, a decrease in background of 10~ has been achieved. This large factor has resulted in a tube that has a background 3 X 102 less than the sky background at the focus of the f/20 40-inch refractor. Furthermore, no ion spot has been detected. The lifetime of the photocathode appears to be unlimited. No change in sensitivity was detected over a period of one month even though the tube was cycled (emulsions inserted and removed) over 200 times. The resolution is 40 line pairs per mm.