The advantage of reducing the aperture of large telescopes for visual observations of the details of the brighter planets is still a debated question. However, during the present season while Mars has been low and atmospheric conditions, rarely steady at Chabot Observatory, have been disturbed by several heat waves, we have found diaphragms a distinct advantage. Members of the Eastbay Astronomical Association, many of whom are skilled amateurs, and the casual visitors all agree that the reduced apertures give the most satisfactory views of the planets under average conditions here. Mr. Alfred Leach, who by trade is a skilled electric arc welder, and also an amateur who has an all-welded telescope1 with which he has done very creditable observing of Mars, proposed, designed, and made a set of diaphragms for the 20-inch refractor at Chabot Observatory at his own expense. His design is so simple and so successful that others may be interested. The 20-inch refractor, now resplendent in a coat of WPA aluminum paint, is shown with the entire assembly, which weighed before attachment to the telescope about twenty-five pounds. Mr. Leach's description follows : "The diaphragms installed by me in September, 1939, on the 20-inch refractor permit the instrument to be used at full aperture or with a 14-inch or 8-inch opening by turning a knob at the observing end. The focal length of the 20-inch refractor is 28 feet. The reduced aperture and the long focal length gave details on Mars not observable with full aperture. "The diaphragm material is 22-gauge black iron. The diaphragms revolve in front of the dewcap actuated by a j^-inch steel rod extending the entire length of the tube to the observing end. Here there is a steel disk six inches in diameter with three notches on the rim into which a spring-actuated rod drops