AN IMPROVED FORM OF THE WEDGE PHOTOMETER

Abstract

The Pickering form of the wedge photometer, a number of which were in use at the beginning of the century,1 may be briefly described as follows : Light from a miniature lamp passed through a pinhole and a ground-glass screen (the seeing matcher), which was movable in the direction of the optical axis of the photometer, then through a photographic wedge which could be slid along by rack and pinion to adjust the intensity of the light. From the wedge it passed through a short focus lens and a pair of neutral tint absorbing glasses, thence to a plane parallel glass plate (the field plate) set at 45° to the axis of the photometer and the telescope. Reflected from the two surfaces of this glass field plate, the light formed two images of the pinhole (one out of focus) in the field of a wide-angle positive eyepiece near the image of the star from the telescope. There were several defects in this instrument which we will discuss in