The subject is viewed through the small central eye-piece, turning the case causes a variable density wedge to slide over the field of view. When the indistinct point is reached a value is read from a window on the front of the meter, this is used to look up the shutter speed / aperture pairs from a table printed on the front of the meter. In bright conditions a filter can be swung into the field of view. The early Aktino-Photometer was well-made but its mechanism and construction was over complicated for an extinction meter. The price in 1905 was 17/6.

Rotating the case of the meter turns a blue variable density wedge. At the extinction point a series of shutter speed / aperture pairs can be read.