The Prismeter was a very neat solution to the problem of parallax on rangefinder cameras. A number 2 model was also produced as well as models for other cameras.

The calculator is first set to the size of the object, windows for each lens then show the extra extension required, the exposure value increase in EV and the lens-to subject distance. Another window shows the magnification and the depth-of-field at f11. On the other side of the calculator, windows for each lens show which accessory will be suitable (Proxar, tubes, bellows). There is a separate scale to convert EV values to shutter speed / aperture combinations. The scales are for lenses of 80, 100, 110, 120, 135, 150 and 250 mm focal length.