The internal lens does not use a pop out design and a fixed 28mm threaded lens mounting ring was included at the front. The diameter of the mounting ring happens to coincide with that of most clinical microscopes, resulting in the 9xx series becoming popular for hand-held eyepiece-projection photomicrography. This mounting ring is present on the entire series, making them system cameras; a set of intercompatible telephoto, wide-angle, and fish-eye converters were available, and worked on any of the 9xx cameras.
The internal lens design does not use a pop-out mechanism, and a fixed 28mm threaded lens mounting ring is included at the front. This ring's diameter matches that of most clinical microscopes, making the 9xx series popular for hand-held eyepiece projection photomicrography.  This ring is present on all models in the series, making them system cameras; a set of intercompatible telephoto, wide-angle, and fish-eye converters were available, and they worked with any of the 9xx cameras.