The backfocus is the standard 55mm. It comes with three thread adapters of M68, M54, M48 , so it is convenient for connection.
Askar’s new-launched 3” 0.7x full-frame reducer adapts for 107PHQ & 130PHQ.
It has a triplet design with one ED glass.
The 0.7x reduction gives 107PHQ a shortened focal ratio of 4.9 and a shortened focal length of 524mm.
This reducer, connected with the astrographs, can effectively shorten the exposure time and dramatically increase your field of view, bringing more convenience and possibilities for your deep-sky astrophotography.