Description
Askar provides a brand-new F3.9 full frame reducer for FRA400/FRA500 astrograph, further reducing the focal length and thus shortening the exposure time on its original 400 focal length and f/5.6 focal ratio design basis. The reduction factor is 0.7×, and the reduced focal length is 280mm, which can satisfy most deep-sky astrophotography. The back focus is standard 55mm. The reducer has built-in M48×0.75 thread, easy for the attachment of 2" filters.