The Askar 0.7X Focal Reducer is designed specifically for the 80ED refractor. By adding this reducer to the optical chain of your telescope, the focal length will f/4.9 for a wider field of view and faster imaging times. The reducer features a triplet optical design that includes one ED element. It is designed as a focal reducer but also provides some field flattening correction. This Askar 80ED 0.7X Reducer is optimized for the APS-C frame. The body is CNC machined for a long life and has metal caps on both ends to protect your optics when not in use. The rear adapter has built-in M48x0.75 threads that accept 2" filters. No need for a filter drawer! Finally, a 360º camera rotator is integrated into the design for easy image framing. Specifications Focal length 392mm, once attached to the 80ED Focal ratio f/4.9, once attached to the 80ED Optical Design Triplet with one ED element Image circle APS-C Back Focus 55mm from the base of M48 male thread Weight 0.32kg Rear-end thread type M54×0.75 M48×0.75 (M48×0.75 filter thread inside)