The 0.75x reducer can bring Askar 91F's focal ratio down to F5, providing not only a faster focal ratio but also built-in field-flattening correction. The shorter focal ratio delivers a wider field of view and a faster exposure time, making it ideal for capturing large areas of nebulae, star clusters, and faint, fast-moving celestial objects.
The 91F 0.75x reducer adopts a triplet design and supports a 44mm full-frame image circle. The back focus from the M48 thread is a standard 55mm. Both end threads are M59*1. The 91F photographic extension tube includes M54×0.75 and M48×0.75 adapters for direct and convenient connection to the 0.75x reducer. The reducer features a built-in M48*0.75 2-inch filter thread, allowing for direct filter installation and use. The entire reducer is CNC-machined and comes with front and rear metal threaded caps to protect against dust when not in use.
Specifications
| Parameter | |
| （After attaching）91F Focal length | 455mm |
| （After attaching）91F Focal ratio | f/5 |
| Lens Number | Triplet design |
| Back Focus | 55mm（from the base of M48 male thread） |
| Weight | 0.3kg |
| Rear-end thread type | M59*1 |