Designed specifically for their EvoStar 72ED f/5.8 refractor guidescope, the Sky-Watcher 0.85x Focal Reducer/Flattener is an indispensable dual-purpose accessory that allows you to use it for astrophotography and astroimaging. The field flattener corrects the inherent spherical aberration of curved lenses which, if left uncorrected, causes images to appear distorted at the edges of the field of view. As a focal reducer, it reduces the focal ratio of the scope which translates into wider fields of view with shorter exposure times—allowing you to capture more images in the same amount of time without sacrificing performance.
Focal Reducer
- Decreases the f/ratio from the optical tube's native f/5.8 to f/4.93
- Reduces exposure time by 38% compared to native f/8 with the same results
- Reducing exposure times allows you to capture more images in the same amount of time with the ability to use different filters to produce better images in post with stacking techniques
- 55mm back focus distance
Field Flattener
- Reduces spherical aberrations across the entire field of view to produce flat images without curvature or streaking at the edges
- Compatible with both APS-C and full frame sensors, although APS-C (crop sensors) and smaller are recommended
- 5.8 x 3.87° field of view when used with a full frame camera
- 3.79 x 2.53° field of view when used with APS-C crop sensor