Designed specifically for their Esprit 150 ED APO f/7 refractor optical tube, the Sky-Watcher 0.77x Focal Reducer / Flattener is an indispensable dual-purpose accessory 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/7 to f/5.4
- Reduces exposure time by 68% compared to native f/7 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
- 95mm back-focus or 55mm using the included back focus spacer and M48 ring
- 2″ filter threads for mounting filters such as moon, polarizing, light pollution, and nebulae into the light path
Field Flattener
- Reduces spherical aberrations across the entire field of view, produces flat images without curvature or streaking at the edges
- 36mm fully illuminated field, compatible with both APS-C and full frame sensors
- 3.18 x 2.12° field of view when used with a full frame camera
- 2.08 x 1.39° field of view when used with APS-C crop sensor
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