Skywatcher Ultra Wide Angle 20mm
Very good sharpness within 55° apparent field of view, but gets a bit worse close to the edge.
x-axis: distance from optical axis in °, y-axis: resolution in arc minutes
Apparent Field of View:
The apparent field of view is approx. 63°.
Very good contrast.
Very slight cushion distortion.
Not too easy. You will need some practice in finding the correct distance where the center as well as the edge provide a sharp image at the same time..
Good quality with foldable rubber eye cup.
A nice wide angle eyepiece, but a minus for the eye relief. At F/5 you will see noticeable aberration close to the edge. Recommended for F/6 or slower.