20mm Huygens No-name
Within of 20° field of view very good.
x-axis: distance from optical axis in °, y-axis: resolution in arc minutes
Apparent Field of View:
As small as 25°. Really an eyepiece with a tunnel feeling.
Bad. No lens coating.
Without any problems in use.
Very simple manufactured, e.g. loss of coating (paint) after some use.
Good sharpness is the only pro. All other points are far away from a recommended use for astronomical purposes.