20mm Huygens No-name
Sharpness:
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.
Contrast:
Bad. No lens coating.
Aberration:
-
Eye Relief:
Without any problems in use.
Mechanical Quality:
Very simple manufactured, e.g. loss of coating (paint) after some use.
Summary:
Good sharpness is the only pro. All other points are far away from a
recommended use for astronomical purposes.