5mm Huygens No-name
Sharpness:
Terrible.
x-axis: distance from optical
axis in °, y-axis: resolution in arc minutes
Apparent Field of View:
As small as 31°.
Contrast:
Worst I have ever seen. No lens coating.
Aberration:
-
Eye Relief:
Very short eye relief makes it difficult to look in.
Mechanical Quality:
Very simple manufactured, e.g. loss of coating (paint) after some use.
Summary:
Take the sleeve, if you have need for that. Dispatch the remains – strictly
recommended.