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