...does anyone have expirience with mirror lenses?
Frend has M42 Rubinar 500mm/5.6 (only f5.6) lens in pretty good shape for cca 200$. For that money, I will also get 2x converter.
With this converter and crop factor, it will give me 1600mm.
Is it worth that money. Bundle also includes some 3 filters for sun and moon shooting (don's know specs).
It looks like this:

It has tripod mount ring at the bottom.
I never even knew that something like this even exists.
Please few advices, thx.