|
The Takumar 200mm f/2.5 should not cost an arm and a leg. Given it will probably be used wide open, number of diaphragm blades, being a screw mount or being manual aperture only is of no consequence. The Pentax 200mm f/4 , although slow, will be plenty sharp enough(and cheap). With astro, best to avoid zooms for 3 reasons.They are slow, sharpness not as good and extra elements lead to internal flare issues.Screw mount lenses are cheap and can be adapted to basically all lens mounts. Needless to say nothing automatic is going to work.
|