[davidmanze]

What sort of terrible is it and what apertures were you shooting with?

 Remember that these types of lenses were nothing special at large apertures.....the Pentacon 135 F2.8 was a fringer wide open.......but improved to very good on stopping down:

[photonius]

Worst lens:
A 300mm mirror lens, Canon FD mount, around 1980. Can't remember the brand, Miranda? Or maybe it was a Tamron (don't think so). Not Canon, Nikon, Pentax, Sigma, Minolta, Vivitar...
I don't think I got one good shot with that (no auto-ISO days...), it was soon replaced with a newly released Canon FD 70-210 f/4 which was more useful (though probably not the "best" lens either).


Edit: maybe it was a Makinon 300mm f5.6

[toni-a]

What sort of terrible is it and what apertures were you shooting with?

 Remember that these types of lenses were nothing special at large apertures.....the Pentacon 135 F2.8 was a fringer wide open.......but improved to very good on stopping down:

First it comes in contax/yashica mount and has camera driven aperture so no manual  aperture dial, I have to remove it from mount to change aperture without having a clue at what aperture I am using it, second I tested it only at f4 and nothing impressive sharpness wise,   Sony 50-210 that I don't consider as a sharp lens  is sharper although a little bit slower.
Besides it's an old lenses and didn't like the colors especially in contra light, so why carrying a manual focus lens with its adapter with so many limitations when it is easily outperformed by a lightweight zoom with autofocus ?
I kept the 44-2 58f2.0 just for the special bokeh despite all its shortcomings, Sony adapter has infinity focus, I have two canon adapters one with infinity focus the other one without it acts  practically like an extension tube, swirly bokeh in macro is sweet to have.
The Jupiter has nothing special to offer