Originally posted by Fleafly sigma 400mm f5.6 APO with 1.7X AF TC, for me was a good solution before to brought DA*300 to us with TC.
I paid 250€ fot TC and 250€ for sigma, non 500$ but a decent solution.
I have proved also PRATIKAR 500mm f5.6 but without good results
I have both lenses, the Pentax 500/4.5 and the Prakticar/Meyer Optik 500/5.6. Both are more or less en par optically (I made a lot of side by side comparisson, because I originally intendet to sell off the lesser performing one), but the mechanics of the Pentax is very much preferable, as focusing is smoother, easier and thus faster. The Meyer-Optik (or Pentacon or Zeiss Jena and I don't know, which other names they used in the GDR) serves well for medium format, where you work slowlyer, but really is a beast for a small camera.
Ben