At the first time I thought this lens a cheap and crap Japanese lens like Soligor,Hanimex, Porst etc. That was wrong this lens surprised me really.
Lens very sharp even at wide open, it has good color rendering. Seems good deal, only the problem not appear frequently on the market, pretty rare item. I will sell out after testing because not fit into my collection lines. No manual switch on the lens body it has only fully automatic aperture handling, this is a problem if you want to use on DSLR bodies. You have two choice, look forward a right M42 adapter, what can handle auto aperture stick or use some strong glue and solve this problem for ever with glue :) What can I say more this lens has same quality than best ones in 135mm category like CZJ Sonnar 135mm or Super Takumar 135mm,perhaps comparable with Canon or Nikon equals too.
No reason to modify the lense as adapters which push the preselection pin are easily available.