Helios 44M 58mm f/2

Unlike most of the Russian lenses this one is actually quite stunning. The Helios 44's are copies of the legendary Zeiss Biotar 58mm f/2 with the only real differentiating factor being a simpler aperture mechanism on the Helios lenses. However unlike the original Zeiss lens which is a little rare and can be expensive the Helios 44's are incredibly common and very affordable. The lens is very sharp in the center and has amazing out of focus rendering. The corners are soft but this lens isn't meant for landscapes - it's meant for portraiture. It can create an amazing ethereal feel that is impossible to recreate with modern optics. I got mine for a good price in great condition from eBay. As usual with these vintage Russian lenses be careful when purchasing but unlike the others which I feel are only collectors items this is a serious photographic tool. There's really no reason not to own one if you have a camera that can have M42 lenses adapted to it.