I've had the Biogon since Christmas and have used it quite a bit. It's a very good lens in terms of sharpness, size (the summicron is too small for my hands), flare resistance, color rendering, build quality, and price.
That being said, it's just kind of a 'meh' lens for me. It's technically good, but a little lacking in character.
This is only my opinion, though.
For B/W work it's too contrasty for the developer I use, so the success rate of my shots is affected. I do occasionally get lucky.
Also, the OOF rendering is pretty hit and miss. I find its wide open performance good for some situations.
and pretty garbage for others (I hate the doubled lines).
Also, lights in the background take on very oblong shape with a distracting hard ring around the edge.
To my eye, the best 35mm I've used is the Nikkor f/1.4 Ai-S for Nikon F-mount. It's super sharp, the OOF areas are smooooth, and it has this amazing 3-D effect that really makes the in-focus parts jump out of the background.
I don't think this was very helpful, but in summary, the Biogon is good, but a little dull.
That's just my opinion and I could understand if people thought otherwise.
