Update: I have written more about this lens here: Nagano, Japan: through the Summicron 50.
Formerly I owned the V4 and V5 Summicrons, both lenses slightly sharper than the V3, and both with harsher OOF elements, which led me to sell them. This lens has the wonderful ergonomics of the V5, but is small and light like the V4.
For some reason it is less popular than the V4. My wallet is glad.
Being an older lens, I didn't expect so much contrast and quick falloffs to black, but the V3 surprises. It is also extremely quick to focus. I am able to focus it almost as quickly as I can the 50/2 Nikon Ai lens on a large-viewfinder SLR camera. I suspect the slight delays inherent in focusing the M240 and V3 Summicron and the D800 or FM and 50/2 Ai are down to my prescription.
I must upgrade that.