Optically, the lens is of conventional double gauss design. This is a good thing - lens designers have had a long time to perfect the double gauss, and most normal (50mm or so) lenses are based on it. This lens gives excellent performance at stops, with the optimum stop being at f/4 or so. At f/1.4 it has a very slight softness, which is gone by f/2. This is completely expected and ordinary for any fast lens. It does exhibit some coma, being a double gauss. This is fine by me - if I need a fast coma free lens, I suppose I'll pony up for the Nokton 35.This lens stays on the R-D1 about two thirds of the time. It is a bit longer than normal at an effective focal length of 60mm, but I adapted pretty quickly to the field of view. The only real down side to it is the bright chrome front ring. I bought this lens sight unseen like the rest of my CV lenses, and am very pleased with all of them, especially the Nokton. It is a pretty good match for 35mm framelines.
It might not seem very special at first glance, but the 40mm is a somewhat rare and coveted focal length. This one is a full stop faster than any other 40 that I am aware of for full frame 35mm use. Go ahead and compare this lens to the Leica 35 f/1.4 - the Leica will probably be sharper wide open, and have a bit more correction for aberrations, but for 8x the price I would expect it to give backrubs as well.
If any of you out there in bitland are thinking of getting a 35mm lens, look at this 40 before you decide. The FOV isn't really much different, and you will be pleased once you get it.
