I'll throw in my thoughts regarding some of the 28mm lenses mentioned here...as those I have used, I've tested exhaustedly, mostly on a full frame digital Leica. The cron Ver. 1 has very even sharpness across the entire frame (edge to edge and corner to corner) but its sharpness is gentle, not biting and of very good contrast. if I was to nitpick, the corners were a bit less in resolving power than the other parts of the frame. The Elmarit asph is bitingly sharp and very high contrast and that high contrast can sometimes be an issue, especially on digital cameras where highlights can be easily blown. The biting sharpness is also basically good edge to edge.
The Ver IV elmarit often displays softer corners than the Ver I cron and that to be is the primary difference. The same is also true of the Konica 28mm f2.8 (soft-softer corners than the Ver I cron)….therefore I can see why many feel the Ver IV Elmarit and Konica are of similar design. The Ver. II cron corners are the sharpness of the lenses I've mentioned so far. I actually love the Konica and those soft corners draw the viewer towards the central part of the frame.
Now onto the 7-Artisans 28mm f1.4. Its of course much bigger and heavier than all the other 28mm lens mentioned and actually is about 80-85% of the performance of the very expensive leica 28mm f1.4 Lux...at a ridiculous fraction of the cost of any of the lenses mentioned. Focusing control is well dampened but as was just mentioned, the aperture ring is whole f-stops and not evenly spaced. Optically its even quite good wide open at f1.4 and at f2.0 has wonderful performance across the entire frame...sharpness as well as contrast. The trick to getting this performance from this lens, is the ability of the user to adjust focusing of the lens with the simple screw driver supplied (easy with a digital camera for easy review). Its almost mandatory to do this upon receiving the lens.
Dave (D&A)