I use a 903 SWC with a P25. It performs very much like it does with film, ie very good sharpness, excellent distortion, very poor vignetting. Subjectively the vignetting appears worse with digital than film, but of course it's also easier to correct with software. The virtually zero distortion is the main reason I keep it. In terms of sharpness I find it marginally better than with my Rodenstock Apo Sironar Digital 35mm on a Linhof M679cs, but there's no lens movements possible with the 903 SWC. I also use the relatively new Hasselblad 40mm IF, this lens has superior sharpness and much lower vignetting, it can also be used on a Hasselblad Flexbody with a fair amount of shift and tilt capability, however the distortion is probably the worse in the entire Hasselblad line up...you pays your money and you takes your choice!
The biggest issue I find with the 903 SWC and digital is focussing. On the one hand the 38mm Biogon has exceptional depth of field. This is a controversial area but I'm convinced different lenses of the same focal length can deliver both different real and apparent depth of field characteristics. Some time ago the Marketing Director of Zeiss was a regular contributer to Photonet, he spoke at length on this topic, and supported by the full optical experience of Zeiss his was a voice that deserved some attention! His claim was that the 38mm Biogon offered exceptional real depth of field, where as many other lenses of about the same focal length and carrying the same depth of field engravings, had considerably smaller practical DOF (for interest, he also claimed zoom lenses tended to have poor DOF characteristics). My experiences with the Biogon compared to the above mentioned Rodenstock 35mm and Hasselblad 40mm supports his view. I suspect a lot of the 903 SWC's towering reputation is based on this extended DOF.
On the other hand the 903 SWC needs an extended DOF partly because it operates on scale focusing, unless of course you slow the whole thing down by using a ground glass back. Again it's a personal view but in my opinion scale focusing and digital don't make particularly happy bedfellows. Even with the DOF characteristics of the 903 SWC, realising the full potential of modern digital photography often requires precision focusing, and scale focusing just doesn't cut it if you're looking for the absolute best results.
