I've been researching this for the last few days as I have a graflok to V back convertor on its way for my 4x5 camera / CFV II 50c. The issues seem to be:
- Colour fringing - Due to the nature of a digital processor sensor pixel layout (2 dimensions) versus film colour layers (3 dimensions)
- Difraction - Large format lenses you typically stop down to f22/32/45 with film, If you do that with the digital sensor you're going to get diffraction issues
- Crop factor - A wide angle 4x5 lens is a normal or even tele when used with a 33x44mm digi back
I haven't managed to *find* any useful examples of the above online, so when my convertor arrives I will shoot some test shots before I decide to get any digital back optimised large format lenses. I don't know if the issues are more pronounced when using movements (I suspect yes?) and will test that also, as that is my primary reason for wanting to use the CFV II 50c on my 4x5 camera.
Follow up on this - received my graflok to V back.
I shot this frame using my 4x5 camera with my Schneider Super-Angulon f5.6/90mm on Fuji Acros:
I then switched my film back with my digital back. The crop factor when using the CFV II 50c back looks like this:
I can use the back's built in shift combined with the rise/fall of the front standard to get a stitch of 9 frames eqivalent to this:
The resulting stitch:
Here are some 100% crops from that, none of which have been sharpened:
Bottom left corner:
You might notice some slight colour changes at the edges, which brings us onto the next thing:
I'd say on the 90mm (and longer) it's more than acceptable. If I stick my 72mm on and use the back's shift to do a 3 frame pano, then we get a clear indication of how wide angle large format film lenses will be a problem on a digital back:
I think a general rule of thumb is the closer to the back standard the worse it will be. I think the 90mm is more than acceptable, I wouldn't hesitate to use it with stitching and movements.
The last thing:
Yes, this is a problem. Here's some 100% crops from the CFV + 90mm
I didn't test all apertures so I don't know if f11 is optimal.
In terms of general sharpness the 90mm on my CFV II back is more than good enough, even at the edges with the stitching. I doubt I will bother getting digital optimised large format lenses.