Although the process I'm using involves copying 35mm negs with a digicam instead of a scanner, this is really a question about the optics, not a hybrid process.

I use a +2 close up lens in front of the digicam lens, which fills the frame. When I copy the negs I get a fairly usable image, but the sharpness deteriorates horribly from the center to the edges...especially the 36mm axis.

I'm assuming that's due to the close-up lens degrading the image toward the edges. Would the use of a step-up ring (say 52-67mm) and a larger +2 close-up lens help the situation? Thanks!