We had a thread on this about a year ago, quite a lot of info on that.
I mentioned some success with snapping prints and negs with a D SLR, believe it or not. Got some quite good results. With negs, the back light was very crittical however, and for the experiment I used the lid light of my scanner.
Pegging up to the window gave the best light, but needs a sheet about four feet from the glass to eliminate the pattern from trees etc. Tripod and timer were essential of course.
It takes one heck of a scanner to create a 4 M file in a fraction of a second.
Using a cheap scanner Epson 3170 from Epson refurbished sales ($70), I got results that were nearly as good as a more expencive unit.... $450 ish. Trouble with photography, is that 'nearly' isn't good enough and the lust for better kit is a somewhat cronic condition is it not?