What is the optimum scanning resolution?
That depends. If you intend to use the scan to make 4 x 6 prints, a resolution of 1370 DPI (cropped) will capture all the image data 35mm film has to offer at that print size. If you intend to make 8 x 10 prints, then the negative or slide will have to be enlarged or magnified more to cover the larger print area. Consequently, 8 x 10 prints require a scanning resolution of 2662 DPI (cropped) to yield the same print quality as a 4 x 6 print at 1370 DPI. If you’re like most of us, you don’t have a crystal ball and have no idea how you might want to use a scanned image sometime far off into the future. To play it safe, you could have us scan all your slides and negatives at 4000 DPI, and if you intend to use the scan for many purposes, that’s probably the way to go. But realistically, that would be overkill in some cases. We recommend that you have your best slides and negatives (the ones you value the most) scanned for a 12 x 18 print size or at 4000 DPI (same resolution in both cases) a
