Jim Leonard , Aug 24, 2001; 02:46 p.m.
Assuming you are using 35mm slides, if you are using the full frame to produce your printed image, the 2500 dpi scan will give you about 300 dpi at 8x10 which is considered ideal. However, if you are cropping significant amounts of the original image or printing at 16x20, you are quickly dropping down to 150 dpi of non-interpolated pixels (ie 1/4th the information density). This is where the 4000 dpi scanner becomes useful. Personally I only use digicams (where pixels have less value per pixel since each pixel only starts with 1 chroma and gets the other 2 from it neighbors) so the required numbers would be a bit different than if I were scanning film but in my (very limited) experience, I don't like printing with much less than 200 dpi of original pixels for anything with significant detail.