I have accumulated several thousand slides and 35-mm negatives that I'd like to digitize. Is there any good reason to invest in a slide scanner that I'll never use again, or does it make more sense to get a flatbed with high resolution and a slide-scanning feature? Also, what resolution should I be looking for?
Solution Given the number of slides and negatives you have, I'd argue that a good slide scanner, also known as a film scanner, is worth getting. One reason is resolution. At the risk of oversimplifying, for best image quality you need an image resolution of at least 300 pixels per inch (ppi) at the size you're printing. For a 35-mm original printed as an 8-by-10 photo, that works out about 2,200 ppi for the scan. Scanning at higher optical resolution is even better, in case you decide you want to crop the image.
You can find flatbed scanners with sufficient claimed resolutions, but they often don't live up to their claims—typically because of the limitations of the optics. But any decent slide scanner will provide the resolution that slides need, because slides are its primary function, not an extra.
You also need to consider dynamic range—the scanner's ability to record details over the entire range from the darkest to lightest shades. Almost any slide scanner will do a better job on this than almost any flatbed scanner. Keep in mind, too, that slide scanners generally make the scanning procedure a little easier. With thousands of originals to scan, even the smallest convenience will make a big difference over the course of the project. [Via]
