Film scanners are available used for $100, but for pro-quality results, you’ll want one of the higher-end models. There are two basic types of scanners, dedicated film and flatbed. The latter operates somewhat like photocopiers, and can do prints as well as slides and negatives. Dedicated film scanners do a better job with negatives and transparencies, but can’t scan prints. We’ll look at both types in a bit, but first, here are some general scanner considerations.
Scanner manufacturers provide resolution figures for their products. The important one is the optical (hardware) resolution; that’s the maximum the unit can deliver without quality-reducing interpolation. Some scanners have different optical resolutions, depending on the size of the original you’re scanning: higher for 35mm, lower for 120.
More resolution (more ppi) means you can make bigger prints without seeing the pixels. But take into consideration the size and quality of the original being scanned: The scanner can’t pull out more detail than the original image contains.
Most higher-end scanners can deliver 48-bit scans (16 bits each in red, green and blue channels). This means, in theory, that they can deliver up to 65,536 different shades of gray or color tones—better than the 16,384 tones of a typical 14-bit DSLR, and way better than the 256 tones of a JPEG image. In practice, the number of tones will be less, but still sufficient to accurately reproduce a transparency or negative.
Manufacturers list the maximum density their scanners can deliver, which affects dynamic range. These figures should be taken with a grain of salt, but higher is better, and you should look for a scanner with a Dmax of at least 3.6. A higher Dmax means potentially smoother gradations and better shadow detail.