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Don't be fooled when you're picking a film scanner
 Film scanner specs can be confusing. Worse, marketing people sometimes want to make them that way: if you don’t know how to read ’em, you risk thinking a cheap scanner’s better than it really is. So it makes sense to figure them out. Here are explanations of the three most stultifying specs: resolution, D-max, and bit depth. Read this, and no salesperson can play you for a fool.
> Resolution
What it is: Resolution is measured in dpi, or dots per inch, a.k.a. ppi, or pixels per inch. In this case (but not so of printers), dpi and ppi are the same thing. The more dots per inch the scanner can sense, the more detail it’s capable of capturing, the larger your file size, and the bigger the potential size of your printed image.
Reading the Spec: Scanners have two numbers defining their resolution: optical and interpolated. Optical measures the maximum number of actual dots the scanner can record in every inch. If you’re trying to figure out what kind of quality a scanner can capture, pay less attention to the listing of interpolated resolution. A scanner uses interpolation software to add data post-scan and output a larger file, but it’s not true recorded information. Beware: manufacturers sometimes try to trump up their numbers by emphasizing interpolated over optical resolution.
What you need: A 4000-dpi scanner can capture nearly all of the information in a supersharp 35mm negative or slide. A 5400-dpi scanner won’t miss a grain. But the less expensive scanners (typically 2800 dpi) still work great for prints up to 13x19 inches.
> D-max
What it is: D-max is the number that points you toward an understanding of the scanner’s dynamic range, or the its ability to discern and reproduce levels of brightness in the shadows and highlights.
Reading the Spec: A D-max rating of 3.2 is good (about equivalent to a typical slide film’s abilities), but a higher value, such as 3.8, may capture increased shadow detail in a contrasty slide. Don’t be fooled by the squatness of the scale; D-max is measured logarithmically, so the difference between a good scanner and a very good scanner doesn’t appear enormous to the nonmathematician.
What you need: Only the better scanners list the number, so no D-Max rating means you won’t have much luck scanning your T-Max. A higher D-max is even more important in a film scanner, and these days great consumer scanners can have ratings of 4.0 and higher.
> Bit depth
What it is: This figure shows the number of colors, or shades of gray, that a scanner can differentiate. A greater bit depth yields smoother continuous tones.
Reading the Spec: The higher the bit depth, the more colors a scanner can read, exponentially. A 24-bit scanner (average) can differentiate 16.7 million colors (eight bits, or 256 shades, each for the red, green, and blue channels). A 48-bit scanner (awesome) can discern billions of colors.
What you need: The best scanners can scan up to 48 bits per color. If you’re serious about making prints, you should go with a model that captures at least 36. On the other hand, if your focus is monitor-viewing, a 24- bit scanner is just fine.
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