An antique scale on a wooden shelf.

What to weigh for slide scanning

While I was working on a 35mm slide-scanning project, the client asked me about printing from the scanned images. Would the scanned images yield quality prints?

Many factors impact the quality of a scanned image. First of all, what was the quality of the original image, and what were the film characteristics? These factors are no longer within our control.

Factors we can influence at this stage include the resolution the slides will be scanned at, preparation of the slides before scanning (dust removal, etc.), and adjustments (e.g., color) performed as part of the scanning process.

For 35mm slides, scanning at 2000 DPI (dots per inch) is the minimum recommended; the maximum is generally 4000 DPI. Scanning at a higher DPI takes longer (and is therefore more expensive if you are paying for the service). Higher DPI also yields larger file sizes (a potential storage expense).

My client weighed the desire to keep file sizes manageable and the cost of digitization reasonable with the possible need for a select number of prints. He estimated that he may want a small number of slides (30 at the most) as 5×7 or 8×10 prints. Our solution:  we agreed to scan all slides at 2400 DPI, as the vast majority of them will be viewed on a computer or mobile device. For the small number that may be printed, we will scan only those slides a second time, at a higher DPI. It just did not make sense to scan an entire collection of slides (over 1,000) at a higher resolution, when only a few dozen may eventually be printed. The client reviews the images after each set of slides is scanned, so he can identify any slides requiring a second scan during the review.

General guidelines for 35mm slide-scanning resolution if prints are desired:

Scan Resolution (DPI) Best For Print Size (Inches)
2000 5×7
3000 8×10
4000 11×14

Additional tips:

  • Consider scanning only a select number of slides at one of the higher resolutions.
  • Some scanners allow the user to specify a target size (e.g., 5” x 7”) for the scanned image and will adjust the resolution accordingly.

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