How to digitise
slides and negatives.

Size. A 35mm frame measures 36 × 24 mm, about 1.4 × 0.9 inches. Scanned at the 300 dpi that suits a print, it gives about 425 × 285 pixels, barely a thumbnail. At the Library of Congress’s 1,900 dpi it gives about 2,700 × 1,800 pixels, enough for a 9 × 6 inch print at 300 pixels per inch.

Negatives add a second job. They are reversed, and colour negatives carry an orange mask, which FADGI describes as a dye mask designed for the colour paper they would be printed on. Scanner software has to invert and correct them, so set it to the right film type. FADGI also warns that no scan can reliably show how a negative would have printed in its day, and that colour negatives made before 1975 (the C-22 process) do not scan well. Treat the colours as a starting point, and adjust a copy rather than the master.

The Library of Congress’s scanning handout suggests around 1,900 dpi for slides. Its digital preservation blog gives around 1,400 to 1,500 dpi for slides and very small prints, and a minimum of 1,500 to 2,000 dpi for negatives, with the master saved as a TIFF.

Archives go further. For 35mm slides and negatives, FADGI sets 1,000 ppi at one star, 2,000 at two, 3,000 at three, which it calls “a very good professional image that is appropriate for most uses”, and 4,000 at four. For family film, 2,000 to 3,000 dpi is a sensible middle, with 4,000 for the frames you love most. Higher settings mean bigger files:

Some scanners include Digital ICE, which removes dust and scratch marks from colour film. Epson’s scanner guide says it doesn’t support Kodachrome, works on black-and-white negatives only if they are chromogenic film, and can make images look softer. For Kodachrome and ordinary black-and-white film, use the software’s standard dust removal, or retouch a copy.

Kodak introduced Kodachrome in 1935 as the first commercially successful amateur colour film, and 35mm slides followed in 1936. Kodak’s Carousel projectors arrived in 1961 with a round tray that held 80 slides. Kodak announced the film’s retirement on 22 June 2009, after a 74-year run, and the last rolls were processed at Dwayne’s Photo in Parsons, Kansas, on 18 January 2011.

All colour film changes in time. The Canadian Conservation Institute notes that dyes in colour photographs appear to be the only materials in a visual art medium to fade appreciably in the dark, and that faded colour photographs are thought to be impossible to restore chemically. Films differ, though: Henry Wilhelm’s research, as summarised by the US National Park Service, puts Kodachrome among the most stable slide films, as long as it isn’t projected often.

Projection is the other risk. The National Park Service’s advice for museum collections is to use copies, never originals, for slide shows, and not to project an image for more than 30 seconds. Scan the slides before anyone runs the projector again, and use the files for the next family slide show.

Cool, dry and stable. The Library of Congress recommends 30 to 50% relative humidity and 21°C (70°F) or below for photographs generally, and 4°C (40°F) or below for colour photographs and film negatives, where temperature controls how long they last. It also advises against lofts, cellars, radiators and outside walls.

The Image Permanence Institute’s figures show why cool matters for acetate: fresh film kept at 21°C and 50% relative humidity is predicted to reach the onset of vinegar syndrome in about 40 years, and at 16°C and 40% in about 100. Once film has channelled or turned brittle, nothing reverses it.

Our guides to storing old photos and how long photos last go into more detail.

Once the slides are scanned, upload JPEG copies to your family Library on the Ancestorii website and give each carousel, box or holiday its own folder with a name, a description and a date. Then turn the best into family photo albums, where relatives add who is in each frame, the year, the story and a voice note.

A slide show used to need a projector and everyone in one room. An album can be opened by everyone you invite, wherever they live. Albums are unlimited on every plan, and storage is shared by the whole family: 1 GB on the Free plan, or 100 GB on Premium at £3.99 a month per family. Keep the TIFF masters and the film itself in your own care.