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Film Scanner Problems

Holding film flat

When scanning film, one major problem is in holding the film flat. Designing good negative carriers is surprisingly difficult, and all of those I've used have their problems. Slides are often scanned in their mounts, and only glass-mounted slides are ever flat across the whole slide.

As with enlargers, few negative carriers are designed to show the entire negative frame, giving slight cropping at the edges. If you want to scan full-frame you may need to perform some very careful opening out of the apertures with a suitable tool. Getting replacements for negative carriers should you damage on can be a lengthy business. I've had one on order from the UK distributor of my film scanner for several months with no success. Fortunately I still have one in working order and am waiting for the replacement to modify for panoramic scanning.

Glass or glassless film carriers?

Using glass in a film carrier also improves sharpness, but at the expense of adding 4 surfaces to keep clean and dust-free. If clean, they may also produce interference patterns - called 'Newton's Rings' with the film base in close contact, and are sometimes produced with a finely ground surface to prevent this, which may add a very slight texture to the images.

Dust Problems

Dust is a major problem in scanning, more so than in enlarging because most scanners make use of highly focussed point light sources which show off every blemish. If you've ever used one of the fairly rare point-source enlargers you will be aware of the problem. Diffuser enlargers make life much easier in the darkroom.

A typical high resolution scan from 35mm - even if care is taken in cleaning the negative and carrier glasses (if used) may take 25 minutes work to clean up and remove all blemishes. In Photoshop the healing brush and the clone stamp are the main tools to use. Anything that can reduce this amount of work is important.

Diffuser

Recently two leading members of the Minolta Dimage Scan Multi-Pro user group came up with the simple idea of adding a diffuser to the negative carriers of this scanner. The improvement it gives is impressive, not only in reducing dust but in giving less 'noisy' scans but retaining the same level of detail. The Scanhancer they designed is available cheaply. Although it is specifically cut to size for the negative carriers for this scanner, it may be worth trying the same principle with other scanners.

Minolta have independently been working on the same principle, and have incorporated it in their latest 35mm scanner, so you can expect this to become common practice. Other scanners may already be designed to have a diffuse light source, and so avoid the worst of the problems.

Digital Ice

Another clever aid in beating dust is the use of an infrared scan channel. Infrared is little absorbed by the dyes in most colour images, so produces an image that is mainly due to dust and other film blemishes. Software can then be used to subtract this noise signal from the other channels. Digital Ice is very effective, but only works with colour films, and cannot be used with Kodachrome. You need to be careful in using it, as excessive filtering will also remove image detail.

Dust and scratch filters can be designed in software, but their use is limited as if applied strongly enough to remove most dust they also get rid of much image detail.