A common question from those with large collections of photographic slides (transparencies) is could I use a slide copier to digitise my collection of slides into my iPhoto/Photos library?
A Yes: slide copiers such as the Ohnar, which costs well under £100, are a good alternative to a dedicated slide scanner (now very hard to obtain) or a flatbed scanner with film carrier.
Slide copiers mount on the front of a digital camera; most, like the Ohnar, screw into the front of the lens, and you will need to check that your camera and lens have a suitable thread. They provide more accurate registration, which saves time when scanning, and when equipped with a film strip or other carrier you can ‘scan’ several slides per minute.
You need to provide the far end of the copier with a bright and even light source, which could be from bounced flash or a continuous source of a suitable colour temperature.
Those who have used this technique generally get slightly less crisp results than from a high-end scanner, and high contrast slides can exceed the dynamic range of the CCD in their camera. The latter can be alleviated by adjusting lighting carefully.
Unfortunately, whilst this can work well with monochrome negatives, it does not help with colour negatives.
Updated from the original, which was first published in MacUser volume 28 issue 14, 2012.