In scanning, DMax is a term used to refer to the maximum density that a scanner can see detail in. It’s useful because it can give you an idea of the potential dynamic range that a scanner is capable of recording. The higher the DMax, the better the scanner is at penetrating the darkest areas on a photograph, and therefore the greater its dynamic range.

While it is a useful figure, it only really becomes important when your aim is to scan transparencies. This is because the orange base of a colour negative and the grey base of a black & white negative immediately reduce the dynamic range of negative films, as there is no ‘white’ in either. This effective reduction in the contrast of the film makes it much easier for a scanner to record the full tonal range in the image. However, slide film has a transparent base that can be seen as pure white. Therefore, when you make a scan to retain the highlight areas in a slide, the DMax is the determining factor in how much detail is recorded in the darker areas before they are simply seen as black.

Generally, a DMax of 4.0 is seen as the value that will accommodate even the most contrasty of slide films, therefore scanning as much highlight to shadow detail as the film itself can record, but this comes with a significant caveat. The DMax figures given by scanner manufacturers are ‘theoretical maximums’, rather than measured values. So, while DMax can be used as a guide to a scanner’s potential dynamic range capabilities, it is by no means absolute.


I have a collection of old 35mm slides and negatives that I would like to digitise to ‘library’ standard. Some of the photographs were taken by my late father and have some historical interest. I’m not talking about digitising a huge collection, more a case of selecting images of particular interest. I am happy to take my time to get quality results. If my understanding is correct, this would be a job for a dedicated film scanner with a minimum dynamic range of 4.0.

My budget is around £300, which obviously excludes very high-end professional scanners, so could you tell me what kit is available to cope with this task? I have considered using a scanning service, but would prefer not to send the material off to third parties as I would like to have control over the whole process myself. Mike Village

I suggest you aim for high-resolution files of around 50MB when you scan the film. Although this is larger than the minimum size requirements of many image libraries, it will mean the images could be printed at 300ppi to A3 size.

You will need a scanner with an optical resolution of at least 4000ppi to achieve this. If you want to buy new, then Plustek’s OpticFilm range of dedicated 35mm film scanners offer resolutions far in excess of this (7200ppi) at £200-£350, depending on the model. However, while the optical resolution is high, the DMax (see Glossary, above) is not: all current 35mm OpticFilm scanners have a DMax of 3.6.

For this reason, I suggest that a slightly older ‘premium-priced’ model will give you far better results. Models to consider include the Nikon Coolscan V ED and Coolscan 5000 (pictured), as well as the Minolta Dimage Scan Elite 5400 and 5400 II. Although these were discontinued years ago, they are still three of the finest 35mm film scanners ever made. Each has the optical resolution needed to create a 50-60MB file size from 35mm film (the Coolscans are 4000ppi units, while the Dimage 5400 has a 5400ppi optical resolution), and all three have a DMax that will prove a match for the vast majority of slides (4.2 for the Coolscan V ED and 4.8 on the Coolscan 5000 and Dimage 5400).

The downside is that these scanners are no longer in production. Looking at eBay’s ‘sold’ listings for these models reveals that they all pop up from time to time, but despite being ‘obsolete’ the Dimage 5400 and Coolscan V ED still sell for £400-plus, with the Coolscan 5000 the only one that is around your £300 budget.

You would also probably need to budget for scanner driver software, as none of the manufacturers supplies drivers that are compatible with modern Windows and Mac operating systems.

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