If you are using a scanner which will not achieve 26MB without interpolation then you need a better scanner, sorry.
Don’t try scanning transparencies on any old desktop flatbed scanner with a transparency attachment. Whatever resolution they say they will do they are generally not good enough. We have recently replaced an Epson Expression 1680 and a Polaroid SprintScan 45 with an Epson Perfection V700 which we are using for 5x4 transparencies, it is not quite as good as the Nikon Coolscan for 35mm’s but you will get perfectly acceptable results off medium and large format film. The two pictures below are details of a 6 x 4.5 transparency scanned at 300dpi to 575% giving a file of approximately 26MB, no sharpening has been applied. I think this illustrates why a dedicated transparency scanner is necessary. The Nikon is no longer made and the only desktop film scanners these days seem to be the Imacon’s starting at about £7000, but some of the flatbed scanners now available are really good. If you are getting a scanner read as many reviews as you can find, don’t just buy the cheapest. (Picture: Hackney Empire by Oliver Benn)
Make sure your scan is properly cropped and is straight. Level the horizon! We do not want scans with black frames round them as I will just have to crop them myself. I also do not want scans with the tops of buildings cropped off, clients often want to do cut outs or extend areas of sky to put type over. If the top of a spire or corner of a gable is cropped off they can’t do this. Digitisation also gives you the option to remove the lamp post that intrudes into the top left of your picture or the fag ends and crisp packets that have been discarded in the road. However, if your retouching is obvious to me then I will reject the scan. The most common errors are repeating areas where you have cloned a pattern, in clouds for instance, and the retouched area being a different texture to the surrounding area. These may not be obvious when the picture is reproduced, but if I can see them then I will not use them!
You should aim at producing a scan of roughly 52mb. Not all scanner software is that helpful where specifying output size is concerned so I am not that fussed what the eventual size is and it does not matter if all your scans are different sizes!
You will need to get your scanner cleaned periodically. Over time the mirrors and lenses in scanners acquire a fine layer of dust which results in softening of the image and light bleeding at contrasting areas in the picture. You may be able to clean them yourself, but this is not recommended by the manufacturers and may be quite fiddly, even if you can open the box the optics may still be hidden away. Mirrors will have an unprotected silvered surface which will scratch very easily so if you do try and do it yourself be very careful.
