Today I would like to compare 4000dpi vs 2000dpi scans. Tree shots are perfectly suited for sharpness comparisons. The shot was made by my friend Philipp with a Zeiss 50mm lens on Fuji Velvia 50 probably at EV 14, which is f/11 at 1/125s. It was shot hand-held. Its a beautiful subject in beautiful light. And the slight underexposure and vignetting helps to keep the attraction centered to the main subject. In 100% view the image is sharp, but not extremely sharp. It is a typical medium format sharpness. The image above shows the original scan rotated by 0.4 degrees and scaled to 5 percent. It was rotated in order to keep the black frame lines straight.
I used the original, non-rotated file and an image downsampled to 2000dpi (also not rotated) for the first comparison. I compared the original version at 100% and the downsampled file at a 200 % view and it was impossible to see a difference. I also did not see any difference between the 400 percent and 200 percent view.
Then I brought rotating into play. I rotated the original file and I rotated the downsampled file by the same amount. Then I enlarged both versions to 200 and 400 percent respectively and was finally able to see a difference (mouse over for the 2000 dpi version):
It is mainly the film grain which makes the first image appear sharper. No real details are lost but anyway the 2000dpi looks less sharp. Please consider that this is not a 100 % view but a 200 % and 400 % view. It is hard to see anything at 100 % here. I recommend 2000dpi scans when file size is critical and the shot is not extremely sharp from the beginning. You will still get top-quality compared to an image from a digital camera or a scan from 135 film. You will still get a good quality after rotating or other transforming but the quality of a transformed 4000dpi scan is clearly better - at least when you plan to make huge prints of it.