Using film scanners

When I use Silverfast, which I don't here, I've always just set it to scan for my preferred print size and let it choose its own resolution. I don't recall any magnification -- can you show us a screen grab of the dialogue?

Magnification was the wrong word - the software refers to 'scale'. I've will post screen grabs to show what I mean.

OK. What it's saying is: "How much bigger than your input do you want your output to be?"

In your example you have an input scan size of 6"x4" to work out how it's going to scan it, SF is asking what your intended print size is. This is probably irrelevant to you. However, if you were scanning a negative of, let's say 2.25"x2.25" and wanted to print it at 16"x12" you could enter the 16" or the 12" in the width or height box and SF will calculate the height or width and the scale factor. Or you could enter the scale factor and have it work out the width and height (see how they're all 'chained together' on the screen?)

So, the scale is not really terribly useful unless you particularly know that you want scan something and print it out X times bigger. e.g. if you were scanning something A6 to print A4, you could enter 400% for the scale.

N'est-ce pas?

[edited for arithmetic]

I can see that, however I'm not sure why scanning at 800 ppi with a scale of 200% gives a different file size to scanning at 1600ppi and scale 100. Clearly something is going on in the software and I'm not sure what the image quality implications are going to be - other than assuming that the bigger file is the better option, which of course may not be the case if the additional data is added by interpolation.

'scale' makes no difference to the scan contents -- it's just a confusion/convenience in the user interface that's supposed to free you from worrying about what resolution the scanner scans at.

Your files are different sizes because one is at 800 ppi and one is at 1600 ppi

I'm obviously missing something here, because I can't see how two scans, one at 800 and one at 1600, can give the same size print without some loss of quality - at least at the largest size possible.

They don't give the same size file (the print size depends entirely how you print them!?).

If you're scanning a 6"x6" original (just so I don't fsck the arithmetic) then at 800 ppi you'll get a file 4800x4800 pixels, at 1600 ppi it will be 9600x9600

If you then printed the two at 300 dpi you'd get prints of 16"x16" and 32"x32"

I feel like I'm teaching you ovum/vacuum techniques here and not really understanding your question.

Here's how I use Silverfast, maybe this will break the cognition barrier.

I stick my neg in the scanner and do the preview. SF then tells me how big the neg is. Ignoring the 'scale' and resolution I just tell it what my intended maximum print size is, e.g. for 35 mm I will tell it to scan for 16"x12" @ 300 dpi

Then I hit the 'scan' button. I still don't look at, or care, what 'scale' or 'ppi' are set to. I trust SF to drive the scanner at its optimum. Then I take the TIFFs home and get to work on them in Photoshop.