I haven't had the time to do some more scanning and check what happens, but Vuescan is pretty good at only offering features when the hardware is capable of them, so I'd expect that if the option is there, then the scanner can do it.
Mind you, Vuescan has three similar-sounding options, which aren't actually the same. In the Input menu:
"Number of samples" - this asks the scanner to record multiple readings at each point, and then averages them. Not all hardware can do this.
"Number of passes" - this just makes multiple complete scans, and averages them. All hardware can do this, but it relies on the mechanism putting the film/CCD in the same place every time it reads a particular location.
(For both of these, you need to do a lot of additional samples/passes to get significantly better signal-to-noise - four samples should double the S/N, nine samples ought to give you three times the S/N etc... If you have a lot of visible noise, then this might not help as much as you'd hope!)
"Multi exposure" - this is the one you were referring to Kev, where Vuescan asks the scanner to make two readings at each point, the second with the exposure increased to get into the shadow detail. Now I think about it, I'm not sure that I've tried this, or that my scanner can do it.
I've also not yet tried scanning slides - just B&W negatives. Vuescan only offers the film-type presets appropriate for the type of material that you've told it you're scanning, so there might not be very many for slides. However, I concluded from emails from the author that all the film-types actually do is fiddle with the "fog+base" offset (which I assume is the black or white-point as appropriate) and the "gamma" which is the brightness control.
Of course, you will always get worse S/N in the darkest parts of the image you are scanning - in negatives this will end up in the highlights where it probably won't be as noticeable as for positives, where the most obvious noise will end up in the shadows. It ought to be possible to improve this a bit by making sure that the exposure used by Vuescan puts the shadows a bit further up the scale, and then bringing them down by adjusting the black-point. You have got the menus in "Advanced Mode" haven't you? (This is selected by the "More" button at the bottom of the menu panel). I always use Advanced mode which, as well as giving you more options, displays a "Graph" at the bottom of the menu area. This can be toggled between views of the histogram of the raw scan (which shows how well the exposure has spread the available signal over the range from 0-255) a view of any curves correction you're applying, and the output histogram. I find it very useful to flip through all these as I'm working, as it gives me a good idea of how good the data I'm getting off the film are, and how much manipulation is actually needed! If, for example, the raw histogram shows everything bunched down near zero, then you could select "Lock exposure" in the input Menu and manually increase the value before re-scanning.
This has gone on a bit, but I hope it helps!
Andrew
