Needed to return to my scanner for an old slide last night (Nikon 4000ED). Well, I did my best, but the results were not good ... OK, I've got used to that clean digital look, but still, a good slide and a good scanner should produce decent results.
Anyway, after thinking about it and doing a little searching round the web, I realised it might just be dirty. Its 3 or 4 years old, and never been cleaned. So armed with the instructions at this site:
I decided to give it a go. Well, the mirror was filthy - not just a bit dusty, but a layer of dirt & grime - I don't know how it relected any light at all!
Just did a rescan, and the results are much more what I'd expect.
So, if you still use a scanner, maybe think about giving it a clean. Note that it does seem that Nikon scanners are more prone to "dirty mirror syndrome" than other makes.