Like a recent poster, I have a little backlog of rather thin (underdeveloped &/or underexposed) negatives which scan OK, but are nigh-on impossible for someone of my limited darkroom skills to print. They require such short exposure times that it's hard to be accurate and consistent with them, even stopped down to f/22 (which I know is not best practice). I'm not worried about managing contrast, I can experiment with that.

I'm presuming an ND filter will go some way to ameliorating this for me ?

If so, will "any old" ND filter for a camera do ? (I mean of decent quality and no covered in scratches of course )

and yes, I am learning to produce negatives of appropriate quality for enlarging now ...