There are a number of techniques for transferring an image from 35mm film to 35mm film. These include contact printing, using an enlarger, using a camera, or re-photographing a print. Probably the simplest is to use a camera. You need a "slide copyer", which holds film or slides in place, in front of a piece of opal glass. A macro lens and bellows, or similar, and an SLR. You can then crop the picture as you go.(posted 9545 days ago)The biggest dust problem is liable to be on the original film. I use a camel-hair brush and a loupe. Brush the film, then use the loupe to examine the neg against the light. Also orient the neg to get light bouncing off the surface (so the surface looks white); this will show up other dust. Then brush off each bit of dust. This only take a couple of minutes per negative, but a quick ten-second brush isn't enough.
Each neg must be brushed just before photographing it.
A normally exposed and developed negative of a normal scene will give a density range (on B&W film) of about 2.0, which corresponds to about 7 stops. By a nice coincidence, this is about the same as a "normal" scene, so it should photograph nicely. However, if the original neg has a wider range of tones, you should reduce the contrast of the copying film (basically, over-expose and under-develop). Conversly, a thinner original will need an increased contrast for the copy film (under-expose and over-develop), but this is less likely.
If you were copying colour slide film with colour slide film, you would have to use other tricks to control contrast. But with B&W film, you can readily control it with development.
I've never needed to photograph colour negative film. I suspect this is inherently lower contrast than B&W film, in which case you would have to increase the contrast of the copy film.