A friend of mine told me he uses a coffee filter in front of the nozzle of canned air to keep the gunk from getting on his negs. I've never done it or seen him do it, though, so I dont know how well it works. I've never used canned air, so I dont know how forcefully the air comes out. Perhaps there's enough pressure to blow through the coffee filter and still blow off dust on the surface? Maybe there's thinner coffee filters? I've gotten to where I dont question some of the stuff he does

I've always used one of those blower brushes. they're good for getting the dust off lenses, too