How would you correct the problem if artifacts are in the microscope field?

I'm no expert in optics, but I'd expect that it depends on the particular artifact, and probably involves mucking about with the lenses. I'd think that you'd be more successful in getting a useful answer if you (a) were more specific with your question, and (b) try the biologsts... they spend much more time with microscopes than 99.99% of us chemists.