I've always worried about scratching the glass/lenses of my optics so I generally use my air compressor to produce a shot of high pressure air to blow off any dust and debris, then wipe lightly with a dry cotton ball, then getting another clean one and rubbing my firmly. However, i don't really know if there are better techniques and/or chemicals like rubbing alcohol that I should be using. Also, what about cleaning in the field if out on a long day of birding? thx for the input