The photographer Kurt Munger ran an experiment on how much dust, scratches and damages of the lens affect image quality. Â The results are very counterintuitive. Â At least for me. Â Fingerprints, dust, scratches, and even bits of non-transparent duct tape have no effect what-so-ever. Â The first signs of something going wrong appear with very serious lens damage, like this:
Even then, the image is not as bad as you’d expect. Â Here it is.
Read the whole thing for more details.