How much dirty lens affects image quality

The photographer Kurt Munger ran an experiment on how much dust, scratches and damages of the lens affect image quality.  The results are very counterintuitive.  At least for me.  Fingerprints, dust, scratches, and even bits of non-transparent duct tape have no effect what-so-ever.  The first signs of something going wrong appear with very serious lens damage, like this:

broken lens

Even then, the image is not as bad as you’d expect.  Here it is.


Read the whole thing for more details.