Originally posted by Marc Sabatella Ok, but let's put this in perspective - we're talking about sacrificing IQ for cosmetic reasons. The loss in quality from the filter is assuredly worse than the loss in quality from the potential scuff mark the filter is designed to prevent.
True, but in all practicality, I've done a few experiments with and without filters and never seen any image degradation from using a (quality) filter in all practicality. The only issue I noticed is a perhaps bit of extra lens flare with bright light sources in night shots.
I have bought and sold a lot of lenses and there is no doubt that front element damage reduces lens values markedly. Try convincing a potential buyer that a scratch, scuff, or 'cleaning mark' won't affect image quality or the value of a lens!