This thread is timely, or at least my reading of it is. I needed a fingerprint/scratch/dirt filter for the 300mm f/4.5 (circa 1981) I just picked up. A big sucker, 72mm. And by chance, while I as waiting at the Registry of Motor Vehicles to renew my driver's license I happened to find on my phone an article where some blogger had done a filter comparison. Back when I was shooting slide film in a prior life I wouldn't have believed a UV filter made much difference. But this blogger posted pics illustrating his observations. Assuming he hadn't doctored the pics to make a point, I could see the effects he described. Yeah, a supposedly neutral filter could make a difference.
So when I finally got to my favorite camera store and asked, the guy (same guy who sold me the camera few months ago) strongly recommended the Nisi Armor FX. Not cheap! But compared to the price of any decent lens it's cheap insurance. My older lenses have Hoya filters. Do they affect the images? I have no idea but under some situations it's possible. One actually came unscrewed and escaped on a trail some months ago. Fortunately I found it before I accidentally poked my finger into the lens, and it was unharmed. Would any pics have been better without it? Would a different frame material have made it less likely to escape? I dunno'. But I'll gladly spend a few buck to protect a lens and avoid degrading any pic that lens could take without it.
