Gunzorro
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 p.2 #17 · Thanks to those that commented on No Filter (UV or similar) on 100-400 | |
There are a lot of opinions on protective filters.
My opinion is that there is a good chance they degrade IQ slightly. I'm willing to be cautious and refrain from using them in situations that I completely control, with no unexpected elements or motions that could inflict damage to the front element. Or using lenses I don't care much about. 
Here are a few thoughts and experiences.
My first view camera (Kodak Korona) came with a lens (Kodak Anastigmat) that had a large gouge in the front element, and some less critical scratching. I was able to take pictures, but the lens was essentially worthless -- it was worth more for the shutter. No provision for a filter on this older lens, at least not a convenient size (probably like 39mm).
I bought a Nikon AIS 180/2.8 ED lens with gouged and deeply scratched front element. Someone had obviously had it in the camera bag loose with other Nikon lenses, and the lens cap came off (or was not put on). The metal "ears" for aperture control of other lenses obviously banged and scraped into that front element. Again, the lens was nearly worthless for resale, but I used a Sharpie to darken in these specific marks (the element was mostly clear and unscuffed), as the marks did cause noticeable flare if sun or bright light touched the surface. The bad news is the marks are visible to posed humans, and they leave telltale blemishes in the bokeh circles. A filter would have taken the beating, not the lens element.
I bought another used Nikon AIS lens, a 24/2, which had been obviously carried PJ-style -- in a bag without caps. The front glass was scratched and scraped all over, and the back element was essentially a special effects fog lens due to the rough-buff it had gotten all over. The mechanics were beaten to hell too. I sent to Nikon and got a rebuild and replace of the front elements section, but the rear could only be slightly polished. Cost me about $200 more for the repair, and now I have a lens that works pretty good from f/2.8 to 5.6, but looks fuzzy wide open or past 5.6. When I go to sell, it will be worth about $50, despite all the work, and would have been less if the front element was still marred. (Undamaged, the lens sells used for near $300 in excellent condition.)
I had bought a brand new Zeiss ZE 21/2.8, and when I went to sell it after about a year of ownership, I noticed a small scratch on the front element. I'd fallen under the sway of the "no filter" crowd, and apparently the metal lens hood had slipped once on mounting and scraped the surface. I could see the mark, and had to disclose it for sale, even though it didn't affect IQ in the least. That cost about $200 and make the lens much more difficult to sell -- people seem to think if you are honest, you are covering up even worse faults! 
I've bought lots of used lenses that have marks on the front glass, and if they weren't disclosed in the listing, I ask for a minor refund, or return the item. I've gotten a lot of good deals myself from this "damage" and the lenses are generally fine with no affect on IQ. But it is a crap-shoot, as with the severe damage that occasionally turns up. This complexity and uncertainty turns off a lot of people to buying used lenses or gear in general -- and that contributes to the affordable prices for those wishing to chance it.
From a cosmetic standpoint, I've had the metal ring of the filter come in contact with cement structures plenty of times while out photographing building, especially when setting the camera down for a minute or two. Otherwise, marks would have been left near the lens' filter ring, making marks on the front of the lens barrel. Naturally, I try to find soft things or take along my camera bag, but that isn't always possible.
Who's ever had camera with a front heavy lens drop forward on a tripod, slamming into the leg, leaving a little impression on the filter rim? Or the actual lens, if you didn't have a filter mounted? I prefer the filter rim being a tiny bit marked up, not the lens bent.
At events, and while gyrating around in landscape, in I've had plenty of contact and light frontal impacts on the filter mounted on a lens -- pens, nails, cuff links, branches, etc -- that leave permanent marks on the filter. These would have gone on the lens and at the least lowered its value and desirability. (Then there are salt spray, coffee spray/drops, pitch, etc, that may or may not mark, but are a bitch to remove.) Granted, for catastrophic damage, like dropping the lens on cement, or being hit with a hammer, the filter could do more damage than not -- then again there are instances here where the filter protected the filter ring and front element! But for minor impacts, I think it is prudent to think the filter will take the beating instead of the front element.
In checking and cleaning UV and CPL filters, I'm amazed at how much film and dirt gets on the lens in a few weeks or months of light use outdoors in city situations -- even more in the "wild". Upon examination, I find small scratches from things rubbing on the surface in "normal" use, plus a build up over years of ultra-fine cleaning marks. If people think these marks, films, and smudges don't affect IQ, I don't know that to say to convince them!
Going into inclement surroundings, I'll always consider my lenses as needing the filter to complete a safety seal, even for a non-L lens. Naturally, if I had a lens that I could confirm IQ degradation, I would leave a filter off except in the direst need.
I avoid filters as a calculated risk, when I can control the environment (about 70% of the time) -- then I think there is an advantage to IQ, at least temporarily while the lens is clean. So, I'm firmly in the middle of the discussion. I try to use a lens hood with no filter along, but it's not always practical.
Whew! Word, up! 
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