@ebiggs1 wrote:Some people say that a Protective, or UV, filter reduces the quality of an image. They are referring to an extremely high level of quality that is not required by most people on this planet. If you want to ensure that your image quality does not deteriorate, get a good quality filter and keep it clean. And in that instance where the filter may introduce 'flare' or 'ghosting' simply take it off. How many of you forget, you can remove the filter just like the lens cap! It does not become one with the lens.
I have seen what I consider very signficiant loss of image quality due to filters... not just minor effects. A lot depends upon the quality of the filter. But any added optics in front of a lens is going to have some effect. Maybe a little. Maybe a lot. It's a range of types of effect: ghost flare, veiling flare, tints, uneven effects, image softening, focus errors, "crazy" bokeh, increased chromatic aberrations and more.
As a rule, better quality, multi-coated filters under ideal conditions minimize loss with most lenses.
But some lenses really don't play well with filters (the EF100-400L is an example).
And who knows when I'll find myself shooting into the light and seriously challenging my lens to get a good shot.
I paid good money for high quality optics to make good images... I'm not going to mindlessly compromise every single shot I make with that investment by sticking a filter on it 24/7/365 (even tho I can remove it, if I remember... and have time to do so) in hopes that a thin piece of fragile glass might someday protect my precious from an unknown danger.
To me that makes a great deal more sense to just leave the filter off the lens and only install it on those rather rare occasions where there actually are some risks to the lens (or when I want the effects of a polarizer... or want the effects of a neutral density filter... or any other type of filter).
This way, there's much less chance of forgetting to remove the filter and ruining an image. Or, if I do remember, to find myself still fumbling to remove the filter and stick it safely away in my bag, while a great shot opportunity passes me by.
IMO a quick and easy to remove clip-on lens cap does a far better job protecting the lens (as well as protecting the filter, if and when one is being used).
Here are some actual examples of what can happen in an image when a filter is used. I deliberately used a B+W MRC C-Pol on my Tokina AT-X 12-24mm f4 , to see what would happen in a strongly lit situation....
First, there were a number of ghost flares occured various places in the image (some do not show up at Internet resolutions, but are obvious at higher magnifications and in greater enlargement such as prints of the image)....
Both the lens and filter are high quality and resistant to flare, so these ghosts are fairly minimal and rather easily cloned out in Photoshop. Still, it's extra work that could have been avoided.
Worse was slight, general softening of the image that increased chromatic aberrations...
This was stronger toward the edges (above), as might be expected, but occured to some extent throughout the image...
CA is much harder, though still possible to correct to some degree.
There also was overall veiling flare that required boosting contrast and color saturation to correct. But the quality of the lens and filter was such that there weren't any ugly color tints (which I've seen filters cause in other strong lighting situations, and are a pain to correct when they occur only on part of the image).
The end result of the corrected image in a size and resolution for the Internet isn't too bad...
... but it would be hard to make a good print of any significant size from the image.
It's sooooo much easier to just not use a filter - except when one is really called for - and have minimal "corrective" work needed on the finished image...
Canon EF 20mm f2.8 was used on 5DII for the above, without any filter (shooting very quickly, handheld, because light was fading fast).
You also have to watch out for uneven filter effects. The veiling tint mentioned above is one example. Another is the way a C-Pol tends to have variable effect especially on wide lenses and depending upon where the sun is in the sky. For the image below, I deliberately used a C-Pol to darken the sky more behind the lighthouse...
Above was, once again, EF 20/2.8 lens on 5D Mark II, with B+W MRC C-Pol. The uneven sky was deliberate here, but might not be in other situations. There's a tiny bit of loss of fine detail due to the filter (even though it's another high quality, multi-coated B+W), but it's minimal here because the camera captures a lot of detail and the sun was well out of the image, off to the left of the camera. In this case, I felt it was worth the slight loss as a trade-off for the positive aspects of the filter's effect. In other cases I've had images I felt were ruined by the uneven effects of a C-Pol.
In addition to the cap, a lens hood also provides good physical protection for a lens. Especially with telephoto lenses, a nice deep hood will provide really good physical protection while shooting. And since the correct hood properly installed cannot possibly have negative effect on images, it's something I always recommend using... even when it's a little inconvenient (such as when using a filter that needs to be rotated, like a C-Pol).
When I first got an EF-S 10-22mm and saw how it's rather large hood was a pain to fit into my camera bag, I thought maybe I could just get by without it. After all, that hood is so shallow and that lens is one of the most flare resistant of all the ultrawides. So to answer my own question, I ran a quick test shooting the same scene with and without the hood (and no filter either)...
I think the results of this quick test sort of speak for themselves.
In the end, I'd simply suggest anyone who wants to do so go ahead and get the filter... But don't simply accept the recommendations from a sales person in a store or faceless individuals like me on Internet forums. Do some with and without comparison tests for yourself, so you know exactly how it's going to effect your images, then can decide whether or not it's worth it, and are prepared to deal with it in different situations. The above lens hood comparison convinced me, yeah, it's worth the extra effort of carrying around the rather large, matched hood for the EF-S 10-22mm. Do your own challenging lighting shots with and without the filter, to see how much work you need to do to correct for the problems the filter causes (if the image is even recoverable). Over three decades of shooting with all sorts of gear have convinced me that filters merely for purpose of "protection" are more often a problem than a solution, don't really reduce the risk very much anyway, and that my lenses are better off "naked" most of the time.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
