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  1. #1
    Join Date
    Feb 2006
    Des Plaines, IL

    Question Naked or filtered ... which works better

    I have performed this test with the CZ 135mm f/1.8 ... and found its autofocus deeply affected, close-up, on the wide aperture. Using Manual Focus, the UV-filter had no effect. I was able to achieve a sharp, accurate center-of-focus (or spot-focus) on my subject.

    The autofocus center-of-focus (f/2.5) shifted 1-3mm further back, directly caused by the addition of a relatively decent UV-filter. That can be a tremendous mis-focus, when you are going for sharpness and especially with a lens you paid over a grand for. Like I previously mentioned, manually focused, with the UV-filter on, I was able to get a sharp focus at the COF. Immediately switching back to AF ... it drifted back off to the 3mm displacement.

    Solution: Obviously, shoot NAKED! Yep, remove the filter when you are ready to shoot with AF ... and your focus should be right on the mark. Mine has shifted to precisely where it should be.

    The reason for this test was because it was suggested to me that I should try using my CZ 135mm f/1.8 in my remote bird shots. Well, as you can imagine, protecting the lens from damage is an important aspect of such an effort. The animals certainly have no respect for the costs involved and having squirrels crawling all over the equipment is to be expected. The weather, too, plays a major role, as we are having rain and wind storms every other day. Using a UV-filter in a prophylactic role seems only prudent ... but, it is screwing up the focus to such a degree, the 135mm is not performing any better than 70-300mm f/4-5.6 on a bad day. I would have gained nothing by risking it.

    But, as risky as it is, the reality of it is far worse. If I want to enjoy the power of this lens ... to hell with the filters.

    Just thought I'd share, just in case you wonder what happens shooting through UV-filters. I have personally found that lower-end lenses seem to be more tolerant of the UV-filters. The cheaper the lens, the cheaper the UV can be. Or ... the more expensive the lens ... the less protection you can provide it. Although, there is a limit to that, also. It is like having an extremely sharp scalpel ... it does not take much to dull its edge. If it is a butter-knife, who cares?

    Many will argue that putting a $50 filter on a $75 lens is silly. I would tend to agree and that's why you should probably lift your sights a little higher in your expectations. You really should assume that you are probably going to get a better lens, eventually. Within that line of thinking, already having a good UV or polarizer should be a consideration. If you spend less than $70 for a polarizer-filter (CP), then you have probably goofed up your autofocus to some degree when using it.

    Best way to check is to shoot the length of a yard stick, meter stick or tape measure.
    1. Place your focal target (something 3-D, not flat) along it at some point just past the Minimum Focus Distance (M.F.D.) of your lens. {if your M.F.D. is longer than 3-feet ... just move the yard stick with your focal target, so that you can see the graduations in front and after the focal target}
    2. Take an image (preferably on a tripod) w/o the filter
    3. Without changing the settings or distance, add the filter, refocus and reshoot

    At this point, you should be able to see the difference in image. Heck, shoot it a couple times (w & w/o filter), to repeat results and confirm. It should really open your eyes as to the image quality and impact your UV or CP filter is having on your photography.
    Last edited by DonSchap; 04-02-2009 at 02:32 PM.
    Don Schap - BFA, Digital Photography
    A Photographer Is Forever
    Look, I did not create the optical laws of the Universe ... I simply learned to deal with them.
    Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.

    flickr & Sdi

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