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01-02-2012, 11:22 AM   #1
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IQ degraded due to Filter..??

I've tended to be a UV filter addict from the old school of protect the lens thought. But was playing with my Sigma 170-500 on the new K-5 a bit over a month ago, and while doodling thought of comparing images with and without the UV filter.

I tried to keep things the same as best possible, although focus points might not be perfectly the same, and the results seem to show an appreciate IQ degradation with the filter on. I did a few repeats on roof tiles and paving bricks with similar results, but the image of the aerial bracket seems to show best what looks to me like a fine-fine mist over all the images with the filter on. The sand grain detail on tiles and cracks on black insulation of the solar heater on the second series are also distictive. This was shot something like anti-clockwise starting top left.

Anyone else done tests with positive degrading results? Filter was Kenko UV Japan

Should I be thinking of binning or selling off these UV front element protectors.

Typically around 500mm 1/500s f/13 iso200




01-02-2012, 11:28 AM   #2
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If it's a low-quality filter I wouldn't be surprised to see a degradation this severe, however, when using modern filters (i.e. Hoya UV filters) there shouldn't be a noticeable difference.

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01-02-2012, 11:41 AM   #3
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There has been some discussion on eBay of counterfeit Kenko UV Japan filters being sold. They're lower cost filters to begin with but still people copy and counterfeit.

There are some excellent resources out there that compare the quality of the filters and how they impact the IQ of the images. Oddly, at least to me, while some brands were consistently rated high that was the exception with most having models that came in at the top, middle, and bottom from the same brand. I know that Hoya, for instance, has some solid performers and some real dogs among their filters based on many reviews I have seen.

Here is an excellent review of 24 different UV filter models:
UV filters test - Introduction - Lenstip.com

For example, Hoya has lenses at the top and bottom but has 3 models at the top:
Hoya 72 mm HMC
Hoya 72 mm Pro1 Digital MC
Hoya 72 mm HMC Super

But the HMC model is the least expensive among those three and rates essentially the same as the #2 which was literally twice the cost. But the Hoya 72 mm UV-0 - Standard model, which costs the same as the HMC model, rated rather poorly overall. So, maker is NOT the main factor and its important to read some independent reviews in my experience. They led me to a filter maker that I was unfamiliar with, Marumi, for my 10-24mm lens based on performance vs. cost and I have been very happy with its performance.

Last edited by Docrwm; 01-02-2012 at 11:57 AM.
01-02-2012, 12:02 PM   #4
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Some lenses really hate filters, don't know if the Sigma is one of them but might well be.
Don't know if anyone does use this lens with filter without a problem?

01-02-2012, 12:06 PM   #5
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QuoteOriginally posted by Anvh Quote
Some lenses really hate filters, don't know if the Sigma is one of them but might well be.
Don't know if anyone does use this lens with filter without a problem?
Certainly you could be right about the lens not doing well with any filter, but I can't imagine that a poor filter isn't worse than a good filter in its impact on the IQ. Personally, I use only ND or Polarizing filters on my lenses and hoods on all of them. The LensTip.Com review of C-PL filters is a good place to start reviewing them:

http://www.lenstip.com/115.4-article-Polarizing_filters_test_Results_and_summary.html
and the supplement to that review
http://www.lenstip.com/119.1-article-Polarizing_filters_test_-_supplement.html
01-02-2012, 12:11 PM   #6
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The greater the lens focal length the greater the focus shift with a filter of non-zero thickness. This can be offset by refocusing with the filter in place--try this before deciding it is other degradation due to filter. (BTW this is one reason the Wratten (kodak, now I believe Tiffen) gels were (are) used--they are thin.
01-02-2012, 12:19 PM   #7
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QuoteOriginally posted by dms Quote
The greater the lens focal length the greater the focus shift with a filter of non-zero thickness. This can be offset by refocusing with the filter in place--try this before deciding it is other degradation due to filter. (BTW this is one reason the Wratten (kodak, now I believe Tiffen) gels were (are) used--they are thin.
Interesting.
However you say it use even thinner glass so how much is it then still worth as protection, certainly for such a larger filter size...
01-02-2012, 12:39 PM   #8
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QuoteOriginally posted by Adam Quote
If it's a low-quality filter I wouldn't be surprised to see a degradation this severe, however, when using modern filters (i.e. Hoya UV filters) there shouldn't be a noticeable difference.
Agreed... I use Hoya's and they produce no noticeable degredation of IQ...

01-02-2012, 12:44 PM   #9
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If a filter is made very well (very flat, even thickness, and mounted perpendicular to lens), doing the refocusing is fine--and there is little/no degradation (except for flare)--and giving lens protection. But if less than perfect--then one way to address problem is make it thin (which means not of glass, etc.)--but yes that means it does not protect the lens. But lens protection (and increased color saturation) is also obtained by using a good (metal) hood (although not the same protection--particularly for glancing blow that may knock hood off).
01-02-2012, 12:47 PM   #10
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QuoteOriginally posted by DaveHolmes Quote
Agreed... I use Hoya's and they produce no noticeable degredation of IQ...
Does every filter degrade the IQ? I have a B&W Haze filter on my 50 1.4 (came with the lens and decided to leave it on). I also have a UV filter on my 55-300 (can't remember the brand right now). I've always wondered if I should leave them on, or take them off.

I know a lot of people are completely against using filters. I don't really use those filters for the effect, I leave them on to protect the lens. Is this really necessary?
01-02-2012, 12:53 PM   #11
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As regards hoods--on second thought-I guess the glass filter being broken--absorbs some shock--so if the lens smacks a rock/pavement head on the glass filter will be much better.

Why not try and see if the shift problem is there--and if not then try another approach. Maybe by a high quality used filter (can be any type) and see if it works--a filter type not used for digital and thus low $ now (or borrow from a friend)--if it works (no degradation) then invest in the particular filter you require.
01-02-2012, 12:55 PM   #12
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Please read the reviews I linked to because assertions like "Hoya filters...." are just not supported by the data. Its NOT a particular brand but specific models. Some brands do better overall but most have dogs in their lineup, including Hoya specifically.

Last edited by Docrwm; 02-27-2012 at 05:49 AM.
01-02-2012, 01:04 PM   #13
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QuoteOriginally posted by Docrwm Quote
Please read the reviews I liked to because assertions like "Hoya filters...." are just not supported by the data. Its NOT a particular brand but specific models. Some brands do better overall but most have dogs in their lineup, including Hoya specifically
This I suppose has some merit... All my UVs have come from the same store... Guy stocks 3 variants of Hoya UVs in various filter-ring sizes... I buy the ones that are priced in the middle... eg for my FA50 (49mm) I paid 35(ish) not 19 or 60... Same model on my Tamron 17-50 (67mm) was 50(ish) not 30(ish) or 100(ish)...

But this is the same for all filter types too... I have a Hoya 49mm CPL which is very good and a 49mm Hama CPL which is complete dross...
01-02-2012, 01:10 PM   #14
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Re-looking at your first two images--it does look like all planes are better IQ--so although my comment about refocusing is still theoretically sound, and possibly an improvement, it does appear the filter caused some loss of sharpness. But try it again with refocusing (maybe even vary the focus point slightly over several shots) before spending $. Ultimately If a better filter is required I would think you are looking at a few hundred dollars--at which point the extra protection may not cost effective.
01-02-2012, 01:21 PM   #15
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QuoteOriginally posted by DaveHolmes Quote
This I suppose has some merit... All my UVs have come from the same store... Guy stocks 3 variants of Hoya UVs in various filter-ring sizes... I buy the ones that are priced in the middle... eg for my FA50 (49mm) I paid 35(ish) not 19 or 60... Same model on my Tamron 17-50 (67mm) was 50(ish) not 30(ish) or 100(ish)...

But this is the same for all filter types too... I have a Hoya 49mm CPL which is very good and a 49mm Hama CPL which is complete dross...
That's why I really value the tech guys and their attention to detail in analyzing 25+ filters with some standardized measures, most of which are objective, for things like light transmission and wavelength distortion and such. My examples were chosen because they involved the same company but different models and the fact that the highest priced models were not the best optically.
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