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11-26-2010, 06:04 PM - 1 Like   #1
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Impact of a cheap UV filter

I thought I'd present a the result of a simple experiment to everyone here at PentaxForums. Enjoy.

BACKGROUND

I wanted to test what impact a UV filter would have on the resolution of a lens. When I first got my DSLR I of course got a UV filter to "protect" the lens and because the helpful sales person said I'd be crazy not to.

However I've now gotten three lenses where the hoods are solid enough and deep enough that I feel the lens is protected and I started to wonder what kind of damage the filter is doing.

I've got a DA 12-24mm f4 and it has had an Optex 77mm A1 filter on it since I got it off another forum member.

Henry's has this 77mm filter for $39, and as all Canadians know Henry's is almost always the most expensive place in Canada. So that can give you some kind of idea about the filter. For price comparison the very basic B+W UV filter is $118.

METHODOLOGY

The experiment consisted of shooting ten images with the filter on and ten with the filter off. The camera was locked down to a heavy tripod and the ballhead was secured.

The camera was set to x-sync and f8 and ISO 100, and tripped with a remote. Shake reduction was of course off. I even cleaned the filter with lens paper and before the test.

Lighting was a single strobe bounded into a silver umbrella mounted above and behind the camera.

Its freezing rain/snowing outside so I shot the fireplace, the only brick wall I have inside.

I shot RAW and created an action to load each image into photoshop and crop the centre. The automated action ensured that the conversion was the same for each image.

I then reviewed the series of 10 and chose the sharpest image for each set.

RESULTS

The image on the left is with the filter the one on the right without.

To say the least I was surprised how much of the difference there is, but I will let the results speak for themselves. (but I think I am looking for a new filter)

PART II

I repeated the test this morning with a Sigma 17-70mm Macro and a HOYA HMC Super UV(0) filter. The results are below in the attached image.

As expected (or at least hoped for) there is alot less change between images.

Attached Images
   

Last edited by omega leader; 11-27-2010 at 07:05 AM.
11-26-2010, 06:07 PM   #2
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Quite a difference.
11-26-2010, 06:09 PM   #3
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Not to say the image on the left isn't sharp. It is, just not as sharp.
11-26-2010, 06:15 PM   #4
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It appears to be more of a contrast issue, rather than sharpness, but still a better image without than with.

11-26-2010, 06:48 PM   #5
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I noticed similar results on many of my shots after removing a cheap UV filter. While I never did a brick wall experiment like this, my results were noticeable immediately. I was using a Sigma 70-300 and while it isn't known as being a razor sharp lens of the quality or the DA 12-24, my results were horrible. The filter came as part of the lens deal along with an equally cheap CPL and I put the UV on the lens out of old habit. I no longer use one at all. My Sigma was like a new lens.
11-26-2010, 07:04 PM   #6
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QuoteOriginally posted by Parallax Quote
It appears to be more of a contrast issue, rather than sharpness, but still a better image without than with.
??? I see a sharper image on the right regardless of contrast difference.
11-26-2010, 07:13 PM   #7
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I noticed the same thing a few years ago and generally shoot without a UV/Skylight filter.


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11-26-2010, 07:51 PM   #8
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Interesting post.
I was reading through another thread about the benefits of a UV filter...
I always had one on, if only for protection...

11-26-2010, 07:54 PM   #9
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QuoteOriginally posted by omega leader Quote
I wanted to test what impact a UV filter would have on the resolution of a lens. ...................(but I think I am looking for a new filter)
I had not seen this kind of test but there are lots more issues with filters, particularly the low quality versions. Check out the UV and CPL tests here if you want to see how much difference there is between the good, the bad and the ugly. The most expensive are NOT the least intrusive.

Articles - Lenstip.com

BTW, I routinely use protection/UV filters because cleaning salt water mist off a $1,300 lens is too painful.
11-26-2010, 08:12 PM   #10
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I should test this with my Marumi filters. I feel paranoid when I don't have a filter protecting my lens.
11-26-2010, 08:12 PM   #11
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Now you know why I let my lenses take their chances.
11-26-2010, 08:42 PM   #12
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QuoteOriginally posted by imtheguy Quote
Check out the UV and CPL tests here if you want to see how much difference there is between the good, the bad and the ugly. The most expensive are NOT the least intrusive.

Articles - Lenstip.com

It was the LensTip articles that got me thinking in the first place

I'm have a Hoya Super on my 17-70mm and I may redo this test with that filter this weekend.
11-27-2010, 12:44 AM   #13
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QuoteOriginally posted by Skullsroad Quote
I should test this with my Marumi filters. I feel paranoid when I don't have a filter protecting my lens.
Yes, me too, it's a bit like driving without a seat belt (which I don't do, of course!).

My main concern with filters was flare, but I can see I'm going to have to do a few tests for loss of sharpness...
11-27-2010, 01:44 AM   #14
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looking forward seeing a Marumi filter test, too. cause those i got))


as for omega leader test, that's quite a difference for me on those pictures! (but i just can't take off my UV filters from the lens... it's scary, to say the least!)
11-27-2010, 04:14 AM   #15
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This test proves that there is no point using cheap filters.

Good filters are a different story - you can actually see the difference between a cheap UV filter and something like a Hoya Super HMC UV filter in the way they reflect light. The former generally shows distinct reflections as you'd expect from a piece of glass, whereas the latter looks like a metal ring with no glass in it.
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