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12-31-2010, 01:27 PM   #1
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UV Filter on Sigma 10-20mm Lens

I recently bought a Sigma 10-20mm f4-5.6 EX DC lens. I've always covered my lenses with a UV filter because I shoot primarily outdoors in all weathers. The only wide angle lens I have owned was a Zuiko 28mm for my Olympus film camera, which isn't very wide, so I'm new to this type of lens.

The Sigma lens element bulges quite a lot, and I'm concerned that a UV filter (regular, not thin) I bought for it might touch the lens element, so I have been nervous about mounting it. When I asked the technical helpline at B&H if the lens element would contact the filter glass, I was told that the only difference between the regular filter and the thin was that the latter does not have threads on the outer side of the rim to avoid vignetting. Because I'm not concerned about vignetting, and use the UV for protection and also like to use the lens cap when the lens isn't in use, I bought the regular filter.

I've tentatively screwed on the UV to see if I could tell if there's contact, using a hand lens to check. I THOUGHT I saw a tiny disk of contact but can't be sure.

Am I being overly concerned about this? Do others use a regular UV on this lens without problems? And how can I be sure if there's contact (or not)? It's awfully hard to tell.

I know some folks prefer to leave the lens exposed for better IQ, but I often slide my camera (and whatever lens is mounted) inside the front of my jacket when on a shoot to protect it from cold, knocks, and precipitation, so feel more at ease if the lens element itself is isolated from scrapes and crud.

12-31-2010, 04:39 PM   #2
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FWIW, this happened to me when using a 24mm lens with a fisheye adapter, the lenses touched.

I ended up using a step up ring on the 24mm and a step down ring on the adapter. If you're really worried, you could get a step up ring and a larger UV filter... I'm just not sure how that would work out on the 10 side of your zoom...
12-31-2010, 05:07 PM   #3
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Never had a problem with the UV filter than came with my Sigma from Adorama (Tiffen 77mm thin UV).
12-31-2010, 05:31 PM   #4
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I didn't have a problem with the UV filter that came with my 10-20 either.

If you are concerned about it, why don't you try what the Dentists use to determine contact. Take a piece of carbon paper and place between the lens and the filter with the carbon facing the filter. Thread the filter gently down until it seems to stop, mark that position on the side of the filter, unthread and see if there is a carbon spot on the filter surface. Do it again until you get no further progress on threading the filter in. regular paper is .004" thick. If the carbon doesn't touch the filter under this procedure, then you are guaranteed at least that much gap.

(i'm just thinking this up as i go along - try it at your own risk :-))

best wishes and congrats on the lens, i really like mine.

12-31-2010, 05:44 PM   #5
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I use a Marumi CPL filter with no problems.
01-02-2011, 08:51 AM   #6
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Thanks everyone for your comments and suggestions. I decided to play it safe and devise a way to block the filter from screwing on as far as its and the lens' threads would allow. I did try to keep it on backed off, but the filter was loose enough that way that I was concerned I might just pull it off one day (that happened to me a long time ago with a polarizing filter).

Here's what I did: I took a length of black (could use any color, but that's what I had) heavy-duty sewing thread, and tied a square knot from one end around the thread to make a loop. I placed this over the filter into the groove of the screw thread closest to the filter glass. Gently pulled the knot along the sewing thread until it tightened into the groove. Cut off the tag end. I then repeated the process, placing a second loop of sewing thread over the first.

Tested the filter on the Sigma lens. The filter screws on only about two turns instead of the three or more. The sewing thread offers a bit of a hold on the filter and also helps prevent the filter from tightening down so much it threatens bringing the lens element and filter glass into contact.
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