Autofocus issue with Sigma 10-20mm? Help!

Started 7 months ago | Discussions thread
jkjond
Veteran MemberPosts: 6,626
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Re: Autofocus issue with Sigma 10-20mm? Help!
In reply to banflu, 7 months ago

banflu wrote:

Hi everyone,

Been lurking for a while but finally registered here as I ran into a problem!

I bought a Nikon D5100 a few months ago (my first DSLR) and after a while I noticed that I really started to like wide angle photos so I also bought a Sigma 10-20mm f3.5 lens. From the start I had a feeling that it's autofocus wasn't 100%, but at first I thought nothing of it - I am only a beginner after all.

But recently I was on holiday so I used the camera (and this Sigma lens) quite a lot .. and I've had quite a number of out-of-focus photos. I later realised that they are never out-of-focus if I use live view. Of course, live view is much slower so it is quite an issue.

Anyway, after making extensive testing I came to the conclusion that the Sigma lens is to blame. Please take a look at this video: http://www.youtube.com/watch?v=zOeoLUQrp_A

In this test I placed the camera on a small tripod (gorilla pod) and attached a focus test chart on the wall. I focused on the chart multiple times using live view. It always focussed perfectly - any photo i take in live view is 100% in focus. Later I put it out of live view, and the focus setting is visibly different in the focus window on the lens. Also, the focussing is inconsistent when not in live view. Put it back to live view and it becomes 100% consistent and perfect.

I later tried this same test with a Nikkor prime 50mm lens, and it worked perfect - the focus is always exactly the same, both in live view and in normal view.

Any thoughts? Has anyone else had a similar issue? The lens is still under warranty ... should I try to get a replacement, or should I fork out more $$$ and get a Nikkor 10-24mm?

Many thanks in advance for your help!

Interesting to see your video. I'm not sure what I can learn from it as there's no support information. One important aspect is where the focus point is set, or are you using a pattern array for the camera to decide? Posting sample images may have been helpful.

I have a 10-20 and found it very sharp, and as your 50mm is performing fine I'd suspect you have a duff copy of the siggy. With WA the DOF is usually large especially on DX, so focus issues are rarely a problem. Lenses and bodies have an accepted tolerance when it comes to focus - your body may be at one extreme and the WA at the other, yet your prime could well be just as far out as your WA but a better match for your body.

I'd look into the warranty.

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Wedding and fine art photographer based in the Lake District, UK

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