Sigma 17-70 autofocus problems with 550D

Esinem · Aug 31, 2014

A little history first before I get to the problem: I have just got my 550D back from Fixation after checking the 18-55mm kit lens and body for autofocus problems. It looks like I knackered the kit lens by forgetting to switch to manual before engaging follow focus *blush* on my rig. They also did some work on the AF and cleaned the camera. All now works great with my 1.8mm 50mm Canon lens, even in bad light.

I recently bought a barely used 2nd hand Sigma 17-70 (private sale, sold as seen). Autofocus seems erratic, especially under 1 metre. It will hunt for ages, often clearly by-passing the focus point, and then quite often settle totally out of focus. It seems much the same in LiveView and thru the v/f regardless of focal length.

Has anyone else seen this behaviour or know what's up? Could it be a question of some inexpensive recalibration or is it more serious?

I'm guessing I bought a lemon so need to run it into Fixation for a nice fate repair bill but good news is always welcome :-(

photonius · Sep 2, 2014

Esinem said:
A little history first before I get to the problem: I have just got my 550D back from Fixation after checking the 18-55mm kit lens and body for autofocus problems. It looks like I knackered the kit lens by forgetting to switch to manual before engaging follow focus *blush* on my rig. They also did some work on the AF and cleaned the camera. All now works great with my 1.8mm 50mm Canon lens, even in bad light.

I recently bought a barely used 2nd hand Sigma 17-70 (private sale, sold as seen). Autofocus seems erratic, especially under 1 metre. It will hunt for ages, often clearly by-passing the focus point, and then quite often settle totally out of focus. It seems much the same in LiveView and thru the v/f regardless of focal length.

Has anyone else seen this behaviour or know what's up? Could it be a question of some inexpensive recalibration or is it more serious?

I'm guessing I bought a lemon so need to run it into Fixation for a nice fate repair bill but good news is always welcome :-(

not sure if anything is wrong or if there is anything to fix. I have a 17-70 (the older non OS). It often did take a bit to focus at close focus distances. At close focus, hand shake is more prominent (as with tele lenses), and combined with slow focusing of the lens, it may not be easy to maintain the focus point stable enough for the camera to lock on. Now I use the 18-55 IS on my 550D, haven't use the 17-70 for a long time.

You could test the hypothesis by using it on a tripod and see if it works better.

karl mohr · Sep 2, 2014

Sorry to hear about your problems with the 17-70. I have one that I keep on my T3i 99% of the time. It has turned out to be a pretty nice lens and hardly ever misses focus.

Maybe you could take the lens to a camera shop and see if you can have someone there put it on a Canon body and evaluate its effectiveness.

Esinem · Sep 5, 2014

photonius said:
You could test the hypothesis by using it on a tripod and see if it works better.

--

Thanks guys. Well, I think I have my answer. Tried the tripod test. Same. Tried on a friend's Canon. Same.

Noooo! So, my new lens needs to go into the repair shop. Just what I need after a dead kit lens, AF repairs to the the body and having to replace almost every bit of PC hardware :'-(

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Sigma 17-70 autofocus problems with 550D

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