Sigma 120-400mm focussing issue

[98kellrs]

So I've had my Sigma APO 120-400mm f4.5-5.6 DG OS HSM for 6months now after purchasing it from an online vendor. I shoot mostly motorsport and it has been my firm favourite lens ever since I received it. The images were nice and crisp at all focal lengths and I was generally really happy with how well it focussed exactly where I needed it to.

I went away for a couple of weeks and when I tried to shoot some motorbike racing on the weekend I had incredible difficulty getting a sharp focus on any of the bikes whilst panning. At first I thought I was just rusty and persevered with it, but to no avail. Eventually I tested on a stationary subject and this is the result:

http://i6.photobucket.com/albums/y203/98kellrs/Sigma-1.jpg

Crop of above image:
http://i6.photobucket.com/albums/y203/98kellrs/Sigma-2.jpg

This image was taken at 400mm, f5.6, 1/500, ISO 100 using the central focus point in AF mode. I've had a look at both ends of the lens and it doesn't appear to be an issue with dirt on the lens. I've tested my 24-70L which seems to be fine so I'm pretty sure it's a problem with the lens itself.

Does anyone have any suggestions as to what tests I could run to isolate the problem? Or should I just send it back and get it fixed? It looks like it's front-focussing to me, but I have no idea what could have caused it to do that so suddenly! (I treat all my gear like it's made of crystal)

I am so gutted! :(

[ricstew]

First I would double check your camera settings......does the 600d have focus fine tuning? Can that have been set inadvertently ? Then I would see if it still did it on someone else's camera if possible and then if all that fails send it to the man to be fixed :( Is it underwarrenty?
phooey
cheers
Jan

[I @ M]

Does that lens have a manual / auto focus switch?

Have you accidentally knocked that switch to manual focus?

[Cage]

Have a look at this link.

http://www.sigmaphoto.com/news/auto-focusing-issue-affects-limited-number-of-sigma-telezoom-lenses

[98kellrs]

Rickstew, not that I'm aware of but I'll give that a look. I had a quick scan of the settings and couldn't see anything out of the ordinary.

I @ M, yes indeed it does have a AF - MF switch and it's definitely switched to AF.

trublubiker, Thanks for that link! I'll check the serial and see if that is a possibility.

If not then it looks like I'm going to be one of those struggling to get my gear fixed under warranty by an grey market vendor....wish me luck! :(

[peterb666]

I have the 150-500 and have several friends witht he 120-400, none of them had had focussing issues. My own lens has a build number after the service advice anyway.

If the grey market vendor is from Australia and you have physical contact details you may have some hope. I expect C.R. Kennedy won't fix it for free and you would then probably find a good repairer to be the best option. Good luck as it is an excellent lens.

BTW, do you have an issue with AF when not panning? The only panning I normally do is for surfing shots an more often than not I use manual focus and pre-set the focus so there is no delay focussing after tripping the shutter.

[98kellrs]

BTW, do you have an issue with AF when not panning? The only panning I normally do is for surfing shots an more often than not I use manual focus and pre-set the focus so there is no delay focussing after tripping the shutter.

It doesn't hunt as much when shooting a stationary object, but as you can see from the cropped image in the OP, it's far from crisp. It beeps to tell me that it thinks it's in focus too.. so perhaps the camera is having difficulty communicating with the lens?

Unfortunately the grey market vendor is from Hong Kong, however they do offer their own 2 year warranty on all lens purchases so I'm hoping they stick to their word. It's a bit of a bugger though as I've got a tonne of motorsport events lined up in the coming months!

(P.s - yep I absolutely love Sigma's long lens lineup too, it has been an absolutely brilliant up to this point.)

[William]

I've used the 120-400 for surfing shots (Thanks Andrew) I found that for panning and high shutter speeds I switched the IS "OFF" Images sharp as a tack , Worth a try

Look here : http://www.ausphotography.net.au/forum/showthread.php?80090-quot-Quiksilver-Pro-Board-Riding-Comp-2011-Snapper-Rocks-quot

[98kellrs]

Thanks William, i'll give that a shot when I get back from work and see what happens. I really am hoping that it's something simple like that! :eek: