Okay, I'm not starting a 10D focus problem strand I PROMISE! but if you have a 10D you might want to be aware of this possible issue:
I recently bought a second hand Sigma EX17-35mm from Patrick at Aperture in London which would not stop down as it required re-chipping. He changed this for another example and I went merrily on my way. Unfortunately I got mixed results, ranging from pin sharp to seriously out of focus but I couldn't nail down why. I found out that at 35mm it was fine but at 17mm it was front focusing about 10-20cm. I took the lens back and Patrick gave me a full refund. I then went to Jacobs around the corner and bought a brand new lens having done a quick test and felt things looked just about there. However, when I got home and had the chance to do some proper checks the new lens also exhibited the same problem. It was fine with my EOS 3 and My back up EOS 30 but on the 10D the lowest end of the lens was way out. After a frustrating hour of tripods, high contrast targets, lights and tape measures I found that as the lens barrel moved back from 35-28mm the focus ring barely moved when I stopped to AF. However, beyond 28mm, crucially as the lens barrel starts to move forward in order to zoom out, the focus ring started to fluctuate by big measures. At 17mm with the camera on a pod, locked off and pointing at a static target AF was out variously by 10-20cm.
I contacted the charming Daniel at Sigma who took it all on board but denied that they were aware of a problem (which I genuinely believe). I went to my local dealer (Harpers in Woking) and tried a 15-30 Sigma which exhibited the same problem. Today I returned to Jacobs receipt in hand and they agreed to change it, but at the time there was a customer about to buy a 10D and 17-35mm who overheard. I told him not to take my experience as gospel but just to test the lens/camera combo to make sure. I had a charged batt which I gave him to try it out. His 10D and his 17-35 had the same problem, as it did with my 17-35 and two 15-30's that were also in the shop. I tried all possible combinations with my camera and I still had the same problem. Because the shop did not see this as a fault with the lens I could only get a credit note and ended up paying top dollar for an L series 17-40 which works fine...as it bloody should do for �700!! I have let Daniel know about this situation but would be interested to hear if anyone else has had this problem, if only so Sigma will take notice and can modify what is otherwise a really good lens. I have noticed a revised version of the lens being available, though I don't think its in response to this issue.
I'm very aware of the consequences of defaming a large american company so can I just say that this has been my experience which I recount as accurately as possible and appreciate that this may be a freak occurrence amongst a small sample of cameras or lenses.....gulp!
Sorry about the long e-mail!
Calvers www.soma-design.co.uk 07876 645 355
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