Can't focus... lens, camera or other?

Rocketman766

I noticed the other day while taking some shots at a parade, that the focus could not be achieved. I had my Tamron 28-75mm f/2.8 on my 1DMKIII. I started out with iso 400 but had to work up to 800 as the evening went on. I noticed a few times that I had the distance at 75mm and if I dropped it down to 70mm and tried to refocus, it did not hunt for focus like it had just prior to that. Does this sound like an issue with the lens or with the camera? I checked the contacts, they appeared clean. What else should I look for? It wasn't a low light situation, or at least I didn't think so. I was using ss ranging from 1/640 to 1/2500. Any help would be appreciated. Thanks, Lance.

pathfinder

I would try this lens on another camera body and see if you can duplicate the issue. I doubt you have this happen with your other Canon lenses on your Mark III, but if it is the body then you would expect more than just the Tamron lens to be affected. The Tamron 28-75 is a fine lens, it was one of the first lenses I bought in the Canon system. I still use it from time to time. ISO used should not really affect auto focus unless it is getting dark enough to see, and your shutter speeds certainly do not suggest that dark to me.

I would clean the electrical contacts again, and check that you do not have AF turned off on the lens inadvertently - it happens sometimes.

If the lens duplicates this behavior with another body, then I begin to think the lens is at fault and will have to go to Tamron service. I had my Tamron 200-500 cease working entirely and abruptly for no apparent reason. Tamron service returned it to life and it functions flawlessly for that past few years - I shot this gallery, among others, with it

Richard

I agree with PF's suggestions. Don't forget that Tamrons have a six year warranty, which is fairly awesome--it might still be in effect.

Rocketman766

Thanks for the help here, I would have replied earlier, but my day job got in the way... I will try the lens on my Xsi, and also will watch for it on my other Canon lenses with the MKIII. I learned my lesson (but it still happens) about the AF switch. When I feel the need, I put a small piece of tape over the switch. I don't think I explained the problem properly, but the lens was hunting for the focus from one extreme to the other constantly. I could hear the motor and see the image changing in the viewfinder. I will clean the contacts again and see what happens. I never rule out operator error, so I will just go shooting some more and see what happens.
Once again, Thanks for the help. Lance.