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Re: Sigma 28-300 3.5-6.3 won't focus
Did it ever work on this camera?
I have seen some Sigma lenses that are auto focus on canon film cameras but then when put on the digital they dont work right. If you have used it on this camera then make sure the lens is clean.sometimes dirt on the front wil make it try focusing on the dirt. Next try focusing in manual focus to make sure the focus is working. Then take the lens off and then put it back on and make sure it clicks into place.
Let me know if none of those things work. also make sure to try focus on something close and somthing far away.
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You have not supplied enough information, however with the Sigma lenses here are a few things that could be a problem.
Is the switch from auto to manual focus set to auto focus.
Is the lens the proper mount for the camera it is installed on (meaning have you used an adapter to go from a Nikon to a Canon mount?) if so then there will be no electronic communication and the lens will only function in manual focus mode.
Is the lens compatible with the camera model? (meaning some newer cameras set the lens aperture in the camera while some older lenses set the aperture on the lens.)
Part 1 of 2 Have you installed an older "film" lens on a newer version digital camera?
Part 2 of 2 Have you installed a digital full frame lens on a Canon "S" mount with the APS size sensor with the 1.6 focal factor?
Have you changed the camera model to a newer Canon EOS
Have you updated the camera firmware recently?
Have you lightly polished (cleaned) the contacts between the camera and lens? Have you received an error code 99? Cleaning the gold contacts on the lens and camera body can be done with a clean pencil eraser and lightly polish the matting surfaces making sure no dust gets into the back of the lens or the camera body. Hold the camera lens mount down while lightly polishing the contacts same with the lens. Do not wipe clean with a facial tissue or use any type of liquid cleaner.
Also third party lenses like Sigma often do not have the compatible electronic "chip" to properly communicate with all Canon EOS cameras. Meaning if you had the lens on a Canon EOS 20D and then put it on a Canon 50D chances are it won't work.
Is the lens properly locked onto the camera body dismount and remount the lens generally solves this problem.
If non of the above isn't the problem then a trip to a repair center is needed.
How new is the lens? In or out of warranty? If out or warranty most likely solution is to find a Sigma authorized repair shop because your description sounds like the auto-focus motor gear has failed. If in warranty, check out Sigmaphoto.com for repair sites and also download the SIGMA_SERVICE_REQUEST.PDF. I've only had to deal with Sigma once on warranty matter and they were very helpful, provided UPS authorization for shipping on their nickel.
The autofocus motors in Sigma lenses that are not HSM tend to be noisy, but I presume yours is now more noisy than usual. With that, and not focusing properly, considered together, It seems to me the motor has failed or the lens parts have partially seized causing the motor to "struggle" to focus parts that are not moving as they should. I.e., once focused the motor will stop, but if the electronics are telling the motor the lens is not if focus, it will continue to try to achieve focus. Most likely, time for repair, and if in warranty, contact Sigma repair via Sigmaphoto.com.
It will default to manual through the viewing screen. It will only work on automatic, using the viewfinder. Make sure you also set the focal length (lens to shutter distance). You might also have a mf / af switch on the lens. This also only works through the viewfinder.
Your Sigma 28-300mm doesn't have a HSM-motor as far as i know. When you switch it from MF to AF, you also have to disengage the manual focusing ring by pulling it towards the camera, or pushing it away from the camera. Using the AF without unlocking the manual focusing ring may damage the AF motor.
I hope this helps,
It's probably broke then. Clean the contacts to the camera and try again. If it still don't work you can probably be sure it is likely to be a bit faulty. Check the camera has auto focus mode enabled if appropriate.
(From Sigma lens literature) Capable of macro photography, this
lens has a 1:2 maximum close-up magnification at the 300 mm focal
length. It's the ideal high performance lens for portraits, sports
photography, nature photography, and other types of photography that
frequently use the telephoto range. It also has a switch for changeover
to macro photography at focal lengths between 200mm and 300mm with a
maximum close-up magnification from 1:2.9 to 1:2. The minimum focusing
distance is 1.5m / 59 in. at all zoom settings.