I have a Sigma 50-500mm lens and when I go to auto focus it keeps stopping and starting. The lens is making a clicking noise when it is auto focusing.. It works fine in manual focus.. Can anyone help please??

hi

So you are getting clicking sound from the camera lens ok....

First of all does the lens come out completely from the camera?

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.

dos the manual focus work

Hi is the manual focus working from inf to close focus and not stoping then it needs a new hsm motor

needs a new hms motor

If you just purchased the lens I would take it back sounds like the lens is jarred and defective should still be on warranty

Hi    The switch is held on by two screws you can remove the screws    and the switch will fall off it will need cleaning 

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.

let me know how it works,
Caleb

A dirty filter, front, or rear optic can cause the lens to seek