EF-S 17-85mm will not auto focus on fuul zoom my other lenses work ok so must be this lens ? it keeps on trying but most time ends up out of focus

If the focus works OK in manual focus and you are getting problems with auto focus you may have a broken or worn ribbon in the lens.

The sound may be the result of the auto focus motor operating to keep the subject in focus. You may be able to shut off the auto focus by switch on the lens (if provided) or camera body menu and focus manually instead.

You haven't stated which body you have but the AF will not work with the extender if the effective lens aperture is too low (remember that a 2x extender doubles the focal length but halves the effective aperture).

Canon's own website states: "Autofocusing does not operate if the effective maximum aperture is greater than f/5.6 (greater than f/8 on the EOS 1V and EOS 3)."

It sounds like the circuit board flex has gone bad, It folds back and forth when you zoom the lens, And needs to be replaced by a repair shop and readjusted. Tony

No quick or cheap fix, but definately a lens worth fixing- send it to Canon

If your AF motor is hunting then the lens probably needs to be looked at. I wouldn't recommend this as something to do at home so you will need to either find a repair shop if it is out of warranty or return it to Canon if it is in warranty.

1st u reset the factory setting and then u see the lense is correctly fitted or not and the autofocus option is working or the manual focusing is there or not

I see this same problem occuring all over the internet on Canon lenses. Autofocus not working any longer. For some stupid reason the lense will lock up and quit autofocus while other lenses will work fine. A light pull on the lense focus ring away from the camera body will give a noticable pop or click which unlocks the jammed lense. Try it if you are having troubles with your autofocus. This is a very common problem and worth giving it a try.

Yes, this is normal. Some zoom-lenses adjust the focus when zooming, to always keep the subject in focus. Those tends to be the more expensive lenses.
So you don't have to worry, nothing is wrong with your lens.
/Chris

I have the same problem. So far I've contacted Sigma (I believe this is the company that manufacturers the Quantaray lens for Ritz) and they requested I send them a photo of the lens. I just googled sigma lens to find sigma support. I will update you all with any response I may get.