Just bought brand new eos 4000d and attached sigma ex lens, whilst the camera works when lens set to M, it does work when set to AF .. please help
I sometimes have this problem with canon lenses. You may be very close to being in focus, whilst in manual move the focus ring so it is out of focus then put it in auto-focus and try again, have you set the camera up for rear button focus, you might be using a incorrect button. Have a look at the menu in custom button and see if you shutter button has been disconnected, lastly is the lens a secondhand lens, clean the contacts on the lens, use cotton buds or lens tissue or cloth with some Metholated spirits or something similar. The Metho is alcohol based and will evaporate and not leave a residue on the contacts.
When you say the camera does not work when set to AF, is the lens trying to focus and not finding focus? The camera will not let you take a shot in AF unless it finds something to focus on with one of the focus points. In manual focus it doesn't care if the photo is blurry. Is the sigma lens brand new too? Which sigma lens is it? As Craig mentioned it could be oily contacts so a light cleaning may help. Some old sigmas had issues with the newer DSLRs compatibility wise. I also heard of people complaining about the AF motor on sigmas not always working, and they had to turn it slightly to get resistance from the motor to get the AF motor to work again. If the Sigma lens is brand new and you have motor issues you should return it to the shop right away under warranty. Either way I think we need a bit more info to dig into the exact issue..
Thank you for your responses so far, its much appreciated ... actually, I think I may have figured it out now .. thank you Craig & Johnsey