@BobInPA wrote:I’m going to be trying my wife’s Canon T4i camera and I have a settings question. If I have the mode dial on the Creative Mode Zone “Av” setting, where should I set the lens’ focus mode switch — in the AF autofocus or MF manual focus position? If either option is fine, any observations about the benefits or drawbacks of either choice when in Av mode?Thanks.
Either option is fine. Av is an exposure selection mode, not an autofocus mode. There are different autofocus modes, and it's important to read the manual carefully enough to understand their behaviors if you want to get the most out of the camera's autofocusing capability. But they're not directly related to how the camera goes about selecting the correct exposure.
Unless you have a very good eye & can manually focus through using the viewfinder (& without the old style focusing aid older cameras had built in) or know how to use Live View set the switch on the lens to AF. When you half press the shutter button you will see that the lens focuses on your target & all you need to do is finish pressing the rest of the way to take the shot.
Bob and Cicopo already gave you sound advice...
In general you always want to use auto-focus whenever possible. There are a few exceptions, but not many (e.g. it may be better to use manual focus when shooting landscapes because there's really no single point of focus ... you want the whole scene to be focused and there are ways to optimize the focus area when using manual focus (and a high f-stop).
Also, you should keep the camera in "One Shot" focus mode for subjects that aren't moving (camera to subject distance isn't changing) and use "AI Servo" mode for subjects which are moving.
"Also, you should keep the camera in "One Shot" focus mode for subjects that aren't moving (camera to subject distance isn't changing) and use "AI Servo" mode for subjects which are moving."
I would take this advice a step further and say you should keep it in One Shot until you are more familar with how the Rebel T4i and photography, in general, works. It is better to do a few or one step at a time instead of adding severl factors all at once. KISS.