I have a Canon 7D Mark II and the Canon EF 100-400mm f/4.5-5.6 L IS II. I also have the canon EF 1.4X extender and I can get autofocus with this combo with the center point plus 4 surround points.
I have my Camera set to beep when I achieve focus.
I am thinking of getting the 2X extender. I know I can’t get Autofocus with this. What I want to know before I buy is if I manually focus would my camera still beep or show the AF confirmation in the viewfinder when the lens is focused on the target?
No, you won't. The AF doesn't work because the AF system is not in proper operating conditions, and focus confirmation and AF use the same source.
Tested this on my own setup (Sigma 120-400 f/4.5-5.6, 1.4x extender, EOS 70D): I get neither AF nor focus confirmation at the long end (f/8), but I get both at the short end (f/6.3), and they disappear at the same time.
Short: Yes, IMHO you will get focus confirmation.
Long: If you do not press anything on the camera you will not get any AF confirmation. And for me the reason is sample: the camera processor do not get anything from focusing subsystem.
But if you halfpress the shutter or press the back button (if you use back focus button) you will get confirmation (tested with EOS 5D MIII, same lens, w/o extender). And the reason is focusing subsystem is activated and processor receive signals and can get when the focusing point(s) get the focus.
I do not have information what will happen with extender (x2) because the resulting aperture will be beyond F8 but IMHO this is limitation of autofocus, not focus confirmation so you will get it.
It depends on the camera and TC, but the 7D MkII disables the PDAF module function at f/8, whether it's an effective reduction or physical reduction; when it is disabled you get nothing from it. But if you use a TC that doesn't report aperture (3rd party or tape over the pin) it will continue to function at f/8 and beyond.
Rather, I should say that it will attempt to function regardless of the effective aperture. The reason AF is disabled at smaller effective apertures with TC's is because the images the AF module receives become too degraded to be useful; reduced sharpness/contrast/brightness/etc. The AF becomes very unreliable...
