While reading CR's new review of the Sigma 24-105mm lens, I saw something that gave me pause...
In the Sigma 24-105, their version of Image Stabilization (OS):
...OS is always activated on this lens, something that differs greatly from Canon lenses, which only activates IS when focusing and tracking.
That got me thinking of how Canon's way of activating IS (only when focusing & tracking) affects me while I'm using back-button-focus... In Canon lenses, does Image Stabilization stop
once I release the back-button-focus? With back-button-focus, does the shutter button
continue to have any
roll in IS? How does this IS behavior fit-into a focus/recompose workflow? Do I really have to keep the back-button depressed until after
I've recomposed & taken the shot(s) in order to keep IS active?
The fine-print in the User's Manuals of the Canon IS lenses states:
If you set the camera's Custom Function to change the assigned button to operate the AF, the Image Stabilizer will operate when you press the newly assigned AF button.
As I read this, with the buttons on my 5D3 reassigned for back-button-focus (the shutter button set for "Metering Start" and the AF-ON button set for "Metering and AF start"), IS is activated when I press the newly assigned AF-ON button; okay, I get that. But this statement does not necessarily
mean that IS immediately stops when the back-button-focus is released, or that IS is de
activated in the shutter button when reassigned to a back-button. So I'm left wondering what is the correct way to use the focus/recompose technique while still keeping the IS active during the shot. Is there a delay in the IS turning off after being activated by a back-button-focus? A lot if "internet people" claim that this is the case... Does the (half pressed) shutter button still retain its IS function when AF is reassigned to a back button? Or is the only correct way to focus/recompose with back-button-focus is to keep it depressed all the time while shooting?