That's the best name I could come up with for this, but I tinkered around with the custom controls, and I "discovered" feature if you set it up right.
Imagine that you're framing a scene with two animals squaring off. Each located on a different corners in the viewfinder, and at different distances to the camera. You want to focus and snap each of them in quick, staggered shots, depending on which one is doing something interesting. Traditionally, you would need to turn either the finger-wheel or the thumb-wheel to change AF points, and then focus and take the shot. But with this feature I discovered on the 7D, you can have two AF points, each covering one of the animals, and have two dedicated focus buttons, one for each animal.
This way, when you need to quickly shift focus between the two animals, it's a simple button click instead of turning the dial and then focus.
So the way to set it up is this:
- Go to the Custom Controls menu.
- Set the 1st button <Half shutter> to [Metering Start] only. This will remove the 1/2 press focus function from the Shutter. It will only act as shutter release.
- Set the 2nd button <AF-ON> to [Metering & AF Start]
- Goto the 3d button <*>, and also set it [Metering & AF Start], but at this inner options screen, press the <INFO> button, and it displays one more screen.
- Change to the 2nd option: [Registered AF point]
- Set all that and exit.
Assuming you know how to memorize AF points (see pg 219 on "Registering and using AF point"), all you need to do is to memorize an AF point that covers one subject, and the <*> button will now always focus using that point, no matter where your current AF point is.
You are free to move the current AF point around and use the <AF-ON> button to focus that exclusively. And if you need to quickly switch focus to the other point, just press <*>. So basically, you can toggle focus between two spots instantly! (of course you'll still need to press the actual shutter to take a shot).
I dunno, but this seems revolutionary to me. It would have made for a rather impressive commercial, but they didn't even mention this possibility anywhere. It uses several features that are new to the 7D, but the combined effect is amazing.
I was already impressed with the 7D's "Orientation linked AF point" feature. Combined with the Register AF point feature, and my "Simultaneous dual AF-point focusing" feature, the possibilities are staggering!