Back button focus

[RJ]

when I use back button focus on my Rebel XSi does the image stabilization activate?

[ebiggs1]

I have not tried that personally on a XSi but I would say it does. The IS is in the lens not the camera.

[TCampbell]

Yep - if you have an "IS" lens and the switch on the lens has enabled the IS, then anytime the lens is active for focusing, the IS is also active... regardless of how you activate focusing (shutter button or back-button.)

[RobertTheFat]

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@RJ wrote:
when I use back button focus on my Rebel XSi does the image stabilization activate?

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I don't think IS is even related to autofocus; it should operate (assuming it's turned on) even if you're focusing manually. The 5D Mark III manual (which I consulted because it was handiest) says it will.

[RJ]

Thanks to those who replied and clarified this for me, It was most helpfull. I will continue to use back button focus.

RJ

[ebiggs1]

"I don't think IS is even related to autofocus;"

It is, however, related to the "button".

[TCampbell]

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@RobertTheFat wrote:

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@RJ wrote:
when I use back button focus on my Rebel XSi does the image stabilization activate?

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I don't think IS is even related to autofocus; it should operate (assuming it's turned on) even if you're focusing manually. The 5D Mark III manual (which I consulted because it was handiest) says it will.

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It is... but in a round-a-bout way.

We normally think of "IS" as a way of allowing us to shoot at slightly slower shutter speeds than would normally be safe for hand-held photography.  

Canon suggests that if you're shooting action at long focal lengths then camera movement while focusing can make it more difficult for the camera.   So... even if your shuter speed fast enough that you don't need IS for the shot, the IS system itself will stabilize the image a bit better while the camera is trying to focus.  The result is faster and more accurate focus speed.