Throughly confused about 7D and focusing.

Started Sep 5, 2012 | Discussions thread
snapperZ
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Re: Throughly confused about 7D and focusing.
In reply to apersson850, Sep 5, 2012

The chosen focus point tells the camera where you want to lock focus. The half-press locks the lens focus at the distance from the camera to that point (eyes) at the instant you press. When you recompose, anything at this distance from the lens will remain in focus.

The eyes will only remain in focus if the camera to subject (eyes) distance doesn't change. Hence the potential for misfocus, particularly when using fast lenses, long focal lengths and close subject distances which all reduce dof.

Where the AF point goes or whether there is an AF point on the desired point of focus is irrelevant once focus is locked as the AF point has done its job and is no longer used (cf servo AF where you cant focus-recompose as the lens continually re-focuses). The camera to subject distance must remain the same to achieve the desired result.

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