How about Live View? In LV the exposure is determined from the placement of magnification rectangle, which you can move over nearly the entire frame. Its like a rather large spot meter with custom placement and the camera will take an exposure reading just before initiating a shot.
In LV "Live", AF will also be made at the location of the magnification rectangle, as it is contrast detect. But in LV "Quick" the AF points will be used as this is the normal Phase detect AF mechanism. Thus in LV Quick, AF location and exposure metering can be a very different places in the frame.
Mike K
There are a couple of problems with this, one, in low contrast situations, LV focus underperforms, to say the least and two, in situations involving red light (not that I can think of a red lighted situation that might call for spot metering (no hooker jokes, please!)) LV focus has it's own set of problems.
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Perhaps you are discussing Live View "Liver" AF which is contrast detect. However, I am suggesting Live View "Quick" which uses the normal phase detect AF sensor and AF points. You can select a single point or let the camera select, then when pressing AF the mirror will momentarily flip down and the camera will AF with performance equivalent to normal Phase Detect AF. The only major difference in performance is that the exposure reading will come from the sensor, in the magnify rectangle region. Thus you can move the exposure area about the frame.
LV "Live" AF is contrast based and has its own disadvantages, some of which you note. It certainly is slower too. However it has some advantages: you can move focus about in the frame, focusing on subjects at the frames edge if desired. LV Live also will work at f8 lens combinations with no pin taping.
Mike K
