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01-22-2009, 02:40 AM   #16
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Ah, ok, now I think I understand what's happening.

It's not center versus matrix.

When you half-press and move around, matrix metering is on and measures.
Now you turn to the light bulb and half-press again.
This activates the center AF point and then it links this AF point to the middle section of the metering matrix.
This is roughly equivalent to spot metering.
It is no wonder that the values change drastically, when the middle section is filled by a light bulb.
This behaviour is exactly what "Link AF point and AE" should do.

01-22-2009, 04:22 AM   #17
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I'm okay with this behavior too...

But what I don't understand is why the metering differs between half-press and released, without composition or scene changes?
And why does it behaves differently with the peripheral AF points???
01-22-2009, 04:44 AM   #18
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QuoteOriginally posted by dlacouture Quote
I'm okay with this behavior too...

But what I don't understand is why the metering differs between half-press and released, without composition or scene changes?
Because you have told the camera to link AF and AE. The AF is only "live" when you press and hold the shutter button, so when you do this you get the exposure biased for the centre focus point....ie the bright light bulb,,,ie 1/1600 sec

When you release the shutter button, you still get meter reading for 10 seconds(or however long you have set), but because the AF is not "live" the metering has no reference and defaults to normal matrix metering.... ie 1/60

Seems perfectly logical to me.
01-22-2009, 04:46 AM   #19
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Because only at half-press the AF is active and apparently only then "Link AF point and AE" is operative.
You can test this by setting the AF to Selective and, at half-press, wander through the AF points. Then the metering should change accordingly.

01-22-2009, 05:51 AM   #20
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Pschlute, I'd agree with this if the AF mode was on Auto, but this is moot in the Select or Center modes, as the body already knows which AF point is in use... Or maybe that's something they have not really thought about at Pentax, and even in Select or Center mode, Matrix Metering retrieves the focus point only on half-press...

But, going this way, using any other AF point should lead to a similar leap...
Say you're using bottom-left AF point, and use it to focus on the bulb, then (theorically) you will see a similar leap with "link AF point to AE" enable.

But you don't have such dramatic differences using the other AF points (and I've tried!).

I guess I'll stay away from Matrix metering, or at least the "link AF point to AE" feature...
01-22-2009, 08:20 AM   #21
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QuoteOriginally posted by dlacouture Quote
Pschlute, I'd agree with this if the AF mode was on Auto, but this is moot in the Select or Center modes, as the body already knows which AF point is in use...
True. I guess they weren't expecting anyone to be concerned about this. In four years on these forums, it's the first I've heard anyone bring it up.

QuoteQuote:
But, going this way, using any other AF point should lead to a similar leap...
Not necessarily. The "link" option doesn't turn the camera into a spot meter on the chosen focus point; it merely gives it added weight in its calculations. And it kind of makes sense that it would be hesitant to give as much added weight to objects that are off center.

QuoteQuote:
I guess I'll stay away from Matrix metering, or at least the "link AF point to AE" feature...
I don't see why - it's doing exactly what it should, and it's often a very useful thing. Mind you, I don't use matrix metering either - but that's because I like the way center-weighted metering allows me to get a reading on the scene as a whole as well as finding out something about the light and shadow areas individually - it works very well for those of us using M mode mostly. But if I were using an auto mode and wanting a single exposure reading for the scene, I'd probably be using matrix with the "link" option.
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