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06-21-2012, 07:39 PM   #1
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Metering with the green button vs. the optical preview on the K5

I have a question here.

06-21-2012, 11:01 PM   #2
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Your results are correct - "Green" Button = P Line.
DoF Preview = DoF Preview.
06-21-2012, 11:26 PM   #3

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Yeah, green button will stop down in order to meter and then set the shutter speed for correct exposure. Aperture is obviously determined by the aperture ring, and ISO is also set manually. (You must set the correct menu option so green button in M = shutter speed.) Optical preview is just a DOF preview -- it does not meter, or it doesn't do anything in reaction to metering anyway (if the meter is on it is metering all the time) -- it is designed to stop down to your chosen aperture to show you what is in focus and what is not. DOF preview works in all modes and with all lenses.
06-22-2012, 06:30 AM   #4
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the real difference is that the DOF preview is just that, DOF preview. with one slight exception, the meter is activated and if you look at the +/- metering scale, you will see how many stops over / under you are, but the camera leaves the setting alone. This is useful, because it gives you a sanity check, without changing your settings. I use DOF preview, specifically when using manual lenses with flash on my *istD, (which supports TTL metering) so I can check what contribution the ambient lighting will offer in blended flash modes. The same is true when using "AUTO" flash with an AF540FGZ on newer cameras, and legacy lenses because you can again see the ambient reading.

the green button, on the other hand, will set the exposure to what the metering thinks it should be, (as you say, not perhaps what you want, but generally a balanced exposure). It will attempt to set the P line for all lenses that report focal length back to the camera, i.e. all AF lenses.

on MF lenses, it will set the shutter to what ever is needed to set the exposure

I sometimes wish, that when a flash is connected, the green button would only activate the meter as long as you held it, but that is just me.

06-22-2012, 07:18 AM   #5
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Using Pentax-M lenses I meter in DOF mode, normally tweeking the speed while holding the DOF preview. When stopping down several stops I find the "green button" often gives a less accurate setting than this method. I know they should be the same, but (at least with the -M lenses) the green button seems less reliable.

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