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01-15-2012, 12:26 AM   #1
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Exposure (metering) different in liveview versus viewfinder?

This might be common knowledge, but couldn't seem to find an answer. I was fiddling around with liveview on K5, and it seemed like the exposure values for using liveview seems to be different than using viewfinder - for the same scene and light conditions (aperture and ISO remaining the same)

E.g.
For F4 and ISO 100
Liveview would show an exposure of 2.5 seconds
Viewfinder shows an exposure of 2 seconds

I am using contrast AF along with my FA 77mm lens.

I would presume that for the same parameters, the exposure should be the same, but I can't seem to anwer this difference. What am I missing here?

Thank you!


PS: Same results with and without SR.


Last edited by pentaman; 01-15-2012 at 06:55 AM.
01-15-2012, 12:56 AM   #2
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I have noticed that too. I suppose the underlying difference is using the dedicated exposure sensor (optical viewfinder) vs. the image sensor (LV) readings as inputs to the exposure calculation. While it should be possible to emulate the former with the latter they (Pentax) are probably trying to use the latter to an advantage (more information is available, after all) and hence the algorithms are different, as are the results. In general, metering (and auto modes based on it) is supposed to get you close enough (most of the time ) and both methods would seem to be doing that.

Last edited by jolepp; 01-15-2012 at 03:40 AM. Reason: typo
01-15-2012, 03:08 AM   #3
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They both use different ways of calculating light levels. I know this because when I changed my focusing screen my photos are now consistently over exposed when using the view finder while they are "normally" (as in exposed the same as I was used to before changing the focusing screen) exposed using live view. So I believe that when using the view finder the camera uses a sensor behind the focusing screen while when using live view the camera calculates the lighting levels based on the actual image sensor.
01-15-2012, 06:54 AM   #4
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Theoretically, the metering (and exposure) should be the same no matter how you measure it - the light coming to the sensor at the end is the same. But it does make sense now - that people recommend a + EV compensation. That would also mean that the metering off of LV is more accurate.

01-15-2012, 07:55 PM   #5
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i have also noticed this in my K-x. The live view will expose between +0.3-0.7 more than the viewfinder.

Also if you have Live View on with Phase Detect and Continous AF, the picture will be taken with the metering from the Viewfinder, because in this combination of modes, live view turns off for a second when focusing, and stays off until you fully press the shutter, so the final exposure for the shot taken comes from the view finder.

If you use Phase Detect with Auto AF, then after focusing the live view comes back on, and the exposure for the shot comes from the live-view.

I find it nice to have the focus on AF.C, phase detect. Because this way you can use live-view to compose, then AutoFocus and take the picture with no double flop of the mirror thus reducing shake.

Last edited by mpmetro; 01-15-2012 at 08:04 PM.
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