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05-02-2011, 09:01 PM   #1
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Exposure anomaly

I am a long-time SLR user (40years)

I have had a KD100 now I have a K-x

The K-x shows considerable exposure discrepancy when using centre-weight v matrix v live view. Far more than I experience with the KD100!

Here are 3 images that illustrate the point (in order of appearance)

Centre-weight in optical view
Centre-weight in live view
Matrix in optical view

The discrepancy is most obvious between centre-weight in optical and live view - they should be the same! In fact CW in live view is same as MTX in optical view. This behaviour is found in countless of my images so it is not just this scene.

It appears that the metering system used in optical view is differently calibrated than in live view or there is something wrong.

Attached Images
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PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
05-02-2011, 10:05 PM   #2
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Question...

Are all of the above metered with your eye to the viewfinder? There can be a significant affect on metering from light entering through the viewfinder.


Steve
05-02-2011, 10:41 PM   #3
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Original Poster
QuoteOriginally posted by stevebrot Quote
Question...

Are all of the above metered with your eye to the viewfinder? There can be a significant affect on metering from light entering through the viewfinder.


Steve
Yes, except for the live view image #2 which necessarily locks the mirror up for metering, so no optical viewing with that one.

It occurs to me that like film SLRs the the view through the lens necessarily must have with light meter near the focusing screen while the live view must meter off the imaging sensor itself.

Here are two more of a beach scene
CW then MTX

Martin
Attached Images
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PENTAX K-x  Photo 
View Picture EXIF
PENTAX K-x  Photo 
05-02-2011, 11:45 PM   #4
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With center weighted in your two new examples, you are hitting the clouds in the center of the frame. Thus giving preference or 'more weight' to the center for exposure. Matrix looks at everything and tries to make a best guess as to the proper exposure.



05-03-2011, 12:35 PM   #5
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Live View vs Optical exposure anomaly

I too am trying to get to the bottom of how the K-x meters with differing settings. Here is one thing I noticed (using matrix setting): camera is showing proper (centered) metering in Manual mode; if I then switch to Live view and look at the metering readout on LCD screen, it is no longer centered, but appears to have shifted (if memory serves, to the left). I ignore the live view meter readout and take the photo as set in manual and exposure is correct. I am using tripod for both exposures and not covering eyepiece. Have not tried this in center weighted mode.
05-03-2011, 12:44 PM   #6
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I agree with Jeff that the variation in the beach scene is to be expected, but the park scene points up another puzzlement I have found: namely, that in a scene of high(er) contrast, the center weighted exposure will appear slightly (about 1/2 stop) darker than matrix with the EXACT same exposure readings, which these two pics have. On my screen, the matrix shot of the park appears a bit brighter then the center weighted LV shot.
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