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04-29-2011, 07:32 PM   #1
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Matrix vs center weighted exposure puzzle

I was messing around with my K-x today shifting between matrix and center weighted exposure settings for identical shots and noticed something puzzling. While center weighted will often give a reading of 1/2 stop of exposure change vs matrix depending on what you are shooting, on many of the photos that wind up having identical aperture and shutter speeds, the center weighted appear slightly differently exposed than the matrix shots. These are photos on tripod taken seconds apart indoors in daylight with clear sky outside. I can tell this just from looking on the LCD display. I didn't download them to look on the computer. Has anyone else noticed this? I'm talking about maybe 1/2 stop worth of exposure variation between shots showing same aperture, SS, and ISO. Seemed more likely to occur at wider apertures.
Also, I noticed that when center weighted does change the exposure vs matrix, it usually gives less exposure, i.e., higher shutter speed or narrower aperture. Overall I thought matrix did a better job for scenes of higher contrast; center weighted gave a bit richer presentation for less contrasty scenes. Anyone else have an opinion on how/when to use either?

04-29-2011, 07:55 PM   #2
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It would really help if you displayed your test scene.
04-29-2011, 08:20 PM   #3
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I found the difference between the modes to be slight but matrix seemed more consistent, so I settled on that.
04-29-2011, 09:35 PM   #4
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I believe with center-weight metering, the camera does not take the focus point into account whereas with matrix metering, it does depending on the focus point the camera is aiming at. In order to change that behavior, you can go to the custom menu to change the matrix metering set despite the focus point select.

04-30-2011, 06:51 PM   #5
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Matrix is considering the whole scene and balances the exposure based on the light and dark it sees (as a whole).
Center weighted is more on what that center is focused on..more so with spot metering.
It's more of like shooting the skin of the zebra zoomed-in wherein you only see the black and white stripes, the matrix would meter based on the whole, center weighted would meter depending if you have more black or more white stripes on that particular "center" and with "spot" metering, it would meter depending on say like, if you are focused on the just the white or just the dark stripe.
It is more like exposing on a "grey" card (neutral) for white balance rather than on a black card.
I hope what I'm saying makes sense..
04-30-2011, 08:41 PM   #6
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I don't have the K-x manual, but this, taken directly from the K-5 user manual, along with the explanations by the above members, may help. I'd suggest taking a flick through the K-x manual and see if there's a section on metering.



The way I like to explain metering, is by saying metering is how the camera "sees" a scene to determine the correct exposure, and the different metering modes are how you control how it sees the scene. E.g. spot metering, you're telling the camera to only look at the spot in the middle to determine correct exposure, and disregard everything else.
05-01-2011, 08:47 AM   #7
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Yes, I get the same result as you with my K-X. Matrix metering does a better job overall than centerweighted whereas with my GX10, centerweighted often does a better job than matrix.

Clearly the metering system has been improved on the K-X.

Specifically, the K-X matrix system gets a great balance between general background e.g. sky, and the center subject of interest in that the central portion of the image is well exposed as well as the background.

I tend not to use the center weighted system on the K-X, sticking to matrix mostly or in really high contrast scenes, using spot to get the subject, if it is a small part of the whole scene, properly exposed.

It is as if the camera is applying a tone curve adjustment to the matrix metered scene.
05-02-2011, 09:04 AM   #8
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QuoteOriginally posted by lectrolink Quote
center weighted will often give a reading of 1/2 stop of exposure change vs matrix depending on what you are shooting, on many of the photos that wind up having identical aperture and shutter speeds, the center weighted appear slightly differently exposed than the matrix shots.
Also, I noticed that when center weighted does change the exposure vs matrix, it usually gives less exposure, i.e., higher shutter speed or narrower aperture. Overall I thought matrix did a better job for scenes of higher contrast; center weighted gave a bit richer presentation for less contrasty scenes. Anyone else have an opinion on how/when to use either?
I posted this in the Firmware 1.02 thread but thought it may be relevant here -

This may well be so with your practical experience for your type of photography.

However a more objective way to ascertain whether center weighted does, or does not, give lower exposures is to use an evenly lit plain wall (no features) that fills the viewfinder frame - and take exposures with center weighted and matrix -
do they come out different?

If not, then it's the types of subjects you are photographing
(eg: the center part of the picture may be brighter/lighter than the rest -
a very obvious example: center spot lit dark stage scene).

So this discovery may be specific to you and your photography -
and may not be generally applicable for anyone else.

If however the exposures for the evenly lit plain wall are different -
then indeed it is a fault -
which should be reported to Pentax.

05-02-2011, 09:16 AM   #9
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Matrix metering regularly blows highlights with my K-x. CW is less likely to push the exposure. Changing metering modes on the K-x is cumbersome, so I almost always use CW, sometimes with AE-L.
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