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09-25-2011, 09:31 PM   #1
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K-7 CW metering vs Matrix metering

A quick question as I am finding my K-7 is acting up strangely lately.

If I meter the blue sky (no clouds, evenly blue) using CW metering, I will get a reading which is lower than if I use matrix metering.

So I meter the blue sky using CW metering and shoot, my scene is about 1 stop to 1.5 stops underexposed as compared to metering the sky using matrix metering...is this correct?

I would have thought CW metering and matrix metering will both give the same reading on the same blue sky....

Thanks for any pointers..

09-25-2011, 10:00 PM   #2
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Well, for an average scene (zone V) you found your camera should have about +1.5 ev (actually likely more).
And one problem with matrix metering is one is never sure how it comes up with it's reading--but in this case the matrix of readings (separate areas) are all the same--so presumably it knows the scene is likely one light value--so it is placing it higher than zone V (somewhat like ETTR) .
09-25-2011, 10:10 PM   #3
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sorry..i am a little confused...should I be expecting the CW metering and Matrix metering (both meters the sky the same blue colour all over) to give different readings?
09-25-2011, 10:18 PM   #4
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The classic problem is metering a back wall or a white wall. Center weighted simply gets one reading and thus has insufficient information to do anything but try and expose it as thought the scene was an average middle grey wall.
Matrix metering obtains a number of readings (breaks the scene up into separate areas) and then uses some logic to decide what kind of scene it is. Presumably if the upper areas are seeing much more light than the lower ones--it says "Oh it is a bright sky so I should place the sky on zone VIII--and thus I should increase the exposure." Apparently the logic employs a large number of scenes and what the matrix reading vs required reading would be.

09-25-2011, 10:24 PM   #5
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And to repeat my first note--if all the areas have the same light reading (middle blue sky) the (matrix reading) logic says "Oh the scene is all the same--so I should push the exposure to get more detail." It's a question of having several pieces of information so additional inferences can be made.
09-25-2011, 10:46 PM   #6
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So what kind of metering should i use to meter the sky? Matrix metering then?
09-25-2011, 11:10 PM   #7
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What kind of metering should you use has to do with your knowledge level. I don't use matrix metering because I want to know exactly how the camera came up with the exposure--that way I am in control and also I learn for the future. But I am old school and very into exposure theory.

I suppose the best approach for you is to start with matrix metering--but realize (for the future) there are situations where weighted average, spot metering, and biasing the reading by +/- 1 or 2 ev, or not using the meter at all (so called sunny 16 rule, etc.) are best. And for this you need to do some homework.

Although you are not doing B&W film I still think Ansel Adams, (Book 1) "The Camera" gives the best description of variation of light in a scene and what it means. I also like "Exposure Manual" 3rd edition by Dunn. These are very dated references--but the theory has not changed--and I don't know of any good recent reference.
09-25-2011, 11:28 PM   #8
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I have always gone with what i learn from the book "understanding exposure" where i am metering from the sky.....it has always work for me in centre weighted metering mode but for whatever reason, my last 2 shooting outside with this exact method ended up with underexposed scene. I am just keen to know what went wrong or what I did wrong.

09-25-2011, 11:48 PM   #9
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All I can tell you is: if I was shooting an outdoor scene with a clear blue sky with my K20D I would use spot meter of the blue sky (not near the sun) and add 2 e.v. to it. Basically your weighted average + 2 e.v. (which is about what you said!).

But (1) I use camera raw and am forcing the white highlights (if any) to overexpose and fix it in camera raw, and (2) my K20d already exposes by about + 2/3 stop (e.v.) b/c I have a istD screen in it.

There is no simple answer--pick a metering method and then shoot at +1 ev. +2 e.v. -1 ev. etc. and decide which is best. The camera is a dumb imperfect device.

Or simply accept what ever it says (use it as a black box) with matrix metering--as I said before.
09-25-2011, 11:55 PM   #10
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If the camera is not consistent with past history--maybe you now inadvertently dialed in a -1.5 e.v. (about) adjustment? Since the readings you get now seem reasonable to me it does not sound like the camera is in serious error. Hope this helps.
09-26-2011, 12:09 AM   #11
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Nope. I did not accidentally dial in a -1.5EV adjustment. I doubled check many times to make sure I did not do something silly like this.

I will test again with my K-7 and return with my observations. Thanks dms. appreciated.
09-26-2011, 02:03 AM - 1 Like   #12
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I hate clear skies. I hate metering and shooting clear skies. I try my best to avoid clear skies. At worst, I ignore clear skies. I meter the subject instead. If I can't meter the subject and it's about the same brightness as something around me, I meter that instead: my hand or sleeve or the ground or whatever. If I'm shooting varied 'scapes under consistent light, I manually meter a subject, then leave the exposure there. I'll trot-out this example again:

Last year I shot in the Red Rock country around Sedona Arizona on a bright spring-summer day with blue skies and white puffy clouds. I metered the rocks, vegetation, structures etc and got a good exposure. Then I locked-down that exposure and just shot. If I'd left metering on Auto, whether Spot or CW or Matrix, exposures would have been all over the place, depending on just how much rock-vegetation-sky-cloud-etc was in any frame. Instead, I got consistent exposures in consistent light.

I take that same approach with any clear-skies 'scapes. It works.
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