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06-24-2009, 08:00 AM   #1
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Riverlady's Avatar

Join Date: Mar 2009
Location: Austin, TX
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K200D exposure bias

In a photo class last weekend we shot a gray card in full sun, I was using the long end (250mm) of my Tamron 18-250 and filled the frame with the card. (AV mode, no exposure comp.) Much to my surprise, the histogram indicated that the camera was overexposing by 0.3 stop. My general feeling after using this camera for about six months now is that generally it tends to underexpose, and that seems to be the consensus from what I've read online. My teacher, who has decades more experience than I, says the bias should be the same no matter what the light, or what lens is on the camera.

So, I am curious to understand this... wondering if maybe the explanation is that more often than not in real life I am metering in difficult situations that have a wide difference in the amount of light in various areas of the scene like mottled shade, mixed sun/shadow with lots of glare (e.g. arroyos) with dynamic range on, which I believe (is this correct?) underexposes in order to protect highlights. Also that even tho the camera may have a +0.3 bias with a gray card, often I am shooting scenes that require compensation for a specific lighting or subject situation that also must be factored in.
Any thoughts?

06-24-2009, 02:10 PM   #2
Marc Sabatella's Avatar

Join Date: Sep 2006
Location: Denver, CO
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You're really seeing the histogram spike right of center when metering off a gray card that fills the frame? That would be quite unusual.

Even so, how the amera meters gray card has little to do with exposure of real world scenes. I the issue with real world is preciely that it is *not* a gray card, so there is no One True Expousre for an given scene. Sure, the one chosen by the camera is often darker than the one you'd prefer, but that's not "underexposure" per se - that's just the camera not reading your mind.

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