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ZOOMING vs EXPOSURE Canon 10D


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I have purchased a 10D a few days ago. Having read plenty of posts

about AF/exposure issues I took it out for a quick shoot. I

performed great but, I did notice this: frames taken with the Zoom in

the TELE end were slightly UNDER exposed compared to the same shot

take on the WIDE end. I used a 24-70L f/2.8.

 

I would expect (if anything) the opposite to happen, since the wide

shots would include more of the sky. All I can think of is that the

CMOS is reacting differently to the change in size of the subject.

 

Any thoughts/comments are welcome.<div>005pLL-14182284.jpg.e8c6eb27e811a8d82b8952058130b231.jpg</div>

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One scene happens to tip the evaluative metering algorithm to a darker exposure than the other. If you filled the frame with a gray card (or equivalent) under the same lighting I'd expect both ends of the zoom to yield the same exposure.

 

What you're really asking about is the nature of the algorithm used for evaluative metering. Unfortunately, I have only a vague idea exactly how that metering mode makes decisions. You could test a lot to get a feel for how it works, but it's probably easier just to keep an eye on your histogram, bracket key shots, or use partial metering when you need it.

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Shoot a grey card (or a white card). If you get the same expsoure on both, it's the metering algorithm that's changing exposure not the lens.

 

A 10D isn't a $1500 P&S camera, you will need to learn how to use it, when to trust evaluative metering and when to use partial or centerweighted and when to use exposure compensation.

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Bob, thank you for your comments. I am not comparing the 10D to any cheap P&S digital (or otherwise). I have gotten some great pix with from the start. I was just wondering why the change. I have also had two 'misfiring', for lack of a better term: shots that were totally underexposed. That's out of over 500 pix I took so far.

 

I usually use the partial and/or manual compensation 'on the fly', depending on the scene. In this case I am just talking about the camera behavior itself, not necessarily noting it as a BAD issue.

 

Here's a pix taken on the fly on the same day, with the same lens (24-70L) using partial metering.

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Just a thought - are you SURE it was evaluative metering? Your examples make sense assuming center spot metering (or whatever Canon calls it) is being used.

 

On the Canon Powershot S series digicams, the symbol used for evaluative and "spot" metering can be confusing. Many thought they were reversed. It took experimentation and emails to Canon support for the www.dpreview.com forum community to figure it out.

 

I have no idea if the same icons are used for the 10D, but you might take a close look at the manual. In the case of the Powershot S series, the manual was correct, though the icons used seemed counterintuitive to many.

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THe exposure is biased to the auto-focus point that is active. You may find that the af point is reading off of a different part of the scene in each case. Shoot some in raw mode then use the canon file viewer program to preview the shots with the auto focus point visible and you'll get a better idea what is going on.
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