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Old Dec 20, 2006, 9:26 AM   #1
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Finally broke down and bought this flash yesterday. Took a couple of test pictures this morning with camera set on P and flash automatic. Exposure seems good on the few shot I took, but I have a question. With the camera at any focal length say 70mm the flash display reads about about 20mm more ... this seems consistent through the range with a couple of different lens (Pentax 18-55 and Sigma24-135) that I've tried. Is thisnormal, or should both focal lengths be more or less the same?

Cheers, Mike
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Old Dec 20, 2006, 11:07 AM   #2
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Hi Mike,

I don't have the flash, so I'm just guessing. AF flashes try to compensate for different lens focal length lenses by modifying the angle of coverage for the flash (wider for shorter FLs, and narrower for teles) to prevent dark edges and provide maximum light for the subject . I'm thinking that Sigma, in programing their flash, is trying to compensate somewhat for the narrowed Field of View with the 1.5 crop factor in 24x16 sensored cameras. Since it will deliver a greater angle of coverage than whatever lens you're using, the only negative is that you might be wasting a little of the flash's output. Pentax flashes don't do this, and return the correct FL of the lens, so in this respect, the Sigmas might be a little more efficient (but not to any really significant extent).

It's something that I wouldn't worry about unless you're finding that causes more exposure problems than are normal for these automated flashes.

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