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Old 11-03-2007, 10:32 PM   #31
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Originally Posted by JimThias
Ok, I understand the process...double exposure and you place the moon in the corner (or where ever you want it) when you zoom in. Since I've never done double exposures with a film camera, I guess I'm left with one question: How come the dark sky doesn't "mask" over the rest of the previously exposed picture? Or, does it, but the exposure is quick enough that the dark sky doesn't cover up the original scene?
Jim, it's cumulative exposure to light that matters. Dark sky can't mask because dark sky does not increase the exposure. If you tried a double exposure and the second image were blue sky instead of night and a moon, you would end up with overexposed blue sky in the final image and a loss of everything in the first exposure.

Put another way, a dark exposure does not paint the negative black! It's the absence of light, not the presence of a black shade of light.
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