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Flat-field Correction

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Being curious I thought to see what the new "flat-field correction" does for me. As it turns out, maybe nothing. It's always (as far as I can see) greyed-out. Anyone know why?
 
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Have you read the instructions on how to create a flat field corrected DNG? You need to select two images: one normal image taken with the lens, and one image where you covered the front lens with a diffusor.
 

PhilBurton

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Have you read the instructions on how to create a flat field corrected DNG? You need to select two images: one normal image taken with the lens, and one image where you covered the front lens with a diffusor.

What can we use for the diffuser?

Phil Burton
 
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What is the difference between using this filter and shooting an 18% gray card? Can you do flat field corrections using an 18% gray card instead?
I guess you can, but you would have to make sure that you use a perfect illumination source. Even the slightest unevenness in the illumination will cause a problem.
 
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The idea is that you need to make a photo of a completely uniform surface, so that any light falloff you see is caused by the lens or the sensor, not by the light source or the surface itself. The LEE diffusion filters don’t do that, unless you would stack a few dozen on to each other. The ExpoDisc does create a uniformly lit image.
 
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