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Old 01-03-2018, 11:26 PM
ErwinL (Erwin)
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ErwinL is offline
 
Join Date: Jul 2017
Location: Germany
Posts: 16
(P x FR x d ) / 1000 can be rewritten as

(P x d ) / 1000 x FR = D x FR

where D is the image diameter of the dust bunny in mm.
This is an approximation of the geometrical intersection of lines between aperture, dust grain and focus plane.

Here, the dust size is assumed to be zero, a good approximation as long as it is much smaller than it's image. Bigger dust grains will primarily darken the bunny.

Erwin
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