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The Critical Focus Zone (in a perfect system) can be calculated by
CFZ (microns) = Focal ratio x Focal ratio x 2.2
1 micron = 0.001mm
In the real world it is often the case that the CFZ is up to a third larger than the theoretical figure. - Does anyone know why ?
Stating the obvious - the focal ratio of the system must include all optics in the imaging train.
Cheers Rally
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