A general question that's been bugging me -- how do focusing screens work?
How does it 'know' to move the central split-image sideways if it's out of
focus (and how does it know to move one side one way and the other the
other?) What makes that bit go dark if the aperture's too small?
How do microprisms work? (I know what they do, but how do they do it? Are
they just like a whole lot of small split-image bits?) How is it that the
1-1 screen goes dark at f5.6, but the 1-2 screen goes dark at f8, even
though they're otherwise identical? (at least, that's what it looks like
from the eSIF page on this). Does this imply they could make a screen that
goes dark at f16?
The eSIF page also mentions that the completely clear screens don't provide
depth-of-field info -- again, what's going on there? How does a clear screen
work at all (and what is it about the texture on non-clear ones that _does_
provide DOF?)
Is there some sort of general description of this somewhere? I looked for
web pages, but the best I could find was an astrophotography screen that
explained knife-edge focussing and mentioned normal ones in passing.
thanks,
-- dan
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