If the f-stop of a lens is (numerically) larger, the resulting image on a
focussing screen will be darker--got that part allright.
However, what's unanswered is this:
when I view thru a telescope (2000mm f:10), using various eyepieces, the
image is very bright, but becomes dark on the matt standard-issue screen
in my OM1n. Not only that, but it's only on the matt surface that the
image is dark--on the split-image/microprism aid, it's as bright as thru
the tele's eyepieces. Ditto for various lenses--no matter how slow or fast
they are, the focussing aid's image is bright as ever, and even perfectly
sharp and focussed, stopped down lens or no. It's probably a virtual
image?
How does that work? How do the focussing aids work?
Next question, also related: virtually all of the AF SLRs have a clear or
almost clear screen standard, which makes for harder manual focussing--but
they don't seem to get dark when used with variable aperture zooms.
Granted, I have less than 5 minutes total of handling two Canon bodies
with 28-80mm zooms (one was a 3.5-5.6 USM, other was a Tamron, aperture
unknown), but finder brightness seemed unchanging--albiet harder to tell
what was in focus by eyeballing the screen.
Ditto for a 60mm f:2.8 Micro-Nikkor on an N8008--very hard to focus
manually in critical work; clear finder with gridlines for copy work.
So there seem to be an inverse relationship between finder brightness and
fosussing ease. If that logic hold true, then the 2-series Oly screens
will make for harder focussing under certain conditions, yes?
Thanks,
/Acer V
--
Whole Sort Of General Mish Mash <http://student.ucr.edu/~siddim01>
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