I see C.H. and Paul have answered some of this, but not all.
Dean C. Hansen wrote:
<snip>
When I close down to f8, the opening in the diaphragm is clearly a
hexagon about 3mm across. With the bellows cranked out, the front of
the lens is about 27cm, or 270mm, from the film plane, so isn't my
effective f-stop 270/3=90? Or is it? Is this a concern?
I don't remember enough optics to know if this is the correct formula,
but it is true that greater extention requires more exposure.
But does diffraction become a greater and greater problem at longer extensions?
No, it's a function of the absolute size of the opening and the angle
from which the light comes, not where it came from or where it's going.
To the extent that greater extention narrows the angle of view, it
should theoretically decrease the diffraction. Although the effect in
probably too small to notice in practical photography.
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|