Speaking of light bouncing around in the lens. Take a look at the back
of a lens when it is stopped down to f/16. Doesn't it seem that the
aperture blades reflect quite a bit of light? At least compared to the
flat black metal of the lens. Also, consider that the film is 18%
reflecting, wouldn't this cause similar, if not more, loss of contrast
than the single versus multi coating? I have noted that in Gary's lens
tests that sometimes the contrast is down a bit at wide open and at
f/16 and f/22. Is the lower contrast at high f stops caused by
diffraction or the reflecting aperture blades and film/first curtain?
Wayne
Very interesting. You are right that aperture blades, even though
darkened, are still shiny. That could be significant. And any
exposure faster than 1/60 second will have the pattern on the first
curtain reflecting light onto the rear lens elements. I wonder
whether the light level in the mirror box is so low compared to the
outside that maybe it is not significant after absorbtion by the
matte black surfaces. Light hitting the rear lens element which is
multi-coated and curved would have reflection thrown to the side of
the mirror box, I think. Since the field of a lens is circular, not
rectangular, even the large one on a shift lens is apparently well
absorbed by the walls of the mirror box.
--
Winsor Crosby
Long Beach, California, USA
mailto:wincros@xxxxxxxxxxxxx
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