On 3/24/2010 2:18 PM, John Sessoms wrote:
From: Toine
David thanks for your offer but the question isn't fringing. I would
like to know if an A lens on the A setting and on the manual aperture
setting closes it's aperture blades to the same position. In theory it
should be the same. My lens shows different closing and I'm wondering
if it's normal or some sort of misalignment.
Someone can correct me if I'm wrong ...
It may not be the lens. Using just as an example f/8 ...
I think that with the lens set to the 'A' mode the camera may not stop
the lens down to an exact mechanical aperture if the auto exposure
needs it to be a little more or less.
The camera can choose fractional F-stops that don't show on the
display ... like it would display f/8 when the camera actually sets
the lens aperture to f/8 + 1/3 stop, or f/8 - 1/3 stop.
Also, is the actual diameter of the aperture at f/8 the same for the
APS-C sensor as it is on a film frame? [note question mark]
The mechanical stop is going to be f/8 on the film frame.
Apertures are reported to 1/2 to 1/3 stops in the exif of the image and
the camera measures the exposure value before making the exposure so it
will try to match that value. The actual diameter for any aperture
value will be uniform for any lens reqardless of the film format it's
used on. The effect that might have on DOF will be different but the
hole will always be the same size.
--
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\viewkind4\uc1\pard\f0\fs20 I've just upgraded to Thunderbird 3.0 and the
interface subtly weird.\par
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