I don't know whether 1st or 2nd-curtain sync would make a difference a
film camera's automatic mode ambient exposure or not. Probably depends
on the camera and the mode. But unlike our beloved OM's, no DSLR on the
market measures light reflected off the sensor during exposure. Like an
OM-1, all light measurement takes place in the pentaprism area. During
an exposure the mirror is up and the camera's meter is blind.
Therefore, any flash and ambient exposure combination in a DSLR has to
be computed before the shutter is fired. That being the case the sync
timing of the flash would make no difference to the ambient exposure.
The fact that the DSLR meter is blind during the exposure accounts for
the pre-flash needed to measure flash output or else feedback from the
lens on focusing distance to be able to compute required flash power in
automatic modes.
Chuck Norcutt
Chris Barker wrote:
> Chuck
>
> I agree, but if the flash does not fire immediately, the shutter stays
> open long enough to pick up more light, then closes when the flash
> fires. Presumably 1st curtain sync is designed to go off after a
> certain amount of time. This is as explained in the manual, very
> simplistically, of course.
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