On 4/19/2015 12:23 PM, Mike Gordon via olympus wrote:
CN writes:
<<I don't see how flash sync shutter speed has any bearing on the amount of time the
EFC takes to clear the sensor. Clearing the sensor takes place before the EFC shutter is
considered open. Then it's open <<(instantly), the flash and ambient exposure occurs
and the second curtain closes.
<<What's odd about the EFC is that the sensor clearing time should place a limit on
the shot-to-shot delay time in the same way that a 1/8 second shutter shock delay means you
can't possibly go faster than 8 <<frames/sec minus the shutter speed time for each
exposure.
<<The other oddity (and I really don't know how this is handled) is the disparity in
exposure times from top to bottom with electronic first curtain but mechanical second
curtain. If the EFC is instantly open then the <<exposure starts evenly across the
entire surface of the sensor.
That's not how it actually works. When using a mechanical second curtain, pressing the shutter release starts a process
of clearing the existing data on the sensor a row at a time, at a speed to match the speed of the second curtain, in
effect mimicking a mechanical first curtain. Once the second curtain has closed, the whole image is read.
Yet, when the mechanical second curtain closes, the exposure drops unevenly across the
surface as the curtain starts covering the sensor from <<top to bottom or bottom to
top (whichever way the curtain moves). This is probably immaterial for long exposure times
(relative to curtain travel time) but not immaterial for fast shutter speeds. Perhaps
that's <<why EFC is not used at higher speeds.
The GM1 uses EFC up to 1/500, then fully electronic to 1/16,000 (yup, three
zeros)
Or maybe EFC is not instantaneous but rather it enables rows of pixels across the
sensor in a timed, rolling wave at the same speed as the mechanical first curtain. I
<<don't know.
Yup, that's how it works
Roll Out Moose
--
What if the Hokey Pokey *IS* what it's all about?
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