writes:
<< I had been wondering about this, so thanks for the explanation, Tim. I was
getting the impression somehow that the 2N was actually "better" at TTL
flash than a 2S. But these are really statements more about the display
than about the exposure itself, is that correct to say?
>>
Joel,
Yes, but Paul or somebody previously posted that they felt the 2N
gave then a wider range of Fstops with correct exposure. In reality it all
depends on the propagation delay of the comparator circuits that send out the
quench signal. As the required duration gets shorter and shorter the
propagation delay of the circuits gets to be a larger percent of the total
flash exposure time and this percentage is approximately a percentage error.
It is a little more complex since the flash light output vs time is a highly
assymetric bell shape of which the time duration depends on the inductance
used in the particular flash. So for a given light energy, flashes with long
duration work more accurately with the cameras. To compensate a bit for
comparator delay as a designer, you can add some phase compensation to
effectively predict a bit ahead of time from the integrator rate of change
when to cut off the flash to compensate for delay. I don't remember whether
they do this in the cameras. The camera with the fastest comparator will
allow the camera to be used nearer the subject with smaller error. If you
have a flashmeter you can actually place it at the film plane and test
whether the 2N is better than the 2s in this regard. You would need to put a
diffuser in front of the meter to provide a reflective surface for the OTF
to work.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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