Yes, I agree. I'm was forgetting that the first curtain is still
available for exposure measurement even as it's opening.
Chuck Norcutt
On 5/14/2014 11:11 PM, Ken Norton wrote:
No, we are describing the same thing. Sensor reads first curtain and the
camera holds back the second curtain until sufficient exposure is achieved.
If the brightness level is high enough, this point is achieved before very
much film is exposed by the first curtain. If the brightness level is low,
more and more film is exposed to the sensor before the second curtain is
released. So, the OTF metering uses the curtain as an augment to get things
moving, but dynamically moves into more and more film as the exposure is
extended.
As previously mentioned, that was an issue with the first generation OM-2
because the curtain was more center weighted than the film itself and as a
result the metering pattern changed from center weighted to averaging as
the exposure got longer.
OTF flash control varies a little bit from model to model. The first
generation OM-2 would trigger the flash even if the sync speed got too
high. The OM-2S won't fire the flash if the ambient exposure is too high
and the image would overexpose. I think the OM-4T will fire the flash even
if the exposure is too high at 1/60. The OM-3Ti is free form and lets you
do anything.
AG
On Wednesday, May 14, 2014, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
wrote:
But I will continue to maintain that the process you've described only
pertains to exposures equal to or longer than the sync speed. Continuing to
read the film surface can only be done while the shutter is fully open. If
the shutter is not fully open (speed faster than sync time) the second
curtain has already been released to form a slit with the first curtain.
The shutter speed has already been determined and further reading the film
surface makes no sense since the exposure is already committed and can no
longer be altered.
Chuck Norcutt
On 5/14/2014 4:33 PM, Ken Norton wrote:
As a result, the metering system ALWAYS begins to read the first
curtain and will continue to read the film surface until sufficient
exposure is attained. This is why the pattern changed in the first
generation OM-2. At higher shutter speeds, the OM-2 was much more
center-weighted than at longer shutter speeds.
--
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