Dear list,
"Skip Williams" <skipwilliamsom@xxxxxxxxxxx> wrote:
<< the camera likes to have film in it to do the OTF metering. Metering
off the pressure plate will often give erratic readings when running through
an OTF-automatic metering cycle of the whole shutter speed range. >>
Right, now the question:
Does the camera measure the reflectivity of the film surface when it does the
OTF cycle? I wondered about this since I read about OTF in about 1981. Films
have different surface colours and possibly reflectivities, don't they?
I wondered if:
a. there is no compensation, which I thought maybe unlikely - how about if
someone brings out a new film that is much lighter or darker in colour?
or:
b. maybe the camera measures the change in the silicon light cell reading as
the patterned first shutter blind moves away and the film comes into view.
This would fall off in a straight line if the film was less reflective than
the shutter blind, for instance (if the incident light didn't change). The
camera would then 'know' the reflectivity of the film, and then do the actual
OTF measurement when the shutter is fully open, for the slower shutter speeds
of course. ... ?
The other thing that marvelled me was how the camera can act _so_ quickly
during OTF flash metering to cut off a flashgun whose flash duration is
1/1000 second or even much less. Stunning really - that made me think, "These
guys are _really_ clever."
As an addition, in OTF flash, I guess the camera can't get any idea of the
reflectivity of the film beforehand, because before the flash actually fires,
it might be dark!
Any answers anyone?
Kind regards,
Dave Bellamy.
http://members.aol.com/synthchap/
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