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Re: [OM] Full aperture metering, part 99...

Subject: Re: [OM] Full aperture metering, part 99...
From: Richard Ross <rhdesign@xxxxxxxxxxxxx>
Date: Fri, 14 May 1999 11:23:43 +0100
>>This is at best only partly true since the meter needs to know the maximum
>>aperture of the lens and what the lens will be stopped down to at exposure
>>time. A modern (!) manual camera like the OM1 does the metering at max
>>aperture not stopped down. Thus the teleconverter passes through a
>corrected
>>maximum aperture by offsetting the pin indicating the maximum aperture by
>the
>>right amount through to the OM body.


Nope!  The meter is reading the light transmitted *through the lens*.  So
if you add a 2x TC, the amount of light transmitted is two stops less, so
the meter reads two stops less.  The meter does *not* need to be told the
max aperture of the lens - it can tell that from the amount of light it
sees.  All it needs to know is whether or not the lens is stopped down from
maximum so it can apply the necessary correction to the reading (since at
exposure time there will be less light reaching the film if the lens is
stopped down).  There is no need for any pin offsets, and the aperture pin
on all lenses is in the same relative position.

Hope this clears it up :-)

Richard


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Richard Ross, B.Sc, Ph.D, LRPS

RH Designs - fine darkroom equipment
for the discerning photographer
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tel:  +44 (0) 1442 258111
richard@xxxxxxxxxxxxxxxxxxxxxxx

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