-----Original Message-----
From: Ken Norton <kenorton@xxxxxxxxxx>
>The IS-3 has a sensor in the bottom of the mirror box similar to our OM's.
>I looked through every page of documentation and didn't read anything about
>this sensor or OTF metering of any kind. What is it, and what does it do?
>
>Ken Norton
>
I do not know about the IS-3, but you will encounter this in virtually all
modern AF SLRs. Metering off the viewing screen is getting rare. Most modern
SLRs use a mirror that passes part of the light through the main mirror off
a second mirror to AF and/or metering sensors in the floor of the mirror
box. The OM-2S and OM-4 use this system. Very few meter OTF except for TTL
flash. Some older MF SLRs have a sensor in the side of the mirror box that
is usually for TTL flash OTF. From what I know, you just about have enough
fingers on one hand to count the cameras that measure ambient exposure OTF,
and most are Olympus. The Pentax LX is one example from the other
manufacturers. The Minolta X-700 has a unique system that takes a second
reading after the diaphragm closes and adjusts the exposure to compensate.
It is not OTF, but closer than the usual system to actual taking conditions.
Doug
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