In a message dated 99-05-12 21:52:51 EDT, you (Chuck Norcutt) write:
> Apart from the pin to stop the lens down to taking aperture, there is
> only one other pin. It doesn't matter whether the lens aperture range
> is from 1.4-16 or 5-32; that pin seems to move through the same total
> arc when shifting any lens through its full aperture range. Much to my
> greater surprise, my T-mount (which I thought was 1000assive) also
> moves the aperture pin all the way to "I'm wide open".
>
> I guess I have to go with Paul's statement of relative aperture but I'm
> not comfortable yet that I really understand the mechanism.
>
The metering is done with the aperture wide open and if the aperture is set
at wide open then the exposure will be correct. If you stop the lens down
one stop, for metering purposes, since all OMs have open aperture metering
(as opposed to stop down), the camera would still register the same amount of
light as for wide open aperture. So, the aperture lever tells the camera that
the aperture is stopped down one stop and you have to double the time the
shutter is open. And so forth for stopping down more. It doesn't matter if
the lens is an f/11 or f/1.2 as the camera measures the light at full
aperture and sets (or you set) the shutter speed accordingly. As for a T
mount adapter, it's always wide open, thus telling the camera not to bias the
shutter speed at all. If you stop down the T mount accessory, because this is
a manual exposure lens, the camera sets the shutter speed again without any
bias, still thinking its wide open, but setting the correct exposure. I hope
this is less confusing than when I reread it for typos.
Warren
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