On Sep 11, 2009, at 13:38, Desjardins, Steve wrote:
It was, essentially, a little doohickey inside the body end of the
lens mount that pressed a tiny pin on the older lenses that would
make the lens stop down to chosen f stop. It went away when Pentax
ate from the tree of digital knowledge, but many still await its
return.
bzzt!
It was a lever on the body which would interact with a lever on the
lens (K-M series automatic lenses) so that the camera body would know:
"hey, this lens is now stopped down to such-and-such a stop" while
allowing the aperture to remain all the way open. The light meter
would compensate as if there was less light coming in so that you'd
know the exposure was set correctly.
When the photo is/was taken, the other thingie which has been holding
the aperture all the way open would drop and the lens would stop down
to the set value - shutter opens, shutter closes, aperture again pops
all the way open.
This ability (to "just know" what aperture the K or M lens is set to)
is not in the digital SLR bodies. If you have a "non-A" lens, and you
want to shoot at something other than wide open, you have to use
manual mode and "the green button" to physically stop down the lens,
take a light reading WITH THE APERTURE STOPPED DOWN, and then pop the
aperture wide open to let you focus, compose, etc.
I may have some specifics wrong, but that is *basically* it.
-Charles
--
Charles Robinson - [email protected]
Minneapolis, MN
http://charles.robinsontwins.org
http://www.facebook.com/charles.robinson
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