I have used a bellows some which has similar lack of
mechanical linkages. The exposure problem can be worked
around.
You open up the lens all the way (which is where the
camera expects the aperture to be.)
Once you have framed and focussed, adjust the time of
the exposure so that you get the correct exposure. Stop
down to the desired aperture. For every stop down make
an equal number of stops adjustment on other controls.
Speed is the easiest way to make the adjustment. (Two
stops down mean 4X the exposure time. Go from 1/60 ->
1/15 of a second.)
An alternative may be available with OM2n and similar
models that allow OTF auto exposure control.
I have not tried this, so can make no claims.
Some cameras have a different metering mode to take into
account the fact that the lens is not linked to the
aperture control. The C*n*n FTb is one such. I do not
know if any Oly have such, but they probably don't need
them with the OTF exposure.
Date: Thu, 23 May 2002 19:43:41 +1200
From: "Brian Swale" <bj@xxxxxxxxxxxxxxx>
Subject: [OM] ( OM ) extension tubes ; manual or automatic
Ralph wrote;
> I'm sure this is a dumb question, but here goes. What
> is the difference between manual and automatic
> extension tubes. I've looked at the pdf manual for
> both, and I'm still not clear.
As far as I know, the auto tubes contain mechanical linkages between the
lens on the one end and the camera on the other, so that the camera is
informed what aperture has been set in the lens.
Thus the user can get some indication in the view-finder what the exposure is
likely to be.
With the manual tubes (I've never handled any) I assume they are more or
less plain & simple tubes with no linkages.
HTH
Brian
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