On Fri, 4 Sep 1998 09:35:27 -0700 (PDT), Dan Lau wrote:
>Many others have already answered this question, but basically you set
>the lens to the widest aperture you want the camera (computer) to use,
>and it will stop it down from there if necessary. For example, if you
>have a 50/f1.8 lens, you can set the aperture at 1.8 and the camera will
>try to choose the fastest shutter speed to make a good exposure. If
>the fastest shutter speed is still not fast enough, it will start closing
>down the aperture, etc. So if you want a certain degree of control of
>the depth of field, you can close down the aperture and the camera will
>not open it wider than what you have set -- it will adjust the shutter
>speed to fit your chosen aperture, again, closing down from there if
>necessary.
Sorry to contradict you here, Dan, but I think you got this the wrong way
around. Until the moment you press the release button, your lens is wide
open, thus giving you a bright viewfinder image and facilitating focussing.
What happens with all OMs is that you set a stop on the lens, and the camera
will close the aperture down to that pre-selected stop right before
releasing the shutter, using one of the small levers in the lens mount. You
can do the same by pressing the DOF preview button on the lens. However,
neither the DOF button nor the lever can stop the lens down beyond the
aperture you have selected on the aperture ring. What happens in the PC is
that it does not necessarily move the lever all the way, so it can stop
between wide open and the selected value. So in your example above, you have
pre-selected the widest aperture this lens is capable of, and there is no
way for the camera to stop it down any further. Therefore, if you want to
let the program fully control your exposure, you must select the smallest
aperture your lens will allow (22 or 16 in most cases). By selecting a
larger aperture you can limit how far the program will be able to stop down,
but you can never prevent it from shooting wider open than what you
selected.
MtFbwy,
Volkhart
--
Volkhart Baumgaertner email: kyu@xxxxxxxxxxxxxxx
MausNet: @BA
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