On Thu, 23 Oct 2003, Winsor Crosby wrote:
> That astounded me and I went back to Gary's lens test page and sure
> enough the differences occurred even wide open. I know Gary was very
> careful in doing his tests, so I was wondering what other mechanism
> could be causing the softer results with the OM1. Maybe Olympus did
> some shutter refinements that damped things better when they designed
> the OM4? Or is it the aperture activation lever inside the camera
> itself? Less of a problem perhaps on an electronically activated
> aperture?
On all OM's the aperture stop-down mechanism is triggered by the upward
force of the mirror springs. Even on the OM-1 when the mirror is locked
up the spring mechanism still operates so that the aperture is closed. The
amount of force and movement is constant regardless of the lens and aperture
used. The diaphragm mechanism in each lens will control the amount of
movement needed for the selected lens/aperture combination. When mirror
pre-fire is used, all this mechanical action occurs well before the shutter
opens. That's where the benefit of the pre-fire comes in. Simply keeping
the mirror raised as in the OM-1 doesn't stop any of that vibration. Now
electronically activated apertures don't have any of these mechanical linkages
so there may be less benefit to aperture pre-fire.
-mark
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