>When you cross-mount like that, the camera has no way of >knowing what aperture the lens is set to. To get around this, >you have to meter the way it was done before the F: by setting >the lens to the taking aperture to meter. This is done by >actuating the depth of field preview. > >In short: those lenses will only meter properly when the depth >of field button is depressed.
You were OK up to this point. First prior to the F, Nikon cameras were rangefinder models that did not view through the lens except when using add on reflex mirror adapters and telephoto lenses. There was no DOF feature. The lenses were just preset to the desired aperture. Nothing was automatically stopped down. Other camera makers, like Exakta, were making reflex models long before Nikon and they did have ways to stop down the lens prior to fully pressing the shutter release. In the case of non-Nikon compatible lenses that used an adapter on a Nikon body, there is no linkage to the DOF preview lever so you had to manually stop down the lens to take the photo. Since this would darken the view making focusing difficult, you would focus with the lens wide open and then stop down the lens.
However I'm not aware of any Olympus to F adapters and if there was it would probably need a built in element to focus to ∞.