[stunsworth]

Mark, there's no automatic linkage between the camera and the lens. So as you stop down the lens the aperture size changes and the image seen though the viewfinder changes.

Typically what I'd do is focus with the lens wide open and then stop down the lens immediately before firing the shutter. After a while it becomes second nature to know how far to turn the aperture ring without taking your eye away from the camera.

I've taken thousands of images using this method with various Canon dSLRs.