In article <4ok7gg$cel@usenet.ucs.indiana.edu>, smitra@devoras.ucs.indiana.edu says... [....]

>Ok, I have a question. With the SLR's I thought what you see is
>what the film sees. Doesn't this make DOF preview redundant?

This is only (approximately) true if you are using the lens at maximum aperture. The camera does not show you the image with the diaphragm
stopped down (with greater resultant DOF), unless you close the aperture manually with a DOF preview control. The diaphragm normally stays open
for viewing and focusing on an SLR, and stops down to the selected
aperture only during exposure (when you cannot see it happen).
Hope This Helps