With a single lens reflex camera, the viewfinder shows the image at the largest aperture available to the lens in use. In this photo, I had my camera on full manual and set my aperture to F22, yet in the viewfinder I saw the photo at F2.8. I often use my depth of field preview button to see what the final photo will look like in terms of depth of field.
F22 at 1/10, ISO 800, 105mm lens at 105mm
