When I look through a viewfinder before I take the photo, the lens is "wide open" - at its largest possible aperture (unless the depth of field preview is used). The aperture is adjusted to whatever I set it to just before the shot.
I understand it this way: the camera tells the lens to adjust the aperture, makes a shot, and resets the aperture back to the max.
But what about manual lenses like, e.g., the Samyang 8mm FishEye f/3.5? It does not have any connection to the camera (in fact, my D5000 shows No lens attached when I mount it). I set the aperture directly on the lens and the camera has no idea about its settings. Still, the viewfinder shows the scene very brightly, even if I set f/22.
How do such lenses know when to adjust the aperture? Am I missing something?
