How is the camera lens focused?

In relationship to the film ( which is positioned at the focal plane), the lens can be moved backwards and forwards to focus the specific part of the scene being photographed by rotating a barrel on the lens. While the point of focus and the corresponding distance scale is usually marked on the lens, with SLR or TLR cameras that allow the photographer to view the scene through the lens the focus becomes visually obvious in the view finder.

Cameras with other viewing systems use different methods. The view camera focuses the image on a piece of ground glass that sits exactly where the film will be placed for the exposure.

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