Abstract: A device is provided for previewing the field of view of an optical lens, for use in still, motion picture or video photography. The device includes a fixed member having an aperture therein and a movable member. The movable member adjusts the size of the aperture in the fixed member. The device further includes a spacer for spacing the user's eye away from the aperture. The fixed member includes a series of openings and the movable member carries indicia which are selectively viewable through said openings, depending on the position of the movable member. The indicia then exposed indicate the focal length of the appropriate lens to be used in order to cover the field of view represented by the selected aperture.