Vivitar 500mm Preset V-500-PRE Manual - Page 8

SETTING THE STOP Your 650-1300 lens has a changeable F-stop according to the focal length. (Non-auto-Iris lens) F-stop according to the focal length is marked on the lens barrel. (Refer to the index for the distance and diaphragm scale) FOCUSING THE LENS In order to get a sharp and clear image, look through the view nder of your camera, and then rotate the focus ring which is marked "FAR NEAR" until you can see a clear image through the view nder. USING THE VIEWFINDER WITH THE TELEPHOTO LENSES The e ectiveness of di erent types of focusing screens varies with the focal length and maximum aperture of the lens. The range nder of microgrid prisms built into the ground glass do not work as well with longer focal length lenses as they do with the normal camera lens and most wide angle lenses, and may partially or full blackout the center focusing spot. When such a condition exists, focusing is best done on the ground glass portion of the viewing screen. On some SLR cameras, long telephoto lenses appear to produce a cuto image in the upper corners or along the entire upper edge of the view nder. Such viewing cuto is actually caused by the size of the camera's mirror which is more adequate for the shorter focal length lenses only. The exposed slide or negative will be una ected by this viewing de ciency. -6-