This lens is mounted and used with the quick return mirror fixed in the retracted position. A reverse Galileo type finder must be used and focusing is performed by measuring the distance visually. This super-wide-angle lens has a very deep depth of focus. When it is opened to maximum aperture and focused at 3 meters (approx 10 feet), the depth of focus is 1.5m (5 feet) to infinity. When the aperture is set at F/11 and the lens is focused at 1 meter (approx. 3.3 feet) the depth of focus is an extraordinary 2 feet to infinity. Construction: 9 elements in 7 groups. FEATURES: * Coating: Magenta, Purple * Diaphragm: Manual type * Minimum aperture: F/16 * Weight: 5 5/16 oz.