HYPERFOCAL  DISTANCE.–The    hyperfocal distance of a lens is the distance from the optical center of the lens to the nearest point in acceptably sharp focus when the lens, at a given f/stop, is focused at infinity. In other words, when a lens is focused at infinity, the distance  from  the  lens  beyond  which  all  objects  are rendered in acceptably sharp focus is the hyperfocal distance. For example, when a 155mm lens is set at f/2.8 and focused at infinity, objects from 572 feet to infinity are in acceptably sharp focus. The hyperfocal distance therefore is 572 feet. The following equation is used to find hyperfocal distance: F² H   = f  x  C Where: H   =  hyperfocal  distance F    = focal length of lens f = f/stop setting C = diameter of circle of confusion F  and  C  must  be  in  the millimeters,  and  so  forth. same   units,   inches, NOTE: 1 inch is equal to 25.4mm. Where: F = 155mm (6.1 inches) f =   2.8 C =  0.05 (0.002 inches) Then: H    = 6 . 1² 2.8  x  0.002 = 6650 inches = 554 feet Thus the hyperfocal distance for this lens set at f/2.8 is 554 feet. Hyperfocal distance depends on the focal length of the lens, the f/stop being used, and the permissible circle of confusion. Hyperfocal distance is needed to use the maximum depth of field of a lens. To find the depth of field, you must first determine the hyperfocal distance. By focusing a lens at its hyperfocal distance, you cause the depth of field to be about one half of the hyperfocal distance  to  infinity. ND  = H  x  D H  +  D DEPTH OF FIELD.–Depth of field is the distance from the nearest point of acceptably sharp focus to the farthest point of acceptably sharp focus of a scene being photographed  Because  most  subjects  exist  in  more  than one plane and have depth, it is important in photography to have an area in which more than just a narrow, vertical plane appears sharp. Depth of field depends on the focal length of a lens, the lens f/top, the distance at which the lens is focused, and the size of the circle of confusion. Depth of field is greater with a short-focal-length lens than with a long-focal-length lens. It increases as the lens opening or aperture is decreased. When a lens is focused on a short distance, the depth of field is also short. When the distance is increased, the depth of field increases. For this reason, it is important to focus more accurately for pictures of nearby objects than for distance objects. Accurate focus is also essential when using a large lens opening. When enlargements are made from a negative, focusing must be extremely accurate because any unsharpness in the negative is greatly magnified. When a lens is focused at infinity, the hyperfocal distance of that lens is defined as the near limit of the depth of field, while infinity is the far distance. When the lens is focused on the hyperfocal distance, the depth of field is from about one half of that distance to infinity. Many photographers actually waste depth of field without even realizing it. When you want MAXIMUM depth of field in your pictures, focus your lens on the hyperfocal distance for the f/stop being used, NOT on your subject which of course would be farther away than the hyperfocal distance. When this is done, depth of field runs from about one half of the hyperfocal distance to infinity. There are many times when you want to know how much depth of field can be obtained with a given f/stop. The image in the camera viewing system may be too dim to see when the lens is stopped down. Under these conditions, some method other than sight must be used to determine depth of field. Depth of field can be worked out  mathematically. The distance, as measured from the lens, to the nearest point that is acceptably sharp (the near distance) is as follows: The distance, as measured from the lens, to the farthest point that is acceptably sharp (the far distance) is as follows: 1-25