HYPERFOCAL DISTANCE.–The hyperfocaldistance of a lens is the distance from the optical centerof the lens to the nearest point in acceptably sharp focuswhen the lens, at a given f/stop, is focused at infinity. Inother words, when a lens is focused at infinity, thedistance from the lens beyond which all objects arerendered in acceptably sharp focus is the hyperfocaldistance. For example, when a 155mm lens is set at f/2.8and focused at infinity, objects from 572 feet to infinityare in acceptably sharp focus. The hyperfocal distancetherefore is 572 feet.The following equation is used to find hyperfocaldistance:F^{2}H =f x CWhere:H = hyperfocal distanceF = focal length of lensf= f/stop settingC= diameter of circle of confusionF and C must be in themillimeters, and so forth.same units, inches,NOTE: 1 inch is equal to 25.4mm.Where:F= 155mm (6.1 inches)f= 2.8C= 0.05 (0.002 inches)Then:H =6 .1^{2}2.8 x 0.002= 6650 inches = 554 feetThus the hyperfocal distance for this lens set at f/2.8 is554 feet.Hyperfocal distance depends on the focal length ofthe lens, the f/stop being used, and the permissible circleof confusion. Hyperfocal distance is needed to use themaximum depth of field of a lens. To find the depth offield, you must first determine the hyperfocal distance.By focusing a lens at its hyperfocal distance, you causethe depth of field to be about one half of the hyperfocaldistance to infinity.ND =H x DH + DDEPTH OF FIELD.–Depth of field is the distancefrom the nearest point of acceptably sharp focus to thefarthest point of acceptably sharp focus of a scene beingphotographed Because most subjects exist in more thanone plane and have depth, it is important in photographyto have an area in which more than just a narrow, verticalplane appears sharp. Depth of field depends on the focallength of a lens, the lens f/top, the distance at which thelens is focused, and the size of the circle of confusion.Depth of field is greater with a short-focal-lengthlens than with a long-focal-length lens. It increases asthe lens opening or aperture is decreased. When a lensis focused on a short distance, the depth of field is alsoshort. When the distance is increased, the depth of fieldincreases. For this reason, it is important to focus moreaccurately for pictures of nearby objects than fordistance objects. Accurate focus is also essential whenusing a large lens opening. When enlargements are madefrom a negative, focusing must be extremely accuratebecause any unsharpness in the negative is greatlymagnified.When a lens is focused at infinity, the hyperfocaldistance of that lens is defined as the near limit of thedepth of field, while infinity is the far distance. Whenthe lens is focused on the hyperfocal distance, the depthof field is from about one half of that distance to infinity.Many photographers actually waste depth of fieldwithout even realizing it. When you want MAXIMUMdepth of field in your pictures, focus your lens on thehyperfocal distance for the f/stop being used, NOT onyour subject which of course would be farther away thanthe hyperfocal distance. When this is done, depth of fieldruns from about one half of the hyperfocal distance toinfinity.There are many times when you want to know howmuch depth of field can be obtained with a given f/stop.The image in the camera viewing system may be too dimto see when the lens is stopped down. Under theseconditions, some method other than sight must be usedto determine depth of field. Depth of field can be workedout mathematically.The distance, as measured from the lens, to thenearest point that is acceptably sharp (the near distance)is as follows:The distance, as measured from the lens, to the farthestpoint that is acceptably sharp (the far distance) is asfollows:1-25