Camera Lens Parts: Depth-of-Field Scale
Among the various camera lens parts, you will find the Depth-of-Field (DOF) Scale, between the aperture ring and the focal length ring. The DOF Scale gives you a creative control over manipulating the area of focus in your photos. You can selectively make an area in the image sharper or achieve an overall sharpness for the entire photo or something in between.
DOF Scale does not in any way manipulate the properties of the lens, but it determines the range of sharpness of different objects across distances when the image is reproduced in print. You will determine the required setting on the DOF scale by taking into consideration the distance you are from the object, the focal length of your lens, the size of aperture and the format size. Based on these parameters, people have devised various formulas to determine the DOF in different situations.
Usually there is an increment in the DOF Scale when you decrease the aperture by increasing the "f-stop" number. Sometimes Telephoto lenses are used to limit the DOF, especially when taking portraits, where you want only one object in sharp focus. So, depending on the type of sharpness you need for the different objects in your photo you will be adjusting the DOF scale.