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Figure 1-16.Formation of an image by a lens
Figure 1-19 Image Size and Coverage as Compared to the Lens Focal Length

Photography (Basic) - Introduction to photography and other graphic techniques
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incorporated in a single circular piece of glass (fig. 1-16). CHARACTERISTICS OF LENSES There are several factors that must be included when you are considering the characteristics of lenses. To perform  well  as  a  Navy  photographer,  you  must recognize the effect of these lens characteristics. Realize also that it is the recognition and use of these various lens  features  and/or  qualities  that  can  make  the difference between good and poor photography. You must  learn  to  recognize  the  photographic  effect  of  these characteristics and be able to apply them to produce top quality  photography.  Finally,  you  must  learn  how  some of the lens characteristics may limit photographic quality  or  operational  capability. Lens  Focal  Length In photography, lens focal length is the distance between the optical center of a lens and the focal plane (film plane) of the camera when the lens is focused at infinity (fig. 1-17). To understand this definition, you must fully understand the terms  focal plane, optical center,  and  infinity. Figure 1-17.–Focal plane and optical center. Figure 1-18.–Effects of lens-to-subject distance on light rays. Focal plane-The surface (plane) on which an image transmitted by a lens is brought to sharp focus; the surface or area at the back of the camera occupied by the film. Optical center-The optical center of a lens is a point, usually (although not always) within a lens, at which the rays of light from two different sources entering the lens are assumed to cross. Infinity-This term is not easily described. When light is reflected from the point of an object, the closer the point is to the lens, the greater is the angle of the spread of light rays from the object (fig. 1-18). As the 1-13







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