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HANDBOOK OF PHOTOGRAPHY 



equipment, the following material in this chapter (and a few paragraphs in the chapter 

 on Optics of Photographic Lenses) deals with the proper relations that must exist 

 between the camera and the object to be photographed, if a pleasing result is to be 

 secured from the photographer's efforts. 



Perspective. — Most photographs are attempts to represent, on a two-dimensional 

 plane, a three-dimensional scene or object. One of the photographer's most difficult 

 problems is to give the viewer of the photograph some idea of the relations in space 

 existing between the several parts of the scene or object. The appearance of the 

 several objects of a scene in respect to their relative positions and dimensions is known 

 as perspective. If a photograph shows these several objects to be in the same relative 

 position and dimension as they would appear to the eye if placed at the position of the 

 lens, the perspective of the photograph is natural. A good lens always does this: the 

 photograph made with it is natural if the eye looks at the print from the proper 

 viewpoint — but this is rarely the case. 



When one looks down a long lane of trees, those trees in the receding distance seem 

 to become shorter and shorter as the distance increases. If the photograph makes the 



Fig. 25. — Two objects of same height {AB and CD) are focused at X'Y' and X'Z' by long- 

 focus lens or at XT and XZ by short-focus lens. 



nearer trees appear taller, when compared to the distant trees, than they would appear 

 if the observer were actually looking at the scene, the perspective is exaggerated and is 

 unnatural. 



If certain conditions are fulfilled, the perspective of the photograph wUl be more 

 natural than if these conditions are not carried out. It is often said that a long-focus 

 lens produces better perspective than a short-focal-length lens. It is true that the 

 focal length of the lens enters into the problem, but the essential condition to be 

 fulfilled is that the angle subtended by the print at the eye must be equal to the angle sub- 

 tended by the object at the lens. Under this condition the perspective of the print will 

 be natural. 



The angle subtended by the print at the eye depends upon the viewing distance. 

 Since 10 in. is generally considered as normal viewing distance, when the print is held in 

 one's hands, the lens to be used is one that will focus upon the sensitive material when 

 placed 10 in. from that sensitive material — in other words, a 10-in. lens focused upon 

 infinit}'. 



All pictures made from the same viewpoint, no matter whether with a long-focal- 

 length lens or a short-focal-length lens, will have the same perspective. The short- 

 focal-length lens may include a wider field of view, and a given object will be smaller 

 than when made with the long lens, but if the fields of view of the final prints are the 

 same and if the relative heights of two objects in the two prints are measured, they 

 will be found to be the same. 



In Fig. 25, AB and CD are two images of equal height but one is closer to the 

 camera lens than the other. A short-focal-length lens will focus these images in the 

 plane XYZ. Object AB will have a height on the image plane of XY, and object 



