92 



HANDBOOK OF PHOTOGRAPHY 



it will be necessary to focus the camera on a plane somewhat closer than 25 ft. for a 

 given aperture.^ 



Universal Depth-of-field Table. — In the following table (Eastman Kodak) the data 

 are figured for a circle of confusion such that the angle between two lines connecting 

 the edges of the circle with the optical center of the lens is 2 min. of arc. This amounts 

 to a circle whose diameter is approximately Mooo of the focal length of the lens. In 

 such a table the circles of confusion are large for large prints and small for small prints. 



Table III.— Universal Depth-of-field Table^ 



1 Computed for criti"ally sharp definition, for fine detail. Where fine detail is not concerned, as in portraiture, the depth 

 is effectively greater. This table applies only to normal lens equipment, not to wide-angle, long-focus, or tele-photo lenses. 



The obvious use for a scale or indicator showing depth of focus is to determine 

 the nearest and most distant planes which will be in focus when the lens is accurately 

 focused upon a certain plane. But the indicator may be used in other ways. As an 

 example suppose that it is desirable to bring both a near and a far object into focus. 

 Which shall one focus upon, the near object or the far object? 



Suppose an object is 15 ft. from a camera which has a lens of 2-in. focal length. 

 At the same time, an object at infinity must be in focus. Such a lens, focused at 

 15 ft. and working at//9, will focus all objects between 9J^ and 35 ft. with good sharp- 

 ness. But the distant object is farther away and will not be sharp. If, however, 

 the lens is focused upon a plane 26 ft. distant, all objects between infinity and 12.6 ft. 

 will be in focus. Therefore the camera should not be focused upon either the near 

 object or the distant object but somewhere between. 



Other Accessories. — Discussion of filters, diffusion disks, accessory supplementary 

 lenses, plates, and films will be found in several other chapters of this book. 



Other accessories used by the well-equipped photographer include tripods, cut- 

 film holders, film and plate adapters, etc. 



' Gordon, Alfred, Depth of Focus in a Nutshell, Am. Phot., February, 1937, p. 112 (how to make 

 scales and charts); and Martin, F. T., Scale for Indicating Exposures When Bellows is Extended, 

 Am. Phot.. January, 1938, p. 38. 



