88 



HANDBOOK OF PHOTOGRAPHY 



The base of the Zeiss range finder is approximately 4 in. The field of view of the 

 red image is reduced in size so that only the part of the scene to be reproduced with 

 maximum sharpness is visible. 



The following notes on range finders are taken from the Zeiss Ikon bulletin "Con- 

 tax Photography." 



The simplest form of range finder comprises merely two mirrors, one fixed in 

 position and the other variable (see Fig. 21). Since "the full distance range between 

 infinity and about 3 ft. only involves a movement of the movable mirror through some 



Eye 



Glcfss pencil - 

 w/fh sem/'-Q 

 mirror an^ 

 reflecfincf prism 



Circular wedges 

 Fig. 20. — Rotating-wedge range finder. 



Fixed __^ 



Fig. 21. — Simple two-mirror range finder. 



Fig. 22. — Rotating-wedge type of range finder. 



3° which must be linked up with a movement of the focusing mount of the lens 

 through 140°, ... a small error in the mirror will involve a considerable error in the 

 focusing. 



"A very considerable advance on this construction is reached in the rotating- 

 wedge distance meter. In this instrument, a range of focusing distances between 

 infinity and 3 feet involves a revolution of the two wedges through 90°, so that a gain 

 in accuracy is reached, together with a comparative immunity from mechanical 

 breakdown and damage through shock. 



"A further gain which the wedge principle introduces is that the base distance can 

 be made of a solid glass pencil, one end of which is semi-gilded. This, though valuable, 



