LOW-POWER PHOTOMICROGRAPHY 



131 



diameters with a 3" lens, requires a camera extension of 

 27", whereas 5" and 7" lenses necessitate extensions of 

 45" and 6 3" respectively to obtain the same magnification. 



Fig. 42. 



VERTICAL CAMERA FOR SOLID OBJECTS 



The extension required under any circumstances is 

 calculated from the formula : 



E=FM+F 



where F = focal length of the lens 

 and M = magnification. 



