8 NATURE AND THE CAMERA 



On the subject of telephoto lenses we must confine 

 ourselves to their practical use. The telephoto is an 

 attachment which is used in connection with an- 

 other lens. It is placed back of the lens and enlarges 

 according to the scale marked on the barrel. As the 

 magnification increases, so is the necessary exposure 

 lengthened, for which reason it will be seen that for 

 instantaneous work a magnification of, say, lo diam- 

 eters would be out of the question. With the 

 Bausch & Lomb hand-camera telephoto attachment 

 fitted to the plastigmat lens, exposures of one hun- 

 dredth part of a second may be made if conditions 

 are very favorable and the magnification is not more 

 than about 2j^ or 3 diameters. Of course such a 

 plate must be developed carefully. With an expo- 

 sure of a twenty-fifth of a second, excellent results 

 can be obtained in bright light. The high-power 

 telephoto lens is only useful when the object to be 

 photographed is still enough to allow of a time 

 exposure. When using a telephoto lens with a hand- 

 camera be careful to hold the camera firmly : the least 

 vibration will ruin the picture. 



The tripod, though not a very important part of 

 the outfit, should be selected with care. Be sure to 

 have one that is sufficiently rigid; the legs should 

 telescope and the top be large enough to give the 

 necessary support for the camera. Be sure also that 

 the legs are well separated at the top ; that is to say. 



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