30 ELEMENTARY PHOTO-MICROGRAPHY. 



threaded hole in the centre to receive any low 

 power microscopic objective, as shown in fig. 7. 

 A Davis shutter, or small iris diaphragm, to " stop 

 down " will be helpful in controlling the depth 

 of focus. 



With a long tube microscope the field of view 

 is limited to a comparatively small area, and it 

 would be found difficult to see in one view even 

 the whole of such a small coin as a threepenny 

 bit, whereas by means of the adapter a five-shilling 

 piece could be covered and photographed. The 

 watch face (fig. 8), real size of dial ijin. diameter, 

 was taken to show the covering power of a 3in. 

 objective. 



To TAKE A PHOTOGRAPH SAME SIZE AS OBJECT 

 WITH AN ORDINARY PHOTOGRAPHIC LENS. 



Extend the camera so that the ground-glass 

 screen from the focal centre of lens shall be twice 

 the focus of lens, whatever that may happen to 

 be, and put the object to be photographed at 

 exactly the same distance in front of the lens. 



The distance, therefore, between object and 

 image will be four times the focus, with lens in 

 centre. 



For example, suppose focus of lens be 5 Jin., 

 the image would be nin. behind the lens, and the 

 object nin. in front. Butterflies, spiders, shells, 



