44 ELEMENTARY PHOTO-MICROGRAPHY. 



put with the edge of the flame (not the flat) towards 

 'the condenser. The fiat side of the bull's-eye is 

 put next the flame, at its proper focal distance, 

 and with centre of lens at same height as centre of 

 flame. Having done this, the photographer's next 

 step is to look right into the lens through a pair of 

 neutral tint spectacles, and to raise or lower the 

 flame until the whole area is brilliantly illuminated. 

 If dark spots appear in the lens, it is moved 

 towards or from the flame to get a bright disc of 

 light. If this does not give the desired result, 

 raising or lowering the lens must be tried. When 

 the bull's-eye is too near the flame it will show dark 

 patches with bright line in the middle, as fig. 16, 

 and when too far away it will appear as fig. 17. 



O 



FIG. 1 6. Fio. 17. 



If focussed but not centred, a crescent of light 

 will show at one side of the bull's-eye. A little 

 experimenting will soon give the correct position, 

 and when once this is determined, make a mark on 

 the bull's-eye spindle, so that it can be removed 

 and replaced in exactly the same position, to 

 facilitate the occasional use of the lamp flame 



