1 38 PHOTOMICROGRAPHY 



permit. There are one or two points to which attention 

 should be directed in this figure. The lamp is a petrol 

 vapour lamp hung on a retort stand, so that its height 

 may be adjusted. A colour screen is attached to the 

 mirror-holder by wire clips, and there is a simple arrange- 

 ment of pulleys carrying threads by which focussing is 

 carried out. A short dead-black cardboard or metal tube 

 is attached to the camera-front, and makes a light-tight 

 connection by sliding inside the tube of the microscope. 

 The camera is fixed at the front, and extends towards 

 the back, where a screw focussing arrangement is fitted. 

 The draw-tubes of the microscope are entirely removed. 



To Adjust the Light and Take the Photograph. The lamp 

 and condenser are carefully centred to the objective, 

 and the distance between them adjusted, so that an image 

 of the radiant falls across the front of the lens, and fills 

 its aperture. This can most easily be done by holding 

 a card in the position to be occupied by the lens. The 

 camera and microscope are connected light-tight, and the 

 illumination on the ground glass or white card carefully 

 examined, and any unevenness rectified by slight move- 

 ment of the lamp. The object is then placed in position, 

 roughly focussed, and the bellows extended until the 

 desired magnification is obtained. The stage is rotated 

 if necessary until the object lies in the best position in 

 regard to the plate. The diaphragm attached to the 

 condenser is then restricted until the diameter of the beam 

 of light is just suificient to cover the object. Excess of 

 light is liable to cause a mistiness over the image. Colour 

 screens, and if necessary ground glass, are put in position. 

 The object is focussed and the iris of the lens carefully 

 closed until the sharpest image is obtained, or to increase 

 depth of focus, and exposure made as previously described. 



Flare Spot is one of the difficulties encountered when 

 eyepieces are not used, and arises from reflections caused 

 by bright parts in the microscope tube. It appears as a 



