LOW-POWER PHOTOMICROGRAPHY 



133 



TRANSPARENT OBJECTS 



Illumination by Diffused Light. Transparent objects 

 may be very evenly illuminated by the simple apparatus de- 

 scribed on page 128, and no difficulties arise beyond those 

 already mentioned. Exposures required with two metal- 

 filament lamps of 32 c. p. on a plate whose speed is about 

 200 H.D. (moderately fast), for an ordinary transparent 

 preparation of an entire insect, are only a iew seconds 

 one to five. 



Direct, instead of reflected light, can also be used, if 

 a ground-glass diffusing screen is placed between the lamp 

 and object, but the ground glass causes considerable loss 

 of light, and possibly slight lack of definition in the photo- 

 graph. Plate 14. A is an example taken in this way. 



Illumination by Means of a Condenser. The above 

 methods of illumination are not sufficiently intense for 

 thick or dark-coloured preparations, and it is best to 

 concentrate the light through the object by means of a 

 condenser. The condensers fitted to projection lanterns 

 are usually quite good enough, and Fig. 43 shows dia- 



Fig. 43 



ILLUMINATION OF TRANSPARENT OBJECTS 



mmatically how the apparatus should be set up, and 

 he light managed. The cameras shown at Figs. 1 and 2 

 can be conveniently arranged for the purpose. An object 

 rrier is made out of a piece of blackened board, in the 

 ntre of which a hole 1J" in diameter is drilled. Two 

 ieces of clock-spring are screwed to the carrier to hold 

 the object slide across the aperture, and it is attached to 

 a suitable block sliding on the baseboard. 



