276 Botanical Microtechnique 



of such size that lantern sHdes may be made by contact, or that 

 contact prints will be ot ihc correct size for publication in a journal. 

 ^Vider use of the fine-grain methods of miniature photography will 

 promote the use of excellent objectives of comparatively low magnifi- 

 cation, large field, and good resolving power. Examples are the Bausch 

 and Lomb oil immersion, 40x> N.A. 1.00, and several makes of 

 oil-immersion objectives, with magnifications of 60 to 65 Xj N.A. from 

 1.30 to 1.40. 



The sequence of operations leading uj) to making the exposme 

 will now be described. It will be assumed that the slide, all lenses, 

 the mirror, and the filters are perfectly clean, and that all units are 

 firmly fastened in place. The procedure \aries \vith the type of il- 

 limiination beino used. 



When using an ordinary mazda bulb and a sheet of groiuid glass 

 or grainless opal glass the operations are as follows: 



1. Locate and focus the object as in visual study. 



2. Place a thin wedge of black paper against the diffusion glass, 

 and focus the condenser until the pajjer marker is in focus sinud- 

 taneously with the specimen. Remove the marker. If ground glass is 

 used, the grain of the glass will be visible, and the condenser must 

 be displaced slightly to eliminate this grain. 



3. Remove the ocidar and adjust the substage diaphragm uniil 

 the back of the objective is just filled with light. 



4. Replace the ocular, bring the camera into position, and adjust 

 the angle of the mirror luitil the illumination on the focusing screen 

 is centered. Slight readjustment of the substage condenser may be 

 necessary to obtain uniform intensit) over the illiuninated field. 



5. Focus the image sharply on the focusing screen and make the 

 exposure. 



The use of the foregoing eciuipnuiii ami [jrocedure may be re- 

 garded as amateur photomicrography, Avhich ne\ertheless alfords 

 valuable training and may yield results that meet some needs. 



For serious and critical work, the lamp sliould lia\e a concen- 

 trated filament bull), a condenser system of one or more components, 

 and an iris diaphragm. 



Two systems of illumination are j)Ossible with suitable lamps. 

 Critical illiunination is obtained when the condenser system focuses 

 the incandescent light source (filament) u|)()ii the j)lane ol the 

 specimen cjn the stage. Ihis superimposed fdament image nuist be 

 of adequate area to cover the field of the objective and must be of 



