This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Illuminants. Photo-micrographs may be made by either daylight or any artificial light, but more uniform results will be obtained by means of artificial light, as it is not as strong as daylight - it permits of more latitude in exposure and is more even. However, one should be guided by one's own conveniences.
Daylight Illuminant. When using the microscope and camera for daylight illumination, do not place the instrument in direct sunlight. Subdued light is best, as it allows for more latitude in the exposure. Neither should you place the instrument too near the window, but close enough to obtain illumination and overcome the reflection of the division sash of the window into the mirror. Usually, working about two feet from the window will give you good illumination.
Diffusing The Light. A very good way to modify the light, if too strong, is to provide a piece of heavy cardboard, about 14 x 17 inches in size. Near one end of the cardboard cut a square opening about 10 x 12 inches. Cover this opening with fine white tissue-paper, pasting around the edges. About three or four inches from the bottom of this card, bend it at right angles to form a base for its support. The sides are braced by means of cardboard cut wedge-shape and glued into the corners. See Fig. 1, Illustration No. 122, which illustrates completely the arrangement for daylight exposure.
Artificial Light. In Fig. 2, of Illustration No. 120, is shown the use of electric light for exposing. For this purpose a 32-candle power incandescent bulb is used. In this illustration you will observe the large, white card back of the electric bulb which serves as a reflector. By means of the reflector the light is made more powerful, thus shortening the exposure. In Illustration No. 123, Fig. 3, is shown an arrangement for illuminating by gasoline vapor lamp. This class of light is used practically the same as the electric light. Fig. 4 shows the arrangement for illuminating with gaslight.
683. These different illustrations show the various forms of artificial light, and have all been tried and found to give satisfactory results. If none of these sources of illumination are available, a good kerosene lamp can be used with success, but considerably longer exposure will be required. The selection of the illuminant is entirely immaterial. You must be guided by your surroundings, and you may make use of any light at hand. The use of gaslight is, perhaps, the most convenient and easily manipulated, and it is almost universally available, as nearly every city and town has its gas supply system.
Note. Where manufactured gas is used it will be necessary to use a globe that is perforated at the base with holes about 1/4 inch in size. This supplies vents for the air and a steady illumination is secured. (See A, Fig. 3, Illustration No. 124.)
Illustration No. 122 Fig. 1, Daylight Illumination Fig. 2, Enlarging Microscopic Slides See Paragraph 681
Illustration No. 123
See Paragraph 682
Illustration No. 124
See Paragraph 684
Illustration No. 126
Focusing and Adjusting Object for Microscopic Reproduction
See Paragraph 687
685. In Figs. 2 and 3 of Illustration No. 124 is shown a horizontal arrangement of the camera and microscope for gaslight illumination. The camera is supported by a solid wooden block, which makes the camera quite rigid. When used horizontally the Abbe condenser is usually dispensed with and the bull's-eye condenser is substituted. The horizontal arrangement will be found the easiest for illuminating the slide, but aside from this the upright position will give you a more rigid support for the camera and the focusing will be much simpler and easier to adjust. In Fig. 3 of Illustration No. 124 we have the horizontal use of the microscope with the yellow screen or filter.