2^4 PHOTO-MICROGRAPHY [CH. VIII 



\ 362a. Size of Camera. — The majority of photo-micrographs do not exceed 8 

 centimeters in diameter and are made on plates 8x 11, 10 x 13 or 13 x 18 centimeters 

 ( V4.'x4'4 in., 4x5 in., or 5x7 in.). Most of the vertical cameras are for plates not 

 exceeding 10 x 13 centimeters (4x5 in. ) but Zeiss' new form will take plates 21x21 

 centimeters (S'+xS 1 / in.). 



8 363. Work Room. — It is almost self-evident that the camera must be in 

 some place free from vibration. Frequently a basement room where the camera 

 table may rest directly on the cement floor or on a pier is an excellent situation. 

 Such a place is almost necessary for the best work with high powers. For those 

 living in cities, a time must also be chosen when there are no heavy vehicles 

 moving in the streets. For less difficult work an ordinary room in a quiet part of 

 the house or laboratory building will suffice. 



\ ^64. Arrangement and Position of the Camera and the Microscope. — For 

 much of photo-micrography a vertical camera and microscope are to be preferred 

 (Fig. 1S4). Excellent arrangements were perfected long ago, especially by the 

 French. (See Moitessier. ) 



Vertical photo-micrographic cameras are now commonly made, and by some 

 firms only vertical cameras are produced. They are exceedingly convenient, and 

 do not require so great a disarrangement of the microscope to make the picture as 

 do the horizontal ones. Van Heurck advises their use, then whenever a structure 

 is shown with especial excellence it is photographed immediately. The variation 

 in size of the picture is obtained by the objective and the projection ocular rather 

 than by length of bellows (see below Fig. 184). It must not be forgotten, how- 

 ever, that penetration varies inversely as the square of the power, and only in- 

 versely as the numerical aperture (''/, 34), consequently there is a real advantage in 

 using a low power of great aperture and a long bellows rather than an objective of 

 higher power with a short bellows. A horizontal camera is more convenient for use 

 with the electric light also (Fig. 192). 



For convenience and rapidity of work a microscope with mechanical stage is 

 very desirable. It is also an advantage to have a tube of large diameter so that 

 the field will not be too greatly restricted (Fig. 189). In some microscopes the 

 tube is removable almost to the nose-piece to avoid interfering with the size of the 

 image. The substage condenser should be movable on a rack and pinion. The 

 microscope should have a flexible pillar for work in a horizontal position. While it 

 is desirable in all cases to have the best and most convenient apparatus that is 

 made, it is not by any means necessary for the production of excellent work. A 

 simple stand with flexible pillar and good fine adjustment will answer. 



\ 365. Objectives and Oculars for Photo-Micrography. — The belief is almost 

 universal that the apochromatic objectives are most satisfactory for photography. 

 They are employed for this purpose with a special projection ocular. Two very 

 low powers are used without any ocular (Fig. 180). Some of the best work 

 that has ever been done, however, was done with achromatic objectives (work of 

 Woodward and others). One need not desist from undertaking photo-micrography 

 if he has good achromatic objectives. From a somewhat extended series of ex- 

 periments with the objectives of many makers the good modern achromatic ob- 

 jectives were found to give excellent results when used without an ocular. Most 

 of them also gave good results with projection oculars, although it must be said 

 that the best results were obtained with the apochromatic objectives and projec- 



