Photomicrography 



55 



Selection of Film Size. The equipment used in the reflex and split-beam 

 cameras just described leave no option to the user. He is limited to the 

 size, usually 35 mm, of the camera. This is, actually, no disadvantage, 

 provided fine-grain film be used. Figure 67 shows a contact print and a 

 X12.5 enlargement from such a film. The granules in the bacteria are 

 perfectly apparent in the print since the resolution of both the objective 

 and the film was adequate. The writer has taken many photographs of 

 such granules using 4- by 5-in. film and every artifice possible by the 

 method of direct-image projection. The pictures so obtained are undoubt- 

 edly slightly better. It is doubtful whether they are sufficiently better to 

 compensate for the inconvenience and effort involved. At lesser magnifi- 

 cations, 35-mm film is always adequate. Every photomicrograph in this 

 book, except Figs. 15, 16, 17, 135, and 136, were taken with the equip- 

 ment shown in Fig. 66. 



Cameras of the type used in direct-image projection usually take either 

 4- by 5-in. or 5- by 7-in. film. This film must be placed in a dark slide and 

 this, moreover, must be done in absolute darkness. For this reason, all cut 

 film sheets are notched in one corner. The sensitive surface of the film 

 is toward the user when the forefinger of the right hand (Fig. 68) rests 

 on the notches. This being established, the film is slid into the grooves 

 of the holder and the dark slide is closed. 



Glass plates coated with emulsions, which are really better in sizes 

 of 5 in. by 7 in. and larger, cannot of course be notched. An experienced 

 and sensitive finger can always tell which is the emulsion side. The be- 

 ginner had best nibble the corner 



of the plate with moist lips. The 

 emulsion adheres to the lips, the 

 glass does not. 



The dark slide (lower part of 

 Fig. 68), which must be drawn out 

 after the holder is in its grooves 

 and before the exposure is made, 

 has conventionally one side of its 

 upper margin black and the other 

 white. If the black be outermost 

 when the film has not been ex- 

 posed, and the white when it has, 

 double exposures can be avoided. 



Every film camera comes with di- 

 rections for loading film and there 

 is no reason to repeat these here. 



Selection of a Filter. One of the advantages of photographic over visual 

 observation is that the film may be made to emphasize one or more fea- 



Fig. 68. Inserting cut film into a dark 

 slide. Notice the notches under the fore- 

 finger, which vouch for the fact that the 

 film is right way around. 



