198 



PHOTO MICROGRAPHY. 



[CH. VIII. 



carefully, however. This label should contain as far as possible, the 

 following information : (1) Kind of plate ; (2) Time of exposure ; (3) 

 Light used ; (4) Objective; (5) Ocular ; (6) Magnification ; (7) Name 

 of object and number of preparation from which taken ; (8) Date of 

 making the negative. 



Fig. 154. Tripod magnifier. This serves fairly well 

 as a focusing glass, but is inferior to the one shown in 

 Fig- A53- 



§ 339. Low Microscopic Objectives. — Mi- 

 croscopic objectives of 35 mm. and greater focal 

 length may be attached to the camera directly 

 after the manner of a photographic objective if 

 one has a plate made with the proper screw for 

 the objective. The only difficulty is in focusing 

 the object properly. If one has the special stand 

 made by the Bausch and L,omb Optical Co., or something equivalent so 

 that the object may be moved with a fine screw, the focusing can be 

 well done. Such an arrangement is also very convenient in using the 

 photographic objectives (Figs. 151-152) and the apochromatic objec- 

 tives of 35 and 70 mm. focus made by Zeiss. 



Fig. 155. Engraving glass to serve as 

 a bull's-eye condenser. [From the 

 Bausch and Lomb Optical Co. ). 



$ 340. Photo-Micrographs of 

 20 to 50 Diameters. — For these, 

 low objectives are used (35 mm. to 

 20 mm. focus). They are attached 

 to the camera as described in § 339 

 or a microscope is used. If the 

 microscope is used the object is 

 placed on the stage and focused in 

 the usual wav. The mirror is pref- 

 erably removed or swung aside and the lamp and bull's eye mutually 

 arranged to give an image of the flame as described in § 335. If the 

 object is small the achromatic condenser may be used (See § 342)01- 

 one of the Steinheil magnifiers. When the light is satisfactory as seen 

 through an ordinary ocular, remove the ocular. 



(A) Photographing- without an Ocular. -After the removal of the 

 ocular put in the end of the tube a lining of black velvet to avoid re- 

 flections. Connect the microscope with the camera, making a light 

 tight joint and focus the image on the focusing screen. It will be 



