232 PHOTO-MICROGRAPHY [CH. VIII 



Figs. 190-191. Fine tint, half-tone reproductions of photo-micrographs of sec- 

 tions made by Mrs. Gage, to show the possibilities of photo-micrography with pho- 

 tographic objectives and with low microscopic objectives without a projection ocular. 



1. Frontal section of the head of a large red Diemyctylus viridescens {red 

 newt) at the level of the portae of the brain, magnified 10 diameters. Negative 

 made with a Gundlach perigraphic objective of about go vim. equivalent focus. 



2. Frontal section of a larval Diemyctylus about 10 millimeters in length. 

 Negative made with a Winkel objective of 22 millimeters equivalent focus ; no 

 ocular. Magnified 50 diameters. {Mrs. Susanna Phelps Gage, the Wilder 

 Quarter Century Book). 



tained. If it does not remain in focus, something is faulty. When 

 the image remains sharp after focusing make the exposure. From 20 

 to 60 seconds will usually be sufficient time with medium plates and 

 the light as described. If a color screen is used it will require 40-300 

 seconds, i. e., 2 to 5 times as long, for a proper exposure (§ 359). 



B. Photog7-aphing with a Projection Ocular. — If the object is small 

 enough to be included in the field of a projection ocular (Fig. 185) use 

 that for making the negative as follows : Swing the camera around so 

 that it will leave the microscope free. Use an ordinary ocular, focus 

 and light the object, then insert a projection ocular in place of the or- 

 dinary one, and swing the camera back over the microscope. It is not 

 necessary to use an ordinary ocular for the first focusing, but as its 

 field is larger it is easier to find the part to be photographed. The 

 first step is then to focus the diaphragm of the projection ocular 

 sharply on the focusing screen. Bring the camera up close to the mi- 

 croscope and then screw out the eye-lens of the ocular a short distance. 

 Observe the circle of light on the focusing screen to see if its edges are 

 perfectly sharp. If not, continue to screw out the eye lens until it is. 

 If it cannot be made sharp hy screwing it out reverse the operation. 

 Unless the edge of the light circle, i. e. , the diaphragm of the ocular, 

 is sharp, the resulting picture will not be satisfactory. 



It should be stated that for the x 2 projection ocular the bellows 

 of the camera must be extended about 30 or 40 centimeters or the 

 diaphragm cannot be satisfactorily focused on the screen. The X 4 

 projection ocular can be focused with the bellows much shorter. For 

 either projection ocular the screen distance can be extended almost 

 indefinitely. 



When the diaphragm is sharply focused on the screen, the micro- 

 scope is focused as though no ocular were present, that is, first with the 

 unaided eye then with the focusing glass. The exposure is also made 

 in the same way, although one must have regard to the greater mag- 



