142 Methods in Plant Histology 



If a negative is harsh and shows too much contrast, hold it closer to 

 the light and shorten the exposure; if weak and lacking in contrast, 

 hold it farther away and increase the time of exposure. 



2. Reducing and Enlarging. If a slide is to be made from a 4X5 

 or larger negative, there must be a reduction. A camera is necessary. 

 A 3|X4} camera is large enough. If any larger size is used, the 

 plate-holder must be " kitted " down to 3JX4, the standard size 

 of lantern slides in America. In using the larger cameras, mark 

 upon the ground glass the exact size and location of the lantern- 

 slide plate. Fasten the negative in some convenient place where 

 the light may shine through it: diffuse daylight is good. Then 

 arrange the camera just as in taking any ordinary picture. The 

 board shown in Fig. 25 will be just as useful in making lantern slides 

 as in making photomicrographs. At one end of the board fasten a 

 frame which will hold an 8 X 10 negative and also hold kits for smaller 

 negatives (Fig. 25, B and C). The long slot in the board will allow 

 the camera to be fastened at the proper distance. If buildings, trees, 

 or shadows are in the way, tilt the board so as to have a clear sky for 

 a background. 



Be very careful in focusing; it is best to examine, with a pocket 

 lens, the image on the ground glass. In general, use a rather small 

 stop, F 16 or even F 32. If reducing from an average 5X7 negative, 

 in good daylight, with an F 16 stop, try 3 or 4 seconds. If enlarging 

 from a negative somewhat smaller than a lantern slide, try 8 or 10 

 seconds. Other things being equal, the best lantern slides are made 

 by reduction from larger negatives and the poorest by enlargement 

 from smaller negatives. 



3. Copying Illustrations. It is often desirable to get lantern 

 slides from photographs, maps, or pictures in books. Here, it is 

 necessary to make a negative and then make the lantern slide from the 

 negative. In such cases make a 3| X4 negative and print the lantern 

 slide by contact. A lantern-slide plate is good for such copying. 

 The exposure will depend upon the light, the character of the print, 

 and the amount of reduction or enlargement. Other things being 

 equal, the exposure will always be longer in case of enlargement than 

 in case of reduction. If an average 5X7 photograph is to be copied 



