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214 PREPARATION OF LANTERN SLIDES [Cn. VIII
camera known as a "copying, enlarging, and reducing camera" (fig. 116-119). As seen from the picture, the objective is placed in the middle segment if lantern slides are to be made from negatives, and the negative is placed in the proper sized frame or "kit" at the end of the camera. No light then reaches the negative except on the face looking toward the light, hence there will be no trouble from reflections.
In the best form of these cameras there is a "back with revolving, rising and vertical sliding lantern-slide attachment" for printing and for making the negatives (fig. 119). The picture can be got on the plate in the exact position desired, i. e., lines of print, etc., exactly parallel with the edge of the plate. By means of a camera one can print lantern slides from the negatives before they are dry. This is sometimes a great convenience.
§331. Printing lantern slides by artificial light. — With contact printing one can use daylight or any convenient artificial light — petroleum, gas, acetylene or electric. For printing with the camera, however, it is not so easy to get the negative evenly illuminated. A good way to evenly illuminate the negative is to use a 45 degree cardboard reflector illuminated with one or two incandescent lights, preferably with frosted bulbs in a horizontal position. Mantle gas lights serve well for illuminating the cardboard. The negative is set vertically some distance from the cardboard.
The time for printing lantern slides by contact or by the aid of a camera will vary with the negative as for paper prints; much depends on the intensity of the light and on the rapidity of the plates used.
To give an example of the time required in a given case the following table is added :
The same objective with a diaphragm opening of F/8 was used for all, and the same negative was used in each case. All the plates were from the same box and the same developer was used for all, so that the only variable was the light.
1. Sky background, diffused light 10 seconds.
2. Cardboard at 45 degrees, under the sky 15 seconds.