EXPOSURE.
At this stage of your photographic career you should learn to properly expose the film, then to develop it. When you are proficient in these rudimentary principles, it will be time to take up the simpler methods of printing, after which you will be instrudted in the more artistic side of the work.
In speaking of glass plates one refers to the emulsion which is coated on the glass as the "film." In case of Eastman's Non-Curling Film the entire product is so light that the whole substance is referred to as "film." In reality, however, there is a transparent base taking the place of the glass. Upon this the sensitive emulsion is coated. We then have a prod uct which is similar to a glass plate, except that it is light, thin, non-break able and rollable. The emulsion is the same in each case, the difference being entirely in the support.
Cartridge Films, however, on account of the black paper backing, do not retie& light from the back to the surface, and, therefore, are almost entirely free from halation, a defe6t which is found very largely in all glass plates unless they are specially prepared. This freedom from halation gives film a far greater latitude in exposure than can be given with plates, and especially adapts it to the conditions of harsh lighting under which the amateur ordinarily works. Everything else being equal, films will, there fore, give better average results than can be secured on glass plates.
A negative is made by the action of light on the silver salts in the emulsion with which the film is coated. Light colored objects retie& strong rays of light and they affedt the silver salts the most. If there is a clear
sky the rays of light from it will make the sky in the negative opaque or nearly so ; the rays reflected through the lens from a white house will be almost as strong as those from the sky ; the rays from the red brick chimney will affect the negative much less, while so little light comes from the heavily shaded veranda that the negative is hardly affected in this part. We have in the negative, therefore, a record of lights and shadows as we see them, but all reversed. When these are again reversed by making the print, we have them as we see them, for, as in grammar, two negatives make an affirmative, i, e., a positive.
A certain amount of light must strike the film in order to make a neg ative of proper density. We make a snap-shot out of doors on a bright day in one-fiftieth of a second. If we wish to take a pi&ure indoors on the same day, we must give from two seconds to several minutes, according to the amount of light coming through the windows and according to the color of the walls. If the latter are light in color, the exposure will be much shorter than if they are dark, because they reflect more light. You must have exposure enough, but not too much. You cannot make a snap-shot in-doors, neither can you give a long time exposure out-doors on a bright day without ruining the negative ; you must give approximately the correct exposure. But, fortunately, film is so made as to give quite a wide latitude of exposure. The length of exposure depends first of all upon the intensity of the light.