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INTRODUCTION 5
The manufacturer naturally advertises the possibilities of his apparatus as if he expected it to be used under the most favorable conditions, and operated by men skilled in the use of optical instruments, and the results to be judged by persons of experience who do not expect the impossible.
For example, if one reads the statements concerning the projection of pictures in books, photographs, postal cards and actual objects, the impression would be very strong that the screen pictures so produced were every bit as satisfactory as those of lantern slides, and just as easily produced. In speaking with many individuals we have found the belief is very general that with the new apparatus nothing is simpler than to get good screen images of objects, pictures, etc., with all their natural colors, and that the expense of lantern slides can be wholly done away with. But we have yet to find the actual user of such apparatus who found his sanguine expectations fully realized.
Modern opaque projection is marvelous in its accomplishments, but what is gained in the use of actual objects, books, etc., is lost in the relative dimness of the screen image, in the expense and difficulty of managing the apparatus, and in the large electric current needed to give even tolerable screen images.
Judging from our observations the manufacturers have not fully realized the lack of optical and mechanical knowledge and instinct in many users of projection apparatus. Naturally, the user of the apparatus wants results, and he wants the apparatus to give the results without trouble.
Perhaps the most striking, as also it seems to us the most easily obviated defect, is, that with many parts of the apparatus, it is just as possible to insert them in the wrong position as in the right position. For example, in most of the apparatus we have examined the condenser is so mounted that it can be put with either end facing the arc lamp. So with many other parts, they can be put in a wrong position just as easily as in a right position.
In our opinion there are five fundamental rules in the production of projection apparatus that the manufacturers should follow: