Abstract
The lenses used for the projection of both lantern slides and motion pictures are unique in the realm of optical instruments in their apparent insusceptibility to marked improvement. Within the last fifty years no kind of lens or other optical instrument has failed to receive the meticulous scrutiny of experienced and ingenious designers with a result which is a record of more or less continuous improvement. In projection lenses, on the other hand, there are two standard types which, although one of them is almost as old as photography and the other is beginning to assume an air of respectable old age, appear to meet the requirements of all kinds of projection in a fashion so satisfactory that noteworthy improvements have seemed to have been impossible. The records show not more than seven or eight patents granted on lenses said to be designed for projection and many of these admit reduction of cost rather than improved performance to have been the principal object of the inyention.
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