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SOME FACTS CONCERNING PROJECTION LENSES
Wilbur B. Rayton*
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 invention.
The two types of lenses referred to are the Petzval portrait lens and the triplet construction due to H. Dennis Taylor. The first was announced in 1840, the second in 1895. The general type of the first is shown in Fig. 1 and of the second in Fig. 2. It is of no interest here to record the details of construction of these lenses and in fact impossible, for probably every manufacturer uses formulae for his lenses peculiar to himself none of which are exactly like the original Petzval construction or like any of the originally published triplets of Taylor. Within a comparatively few years after its birth the original Petzval form was subjected to modification by Dallmeyer, Voigtlander, and Zincke-Sommer. These modifications have become classic lens forms but there have been scores of other modifications which have never been honored by special mention nor have they deserved it for they have not represented any sufficient degree of originality. Later in the paper reference will be made to some fairly recent lenses which at first glance appear to differ considerably from the Petzval form but which on closer inspection are seen to be closely related to it.
* Scientific Bureau, Bausch and Lomb Optical Co. Rochester, N. Y.
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