National Geographic : 1922 Apr
0j) Testing the Infinitesimal From the slabs of optical glass to the finished product, each Kodak Anastigmat lens must successfully emerge through ten rigid tests, performed in ten dfferent depart ments. Even in two final tests which are identical, the judg ment of one set of inspectors is pitted against that of another. The exacting nature of this work is indicated in the test for curvature. Here, so delicate is the adjustment that the warmth of the inspector's hand, if the fingers and glass are in contact longer than a few seconds, alters the lens shape sufficiently to prevent a fair verdict. Of course such a change, while instantly detected, is in finitesimal, but as this particular test rejects deviation from the theoretically perfect curve of more than 1/30,000 of an inch, "the infinitesimal" is the very thing the inspector is concerned about. Send for free booklet "About Lenses." It contains interesting information that you ought to have. Thi . K Eastman Kodak Company AN, T G ATS Rochester, N. Y. .77 4d4.5 "Mention The Geographic-It identifies you"