Abstract
INTERFEROMETERS for the testing and corretion of prisms and of lenses (for axial pencils) have been described in the Philosophical Magazine (vol. xxxv., January, 1918, p. 49). In its simplest form the instrument resembles the well-known Michel-son interferometer, the essential optical dift'erence being that the two interfering beams of light are brought to a focus at the eye of the observer. The principles of the prism interferometer have been applied to photographic lens testing in the camera lens interferometer recently constructed by Messrs. Adam Hilger, Ltd. A plan of the instrument is shown in Fig. 1, and a side elevation in Fig. 2. Light from a suitable source is reflected by a mirror 10 into the interferometer. A convex spherical mirror ooi is so disposed that its centre of curvature coincides with the focus of the lens 14 which is under test. In these circumstances, a beam the wave-front of which is a plane perpendicular to the axis of the lens will, after passage through the lens, be reflected back on its own path by the convex mirror, and if the lens be free"from spherical aberration the reflected beam will, after passage through the lens, once more have a plane wave-front. If it has not, then the departure from planeness will produce interference bands which form a contour map of the corrections which will have to be applied to the lens to make its performance perfect.
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An Interferometer for Testing Camera Lenses1. Nature 107, 635–636 (1921). https://doi.org/10.1038/107635a0
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DOI: https://doi.org/10.1038/107635a0