In planning the equipment for the recently established Institute of Applied Optics at the University of Rochester, it was decided to build a photographic lens testing bench, which should be suitable both for instruction to students and for research work. A description of the construction, adjustment, and use of the bench is given in the present paper.
In designing the bench, it was decided to use a distant point source of light or other suitable test object, and to mount the lens so that it can be rotated about a vertical axis through its second nodal point, and set at any desired obliquity up to 60°. The image formed by the lens is then examined with a microscope in the usual way. It was also decided to incorporate an automatic mechanism to ensure that the focusing point of the microscope is always in the ideal flat field which the lens should have; and further, to provide such auxiliary motions as are necessary to test telephoto lenses.
Scales are provided for the direct measurement of astigmatism, curvature of field, distortion, and oblique color; and by suitable means it is also possible to determine the amount of spherical and chromatic aberration should this be required. The range of focal lengths is from 5 to 60 cms with a provision for the direct measurement of the equivalent focal length and the back focus of the lens.
The bench contains within itself adequate means for making complete adjustments of all its parts, and for correctly setting the zeros of all scales.
The paper is divided into four sections:
- I Theoretical considerations
- II Mechanical construction of the bench
- III Adjustments of the various parts
- IV Criticisms of the design.
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