Photographic Sharpness and Resolving PowerI The Design and Performance of an Apochromatic Resolving-Power Camera Objective*

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Abstract
The excessive residual aberrations of the ordinary achromatic doublet that had been regularly used to photograph resolving-power test objects on film samples in these Laboratories led to the construction of a special air-spaced apochromatic triplet containing fluorite. So excellent is the correction of the new lens that the Airy disk is white and changing the focus setting to fit the spectral sensitivity of the sample is unnecessary, except when the sensitivity peak is at a wave-length longer than 580 mµ. The improvement in measured resolving power over the values obtained with the former lens is slight for materials of high resolution but is marked for materials whose values are below about 100 lines per millimeter. Curves are presented showing the effect on resolving power of stopping down the new objective, and it is shown that this lens, whose aperture is ƒ/5, is not adequate for materials exceeding 150 lines per millimeter or so, failing simply because of its comparatively low aperture. These results emphasize the dependence of resolving-power values on the aperture and the corrections of the camera lens. The loss in the resolving power of this lens caused by mal-focusing is also compared with that of an anastigmatic photographic objective.

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