Chapter 12

Lenses in Which Stop Position Is a Degree of Freedom

It is obvious that, depending on its position in a lens system, a stop selects some rays from an oblique pencil and rejects others. Thus, if the stop is moved along the axis (or for that matter, if it is displaced sideways, but that case will not be considered here), some of the former useful rays will be excluded while other previously rejected rays are now included in the image-forming beam. Consequently, unless the lens happens to be perfect, a longitudinal stop shift changes all the oblique aberrations in a lens. It will not affect the axial aberrations provided the aperture diameter is changed as necessary to maintain a constant f-number.

12.1 THE H′ − L PLOT

The results of a stop ...

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