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A Maximum-Minimum Method of Determining the Cardinal Points of a Lens System

Published online by Cambridge University Press:  24 October 2008

G. F. C. Searle
Affiliation:
Peterhouse

Extract

The method of determining the focal length f of a thin converging lens by finding the minimum distance Δ0 between image and object is well known. When the thickness of the lens is negligible, f = ¼Δ0.

In the general coaxial system, the media at the two ends have refractive indices μ1, μ2, and there is a finite distance t between the principal or unite plances. The two focal lengths are unequal, since, f1/f212, and the nodal points do not coincide with the principal points.

Type
Research Article
Copyright
Copyright © Cambridge Philosophical Society 1936

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References

* Searle, Experimental optics, Chapter ix.

The focal length f is positive or negative, according as the image of a distant object is inverted or erect. This is the definition used by practical opticians.