Focal Plane (of a light)

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2-2-170

The horizontal plane through the focus of the optical apparatus of the light.

Ch2 Fig10.jpg


Note: In lighthouse practice in some countries the term "focal plane" is used with the above meaning, although this is quite a different meaning from that of 2-2-165.




Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)