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-------------------------- Optics Primer - Focusing by Extension

--------------------------------------------------------- By Bill Claff

The patent specifies data for a magnification of 1/30th. This is actually listed as -1/30 because the image is inverted.
Let's feed rays in on the object side optical axis at the specified distances:

The entire lens has moved away from the image plane; this is called focusing by extension.

Let's zoom out to see the big picture:

Indeed, rays leaving the specified object plan arrive focused at the specified image plane.