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--------------------------------- Optics Primer - Magnification

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

We can verify the stated magnification with rays that run between the edges of the object and image planes:

Note that the specified height of the image plane is the diameter of the image circle.

Let's look more closely at the focal point:

The distance between the focal point (F') and the image plane (I) relates to magnification as follows:
m = x / f
where m is magnification, x is extension from the image plane, and f is focal length.

This is how extension tubes increase magnification.

Note that x is zero at infinity and magnification is zero at infinity.

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