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Re: [Phys-l] Image of object placed at focal point



Rick Tarara wrote:
when p = f an image of each type would form at +/- infinity, but practically speaking that means that no usable image forms.

Astronomers might have a different opinion about the practicality of
focussing on infinity.

My answer to the original question is:

5) There are two images:
5a) One real image at +infinity, inverted and verrry greatly magnified.
5b) One virtual image at -infinity, upright and verrry greatly magnified.

For suitable definitions of (+) and (-).
As usual, infinity is defined in terms of a limit.

The virtual image is considerably less useful than the real image, and
is commonly neglected.