Caption: The blue object is point inverted through the black dot to form the red image---or vice versa mutatis mutandis.

Features:

1. If a point is located at vector R from an origin, then a point inversion locates the image point vector -R from the origin.

2. A point inversion can also be regarded as a 180° rotation about a point of every part of an object.

3. Point inversion is physically realized in image formation in most reflector telescopes and in the Keplerian telescope (a refractor telescope).

4. It can be corrected for, but most astronomers don't care---real astronomers like looking at point inverted images---so what if it's tricky to map what you see to what is in the sky.

5. The origin for the point inversion is the point the optical axis of the telescope (which is the symmetry axis of the telescope) becomes when looked end-on.

6. The actual observed origin for the point inversion is the center of the field of view (FOV) of the telescope.