When an object is placed at infinity, the rays coming from it are parallel to each other. Let us consider two rays, one striking the mirror at its pole and the other passing through the centre of curvature. The ray which is incident at the pole gets reflected according to the law of reflection and the second ray which passes through the centre of curvature of the mirror retraces its path.
These rays after reflection form an image at the focus. The image formed is real, inverted and diminished.
The image is at F
Real
Inverted
Diminished
