Concave Spherical Mirrors
We start by considering the reflections from a concave spherical mirror in the paraxial approximation (ie small angles of incidence close to a single axis):
- First draw a ray (light blue) from the tip of the arrow through the center of the sphere. This ray is reflected straight back since the angle of incidence = 0.
- Note that the two rays intersect in a point, suggesting an inverted image.
- To check this, draw another ray (green) which is incident at angle a, as shown.
- Now draw a ray (white) from the tip of the arrow parallel to the axis. This ray is reflected with angle q as shown.
- Note that this ray intersects the other two at the same point, as it must if an image of the arrow is to be formed there.