Optical Instruments

Mirrors are wonderful, and so are lens; great for all sorts of practical applications. I want to talk about two types of mirrors and two types of lenses. Mirrors can be concave or convex, and lens can be concave or convex.

(assuming the left focal point is the closest & the right focal point is the furthermost focal point)
Let's start with a concave mirror:

1) The ray parallel to the axis reflects through focal point.
2) The ray through the focal point reflects parallel to the axis.
3) The ray through the center of curvature intersects the surface normally and reflects along its original path.
4) The ray to the vertex reflects symmetrically about the optical axis. (e.i.- the angle of incident = the angle of reflection)

Ok, now the convex mirror:

1) A ray shot parallel to the optical axis appears to come from the furthermost focal point.
2) A ray shot towards the furthermost focal point reflects parallel to the optical axis.
3) A ray shot towards the center of curvature intersects the surface normally and reflects along its original path.
4) A ray shot towards the vertex of the mirror reflects symmetrically about the optical axis.

Ok, now the concave lens:

1) The ray moving parallel to the optical axis appears to have come from the closest focal point.
2) The ray moving trough the vertex does not deviate.
3) The ray moving towards the furthermost focal point emerges parallel to the optical axis.

Ok, now the convex lens:

1) The ray moving parallel to the optical axis emerges traveling through the furthermost focal point.
2) The ray moving through the center of the lens does not deviate.
3) The ray moving through the closest focal point emerges parallel to the optical axis.