Curved mirror the focal point of the optical device. Boxes 1 and 3 feature summing the angles of a triangle and comparing to π radians (or 180°). Box 2 shows the Maclaurin series of formula_16 up to order 1. The derivations of the ray matrices of a convex spherical mirror and a thin lens are very similar. Curved mirror A curved mirror is a mirror with a curved reflecting surface. The surface may be either "convex" (bulging outwards) or "concave" (bulging inwards). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in
Parallel projection Parallel projection A parallel projection is a projection of an object in three-dimensional space onto a fixed plane, known as the "projection plane" or "image plane", where the "rays", known as "lines of sight" or "projection lines", are parallel to each other. It is a basic tool in descriptive geometry. The projection is called "orthographic" if the rays are perpendicular (orthogonal) to the image plane, and "oblique" or "skew" if they are not. A parallel projection is a particular case of "projection" in mathematics and "graphical projection" in technical drawing. Parallel projections can be seen as the limit of a