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
Lens (optics) real object at the location of that virtual image. Likewise, it appears to a subsequent lens as if it were an object at that location, so that second lens could again focus that light into a real image, "S" then being measured from the virtual image location behind the first lens to the second lens. This is exactly what the eye does when looking through a magnifying glass. The magnifying glass creates a (magnified) virtual image behind the magnifying glass, but those rays are then re-imaged by the lens of the eye to create a "real image" on the retina.