Convex and Concave Even the image on the flag is of reversible cubes. One can view these features as concave by viewing the image upside-down. All additional elements and decoration on the left are consistent with a viewpoint from above, while those on the right with a viewpoint from below: hiding half the image makes it very easy to switch between convex and concave. Convex and Concave Convex and Concave is a lithograph print by the Dutch artist M. C. Escher, first printed in March 1955. It depicts an ornate architectural structure with many stairs, pillars and other shapes. The relative aspects of
Telecentric lens Telecentric lens A telecentric lens is a compound lens that has its entrance or exit pupil at infinity; in the prior case, this produces an orthographic view of the subject. This means that the chief rays (oblique rays that pass through the center of the aperture stop) are parallel to the optical axis in front of or behind the system, respectively. The simplest way to make a lens telecentric is to put the aperture stop at one of the lens's focal points. An entrance pupil at infinity makes the lens object-space telecentric. Such lenses are used in machine vision systems