透镜成像

Three rays that locate any image

The center ray is a pinhole

Image size follows the distances

Framing and the field of view

A world point sits off the optical axis above the lens. Which ray construction gives its image position in the plane one has already found with the lensmaker relation?

Two portraits of the same face are taken with the head filling the frame. The first uses a short lens from close range, the second a long lens from far away. Why does the close shot enlarge the nose relative to the ears?

An object of height $4$ centimeters stands $a = 100$ centimeters in front of a lens whose conjugate image distance is $b = 20$ centimeters. Using image height equal to object height times $b/a$, compute the image height in centimeters and write the number.