Summary of mirrors and lenses

The mirror/lens equation:

The magnification equation(s):

SIGN CONVENTIONS:

For a mirror or lens, the light rays come into the optical device from one side; let’s call this the “IN” side. The light rays leave the mirror or lens on the “OUT” side. For a mirror, the “OUT” side is the same side as the “IN” side; for a lens, it’s the opposite.

Object on the “IN” side	dobj > 0
(not on the “IN” side)	dobj < 0
Image on the “OUT” side	dimg > 0
(not on the “OUT” side)	dimg < 0
Focus on the “OUT” side	f > 0 (concave mirrors, converging lens)
(not on the “OUT” side)	f < 0 (convex mirrors, diverging lens)

VOCABULARY WORDS:

d_obj, d_img > 0: REAL object, image

d_obj, d_img < 0: VIRTUAL object, image

M > 0: UPRIGHT

M < 0: INVERTED

| M | < 1: SMALLER

| M | = 1: SAME SIZE

| M | > 1: LARGER

You only get “virtual objects” if the object for one lens (or mirror) is the image from another lens (or mirror), which is arranged so that d_obj < 0 for the 2^nd imaging device. See section 26.9, which will be discussed Monday March 26.