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:
dobj, dimg > 0: REAL object, image
dobj, dimg < 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 dobj < 0 for the 2nd imaging device. See section 26.9, which will be discussed Monday March 26.