Archetypes for lenses
To summarize, there are just three distinct possibilities for images of a real object produced by a
lens:
- Converging lens (f positive) with object farther away than the focal point
(d0 > f):
Image is real and inverted (examples: camera lens).
- Converging lens (f positive) with object closer than the focal point
(d0 < f: image is virtual, upright, enlarged (example: magnifying glass).
- Diverging lens (f negative): image is virtual, upright, "smallified"
(examples: peephole lens used in apartment doors).
These three possibilities can easily be derived by making sketches or by using the equations
1/di + 1/do = 1/f
and
M = -di / do. The same equations hold for curved mirrors, so the
same three possibilities exist also for mirrors as we have already seen.
lenses index
examples
Lecture index