Geometric Optics: Lenses
1 Introduction
In this experiment, we will continue to explore geometrical optics by studying the optics
of simple curved mirrors and lenses.
2 Background  see Pedrotti
3
, Sections 26 to 29
When studying the geometrical optics of mirrors or lenses one considers the following
three quantities: object distance
𝑠
𝑜
, image distance
𝑠
𝑖
, and focal length
𝑓
. These
quantities are related by the equation
1
𝑠
𝑜
+
1
𝑠
𝑖
=
1
𝑓
(1)
There is a convention to be followed in the definition of these quantities.
For lenses, a
converging lens (convex) has
𝑓
> 0 while a diverging lens (concave) has
𝑓
< 0. For
mirrors,
𝑓
> 0 for concave mirrors, and
𝑓
< 0 for convex mirrors. Also by convention, we
place the object to the left of the lens, with
𝑠
𝑜
> 0. If
𝑠
𝑖
> 0, it is on the right of the lens
and is a real image. If
𝑠
𝑖
< 0 it is to the left of the lens (same side as object) and is a
virtual image. One can consider the mirror as a folded over version of the lens:
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 Spring '11
 ENO
 Physics

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