They work on different principles, but Lenses do the same job as Mirrors.

1
They work on different principles, but Lenses do
the same job as Mirrors. Lenses produce images
by redirecting the light rays that pass through
them. The biggest difference between lenses
and mirrors is that light reflects off a mirror,
but goes through a mirror.
2
Light passing through a lense makes one
significant difference in the behavior of lenses
compared to mirrors. Since light can go either
way through a lens, the lens has TWO focal
points, one either side of the lens, spaced the
same distance away from the lens. Both of them
are important to understanding how a lens
behaves. How those focal points behaves depends
on the type of lens there are two types, named
converging and diverging for what light rays do
when they go through the lens. The simple way to
tell the difference between converging and
diverging lenses is to look at the center and the
edges converging lenses are thicker in the
center than the edges, while diverging lenses are
thicker at the edges than in the center.
3
If you looked at a cross section of an example of
each type of lens, here is what you would see
Converging Lens Center Thicker than Edges
Diverging Lens Edges Thicker than Center
Do 3 in Class Exercises
4
Because light goes through a lens, the object and
the observer are on different sides of the lens
we will call them the obj. side and the obs.
side, respectively and the two focal points get
labeled for which side they are on.
Observer
Object
Axis
Obj. Focal Point
Obs. Focal Point
As with mirrors, an image that is on the
observers side is called a real image and an
image on the far side from the observer is called
a virtual image
5
Drawing a Converging Lens Ray Diagram
Special Ray 1 Incoming light ray parallel to
axis Outgoing on trajectory through obs. focal
point
.
.
F
F
6
Drawing a Converging Lens Ray Diagram
Special Ray 2 Incoming light ray through obj.
focal point Outgoing parallel to axis
.
.
F
F
7
Drawing a Converging Lens Ray Diagram
Special Ray 3 Incoming light ray through
center of lens Outgoing through center of lens
.
.
F
F
8
Drawing a Converging Lens Ray Diagram
Step 1 Incoming light ray parallel to axis
Outgoing on trajectory through obs. focal point
.
.
F
F
Object distance more than twice focal length
9
Drawing a Converging Lens Ray Diagram
Step 2 Incoming light ray through obj. focal
point Outgoing parallel to axis
.
.
F
F
Object distance more than twice focal length
10
Drawing a Converging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
Object distance more than twice focal length
11
Drawing a Converging Lens Ray Diagram
Step 4 Draw image where refracted lines meet
or appear to meet.

• IMAGE IS
• Inverted
• Real
• Smaller than object
• Closer than object

.
.
F
F
Object distance more than twice focal length
12
Drawing a Converging Lens Ray Diagram
Step 1 Incoming light ray parallel to axis
Outgoing on trajectory through obs. focal point
.
.
F
F
Object distance between F and 2F
13
Drawing a Converging Lens Ray Diagram
Step 2 Incoming light ray through obj. focal
point Outgoing parallel to axis
.
.
F
F
Object distance between F and 2F
14
Drawing a Converging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
Object distance between F and 2F
15
Drawing a Converging Lens Ray Diagram
Step 4 Draw image where refracted lines meet
or appear to meet.

• IMAGE IS
• Inverted
• Real
• Larger than object
• Further than object

.
.
F
F
Object distance between F and 2F
16
Drawing a Converging Lens Ray Diagram
Step 1 Incoming light ray parallel to axis
Outgoing on trajectory through obs. focal point
.
.
F
F
Object within focal point
17
Drawing a Converging Lens Ray Diagram
Step 2 Incoming light ray through obj. focal
point Outgoing parallel to axis
.
.
F
F
Object within focal point
18
Drawing a Converging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
Object within focal point
19
Drawing a Converging Lens Ray Diagram
Step 4 Draw image where refracted lines meet
or appear to meet.

• IMAGE IS
• Upright
• Virtual
• Larger than object
• Further than object

.
.
F
F
Object within focal point
20
Drawing a Diverging Lens Ray Diagram
Special Ray 1 Incoming light ray parallel to
axis Outgoing on trajectory through obj.
focal point
.
.
F
F
21
Drawing a Diverging Lens Ray Diagram
Special Ray 2 Incoming light ray through
obs. focal point Outgoing parallel to axis
.
.
F
F
All objects
22
Drawing a Diverging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
23
Drawing a Diverging Lens Ray Diagram
Step 1 Incoming light ray parallel to axis
Outgoing on trajectory through obj. focal point
.
.
F
F
All objects
24
Drawing a Diverging Lens Ray Diagram
Step 2 Incoming light ray through obs. focal
point Outgoing parallel to axis
.
.
F
F
All objects
25
Drawing a Diverging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
All objects
26
Drawing a Diverging Lens Ray Diagram
Step 4 Draw image where refracted lines meet
or appear to meet.

• IMAGE IS
• Upright
• Virtual
• Smaller than object
• Closer than object

.
.
F
F
All objects
27
Drawing a Diverging Lens Ray Diagram
Step 1 Incoming light ray parallel to axis
Outgoing on trajectory through obj. focal point
.
.
F
F
All objects
28
Drawing a Diverging Lens Ray Diagram
Step 2 Incoming light ray through obs. focal
point Outgoing parallel to axis
.
.
F
F
All objects
29
Drawing a Diverging Lens Ray Diagram
Step 3 Incoming light ray through center of
lens Outgoing through center of lens
.
.
F
F
All objects
30
Drawing a Diverging Lens Ray Diagram
Step 4 Draw image where refracted lines meet
or appear to meet.

• IMAGE IS
• Upright
• Virtual
• Smaller than object
• Closer than object

.
.
F
F
All objects