Background Information:

Lenses are pieces of clear 
material that bend light in a 
particular way. A  lens that 
has sides that curve out is 
called a convex lens. A lens
that has sides that curve in 
is called a concave lens. 

When light rays bounce off something, such as a ball or a top, the light rays form a 
picture of that object. This 
picture is called an image. A
lens changes the image that
you see by bending light 
before it gets into your eyes.

Lenses can bend light so 
that all the light bouncing off
an object comes together at
one place. The spot where
all the light comes together
is called the focal point of 
the lens. The distance 
between the lens and its 
focal point is called the focal
length of the lens.

Sometimes the image of an 
object is very clear and 
sharp, and sometimes the 
image is blurry. A sharp, 
clear image is in focus, while a blurry image is out of focus.

A convex lens brings light 
rays together. If the object is placed within the focal 
length of the lens, the image
you see will be right-side 
up. If the object is placed 
outside the focal length of 
the lens, the image will be 
upside down. Convex 
lenses can also make the 
object look bigger or smaller
than it actually is.

Concave lenses make rays 
of light spread apart. The 
image of an object seen 
through a concave lens is 
always upright and smaller 
than the object.