How Does the Telescope Work?
First, remember these things …
• Beams of light normally travel in straight lines,
– But they bend when moving from one material to
another – e.g. from air into glass.
• Your eye and brain are fooled when light
bends: they think it has travelled in a straight
line.
Sticks seem to bend in water …
… But the eye thinks the light has
travelled in a straight line, so the end of
the stick appears to be here!
Stick
Air
Water
Light from the
end of the
stick bends as
it leaves the
water …
Simple Magnifier.
This is called a
convex lens
… Again, the eye
thinks light has
travelled in a straight
line, so sees a bigger
image
Light beams from a
small object close to
the lens bend like this
as they pass through
the lens…
Same lens, different effect
… The result is a real
image that can be seen
on a screen – by
everyone!
This time, light rays from
a distant object bend like
this – and meet at a
single point …
Another type of lens
It fools the eye into
seeing a smaller, virtual
image.
This is called a
concave lens. It bends
light the opposite way.
Your telescope uses both lenses …
As usual, your eye assumes light
has travelled in a straight line. This
means it sees a greatly magnified
image.
Light from a distant
object is bent inwards
by the front lens …
… then outwards by
the back lens.