The document discusses two main types of telescopes - refracting and reflecting. A refracting telescope uses two lenses, a large objective lens that collects light and forms a real image, and an eyepiece lens that magnifies this image for viewing. A reflecting telescope uses a concave mirror instead of an objective lens, collecting light via reflection rather than refraction. Reflecting telescopes are commonly used for large astronomical telescopes as mirrors can be made larger than lenses.

1. (Reflecting & Refracting)
by: Caryl Lou Cotejo

2. The Telescope (definition)
• It is an instrument which helps the human
eye see objects not ordinarily
visible
• It also increases the size
of an object’s image on
the retina.

3. Types of
Telescopes

4. Refracting Telescope
As we learned earlier , the direction of light
propagation is changed at the boundary of glass and
air by
. By designing lenses having the right
curvature, this principle can be used to gather and
focus light. The following figure illustrates the use of a
lens to gather and focus light, and the use of two
lenses to make a simple refracting telescope.

5. Refracting Telescope
Two types of lenses are used:
– a very large lens that
collects a large amount of light from a faraway
object. It also has a long focal length
This forms the object’s first
real, inverted and diminished image.

6. Refracting Telescope
– it has a short focal
length. It acts like a magnifying lens
for the image cast by the objective lens.
is closer to the eye. It
forms the final virtual,
enlarged image of the object.

7. Refracting Telescope

8. Reflecting Telescope
The following figure illustrates the principle
of reflection. The right side of the figure
illustrates the use of a mirror to make a
reflecting telescope.

9. Refracting Telescope
•
•
•
•
Many large astronomical
telescopes use concave mirrors
instead of objective lenses.

10. Telescopes of this type are called
REFLECTING TELESCOPES