The document provides an overview of different types of telescopes, including refracting, reflecting, and catadioptric telescopes, and their components such as lenses and mirrors. It explains how each type gathers and focuses light to produce images of distant objects, along with their advantages and disadvantages. Additionally, it touches on radio telescopes and poses questions regarding the functioning of optical instruments.

1. (Reflecting &
Refracting)

2. Hey, it’s me!
HANS
LIPPERSHEY!
Galileo Galilei at your
service! I made my own
version of telescope but it’s
NOT ME who invented it.

3. 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.

4. Two Basic Parts of Optical Telescopes:
1. – a very large
lens that collects a large amount of light from
a far away object.
This forms the object’s first
real, inverted and diminished image.

5. 2. – it has a
short focal length. It acts like a magnifying
lens for the image cast by the objective lens.
It forms the final virtual,
enlarged image of the object.

6. • A lens is a curved piece of glass or other
transparent material that is used to refract light.
• A convex lens is
thicker in the center
than at the edges.
• A concave lens is
thinner in the center
than at the edges.

7. Types of
Telescopes

8. • The simplest type of telescope. It consist of a two-
lens eyepiece at one end of a long tube and a large
convex objective lens at the other end.
• Light enters through a main
objective lens at one end (1).
• The lens refracts (or bends) the
light to a point called focus (2).
• This is then magnified to form an
image by the eyepiece at the
other end (3).

9. Refracting Telescope
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.

11. Disadvantages:
• They can be heavy because of
their need for large lenses.
• They can also have a large
body which may impact on
transportation and storage.
• They may also be expensive,
as large high quality lenses are
more costly to produce.
Advantages:
• Generally easy to use
• More reliable as their
optics are permanently
fixed and aligned.

12. •
• Many large astronomical
• telescopes use concave mirrors
• instead of objective lenses.

13. Telescopes of this type are called
REFLECTING TELESCOPES

14. A reflecting telescope is similar to a refracting
telescope, but just a little bit more complex. It is called
a reflecting telescope because it uses mirror to reflect
the light internally, into the eyepiece.
• Light enters at (1).
• It is then reflected by a concave
shaped primary mirror at the
other end (2) towards a smaller
mirror known as the secondary
mirror.
• This mirror reflects (3) the light
into the eyepiece, which is
usually mounted on the side of
the telescope (4).

15. 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.

16. Advantages:
• Fairly compact and portable
• Generally more affordable
too.
• The mirrors inside can
typically produce less
optical aberrations than
lenses of the same value.
Disadvantages:
Mirrors need regular re-aligning as they
can easily slip out of alignment due to
knocks and bumps or even temperature
changes. In some cases, they can also be
susceptible to spherical aberrations.

17. • The Catadioptric could be considered a hybrid
refracting/reflecting telescope, in that it uses both
mirrors and lenses to form the image you see.
• Light enters at one end through a correcting
lens, which help reduce aberrations (1).
• It is then reflected by the primary mirror (2)
at the other end back towards the secondary
mirror mounted in the center of the
corrective lens.
• Here it is reflected (3) back towards a hole in
the primary mirror and into the eyepiece (4)
• When focusing, it is the primary mirror that is
moved, not the eyepiece.

18. Disadvantages:
They may suffer a slight loss of light
because of the positioning of the
secondary mirror.
Also catadioptrics may suffer from
image shift, or a jump in focus, due to
the primary mirror being moved when
focusing.
Advantages:
• Extremely compact and
portable.
• The optics provide the
advantages of both
lenses and mirrors, so
they make a great all
purpose telescope.

19. It can also be from atomic and
subatomic particles which we
called RADIATIONS.

20. What kind of telescope is invented to
detect this radiations?

21. Instrument that
is used to detect
radio waves and
obtain numerous
information
about the space
beyond.

22. • A radio telescope consist of a parabolic (disk-
shaped) mirror that reflects radio waves to a
preamplifier. The preamplifier converts the
waves into electronic impulses, which are then
fed into an electronic mixer that reconverts
the electronic signals and visual images.

23. Generalizations:
• How do scientist gather information from the
space beyond the solar system?
• How do refracting and reflecting telescopes
form images of distant objects?
• What does a radio telescope do?

24. Tell whether the following statements are TRUE or FALSE.
1. An optical telescope is used to magnify the image of a
distant object to make it look closer.
2. A refracting telescope is an optical telescope that
uses a mirror to collect light.
3. An optical telescope collects light waves while a radio
telescope collects radio waves.
4. Convex lenses are used in a reflecting telescope.
5. A concave lens can produce only virtual images
because parallel light rays passing through the lens
never meet.

25. B. Arrange the jumbled letters in order to find the
answer in the following questions/ statements.
SHPLREIPEY 1. A Dutch optician who invented a “spy glass” which is then
renowned as telescope.
EBJOVICET SELN 2. A very large lens that collects a large amount of light from a
far away object.
COFSU 3. It is the point where the lens in a refracting telescope refracts
(or bends) the light.
IDORA SLECOTEPE 4. Instrument that is used to detect radio waves and obtain
numerous information about the space beyond.
EEECYPEI 5. It forms the final virtual, enlarged image of the object.

26. • Explain how a refracting telescope forms a
magnified image of a distant object.
• Describe a reflecting telescope.
• What are stars?
• Why do stars twinkle?