The document summarizes the basic components and use of a telescope. It discusses that a telescope has two main components - an objective lens or mirror that gathers light, and an ocular lens or eyepiece that is used for viewing. It also mentions that telescopes are used to magnify distant objects and make them appear clearer. The document provides additional details on magnification depending on the eyepiece and telescope focal lengths. It describes the use of a finder, which is a smaller attached telescope, to first locate objects before viewing them in the main telescope for a smaller field of view. It gives tips on focusing the telescope and changing eyepieces to achieve different magnifications.

1. Telescope

2. Components of telescope
Objective lens or mirror
To gather and concentrate
light
Ocular lens or eyepiece
For viewing the focused
image

3. Basic Components of
Telescope

4. Basic Components of
Telescope

5. BRAIN TEASER. MABEL
 To magnify small images of
objects that are actually far and
large.
 Makes you see a clear image
of a very distant object.
Function of the
Telescope

6.  Choose the lowest
magnification
Starting to Use Your Telescope

7. Astronomical telescopes often come with
several eyepieces, of different focal lengths.
The magnification they give depends on
their focal length, and the focal length of
the telescope – that is in effect the length of
the tube. So an eyepiece will give a
different magnification depending on the
telescope, which is why they don’t usually
have the actual magnification marked on
them
Magnification

8. BRAIN TEASER. MABEL
Align the finder

9. This is either a small telescope or
a red-dot device attached to the
side of the tube, the idea being
that you locate the object using
the finder first, then it should be
in the main field of view of the
telescope.
Finder

10. Why is it needed to
use the finder first
rather than the main
telescope?

11. ANSWER:
The field of view of the main
telescope is very magnified, so you
only see a tiny bit of sky at any one
time. The finder shows you a wider
view of the sky and acts as a peep
sight to help you line up the
telescope.

12. First Step in Observing
Try adjusting the focus in and out and as you
do even if it’s blurred the image should get
brighter and smaller as you approach the
focus point. If it’s way out of focus and
you’re not sure what’s happening, move the
telescope slightly so that you can see one
edge of the blurred disc rather than a
general patch of light, and you should see it
getting more focused.

13. In principle all you need to do
is to change the eyepiece for
one of shorter focal length,
and away you go.
Using Different Eyepiece

14. Part of the Moon at medium power (left) and high power (right). Notice how
the field of view gets smaller and the image gets diummer as you increase the
magnification. The area shown is the Mare Tranquillitatis, where the Apollo 11
landing took place

15. The left view shows the Crab Nebula as you might see it at low power. But
with a higher power the object may disappear if it is not dead centre and
the new eyepiece is slightly out of focus (right)

16. Activity