telescopes with electric focuser

1. TELESCOPES
How do they work?

2. Prepared by,
Sarker,A.S.M. Imrul Hasan
Momen, Mahfuja
Ahammod Moeen Uddin
Hossain,Md. Alamin
Presented to,
Rethwan Faiz

3. WHY CAN’T WE SEE AN
OBJECT THAT IS FAR AWAY?
The answer is simple: the object does not take up much space
on our eye’s screen (retina).
Using a digital camera analogy, at 150 feet the writing on a
dime does not cover enough pixels on our retinal sensor to
read the writing.
This can be corrected by bending the light with lenses.

4. HOW DOES THIS APPLY TO
TELESCOPES?
 If we had a bigger eye, we could collect more
light from the object. This image could be
magnified so it stretches out over more pixels in
your retina.
 In a telescope, two pieces make this possible:
 the objective lens (refractor telescopes) or primary
mirror (reflecting telescopes)
 the eye piece

5. • The objective lens (in refractors) or primary mirror
(in reflectors) collects lots of light from a distant object
and brings that light to a point or focus.
• An eyepiece lens takes the bright light from the focus of
the objective lens or primary mirror and "spreads it out"
(magnifies it) to take up a large portion of the retina.
This is the same principle that a magnifying glass (lens)
uses; it takes a small image on the paper and spreads it
out over the retina of your eye so that it looks big.

6. Diagram of a simple telescope. Parallel light rays enter from the left,
pass through the objective lens, come to a focus at the focal plane, and
exit through the eyepiece lens. The focal length of the objective is F, and
the focal length of the eyepiece is f.

7. A TELESCOPE HAS TWO
GENERAL PROPERTIES
 how well it can collect the light
(the aperature)
 how much it can magnify the image
(the magnification)

8. THE APERTURE
 A telescope's ability to collect light is directly related to the
diameter of the lens or mirror -- the aperture -- that is used to
gather light. Generally, the larger the aperture, the more light
the telescope collects and brings to focus, and the brighter
the final image.

9. MAGNIFICATION
 The telescope's magnification, its ability to enlarge an image,
depends on the combination of lenses used. The eyepiece
performs the magnification. Since any magnification can be
achieved by almost any telescope by using different
eyepieces, aperture is a more important feature than
magnification

10. EYEPIECE
The purposes of the eyepiece are to:
 produce and allow you to change the telescope's
magnification
 produce a sharp image
 provide comfortable eye relief (the distance
between your eye and the eyepiece when the
image is in focus)
 determine the telescope's field of view:
 apparent - how much of the sky, in degrees, is seen
edge-to-edge through the eyepiece alone (specified on
the eyepiece)
 true or real - how much of the sky can be seen when that
eyepiece is placed in the telescope (true field =
apparent field/magnification)

11. THERE ARE 2 MAIN TYPES OF
TELESCOPES
 Refractor telescopes, which use glass lenses
 Reflector telescopes, which use mirrors instead of lenses.
Both types accomplish exactly the same thing,
but in completely different ways. Refractor
telescope is the simplest one.

12. REFLECTING TELESCOPES FOCUS LIGHT BY BENDING
THEM WITH MIRRORS

13. ELECTRIC FOCUSER
 Electric focusers can move a focuser in 1/1000th of an inch
increments to achieve a focusing accuracy impossible to
achieve manually. They can also slew from close focus to
infinity in a matter of seconds. Electric focusers provide totally
hands-off focusing, so frustrating telescope vibration from
groping for the focuser knob in the dark is virtually eliminated.
You get faster photographic focusing and more time to
observe visually. Electric focusers simply make observing more
fun.

14. CIRCUIT DIAGRAM OF FOCUSER

15. FAMOUS TELESCOPES
 Keck Telescope
 Kitt Peak Observatory

16. VERY LARGE ARRAY (VLA)
RADIO TELESCOPES

17. THANK YOU