Telescope

Components of telescope

Objective lens or mirrorTo gather and concentrate

lightOcular lens or eyepiece

For viewing the focused image

Basic Components of Telescope

Basic Components of Telescope

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

Choose the lowest magnification

Starting to Use Your Telescope

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

Magnif ication

BRAIN TEASER. MABEL

Align the finder

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

Why is it needed to use the finder first

rather than the main telescope?

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.

First Step in ObservingTry 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.

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

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

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)

Activity