Telescopes

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When you combine the objective lens or primary mirror with the eyepiece, you have a telescope.

Again, the basic idea is to collect lots of light to form a bright image inside the telescope, and then use something like a magnifying glass to magnify (enlarge) that bright image so that it takes up a lot of space on your retina.

Slide 10

A telescope has two general properties

how well it can collect the light

(the aperature)

how much it can magnify the image

(the magnification)

Slide 11

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.

Slide 12

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

Slide 13

A closer look at eyepieces

Slide 14

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)

Slide 15

Filters

Filters are pieces of glass or plastic that you can place in the barrel of an eyepiece to restrict the wavelengths of light that come through in the image.

Set of filters for viewing, including a light pollution filter (left) and colored filters for enhancing contrast in planetary images.

Filters can be used to:

enhance the viewing of faint sky objects in light-polluted skies

enhance the contrast of fine features and details on the moon and planets

safely view the sun

Slide 16

There are 2 main types of Telescopes