Celestron Firstscope 80 AZ Instruction Manual page 8

The Eyepieces
The eyepiece, or ocular, is an optical element that magnifies the image focused by the
telescope. The eyepiece(s) fit into either the accessory adapter directly or into the
diagonal. To install an ocular:
1. Loosen the set screw on the diagonal so that it does not obstruct the inner
diameter.
2. Slide the chrome portion of the eyepiece into the diagonal.
3. Tighten the set screw.
To remove the ocular:
1. Loosen the set screw on the diagonal.
2. Slide the eyepiece out of the diagonal.
You can replace it with another ocular.
Eyepieces are commonly referred to by focal length, which is printed on the eyepiece
barrel. The longer the focal length (i.e., the larger the number) the lower the power.
Conversely, the shorter the focal length (i.e., the smaller the number) the higher the
magnification. Generally, you will use low to moderate power when viewing. For
more information on how to determine power, see the section on "Calculating
Magnification."
Focusing
To focus your telescope, simply turn either of the focus knobs located directly
opposite the finderscope. Turn the focus knob until the image is sharp. Once
sharp, turn the knob towards you to focus on an object that is closer than the
one you are currently observing. Turn the knob away from you to focus on a
more distant object than the one you are currently observing.
In addition to understanding how the focusing mechanism works, there are a
few focusing hints to remember when using any optical instrument.
• Avoid looking through glass. Glass found in household windows is optically
imperfect, and as a result, may vary in thickness from one part of a window
to the next. This inconsistency can and will affect the ability to focus your
telescope. In most cases, you will not be able to achieve a truly sharp
focus. In some cases, you may actually see a double image.
• Never look across or over objects producing heat waves. This includes
asphalt parking lots on hot summer days or building rooftops.
• Hazy skies, fog, and mist can also make it difficult to focus when viewing
terrestrially. The amount of detail that can be seen under these conditions
will be greatly reduced. Also, when photographing under these conditions,
the processed film may come, out a little grainier than normal.
• When using your telescope as a telephoto lens, the split screen or microprism
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