sary, use the R.A. and Dec.
Focusing the Telescope
Practice focusing the telescope in the daytime before using it for the first time at night. Start by turning the focus knob until the focuser drawtube is near the center of its adjustment range. Insert the star diagonal into the drawtube and an eyepiece into the star diagonal (secure with the thumbscrews). Point the tel- escope at a distant subject and center it in the field of view. Now, slowly rotate the focus knob until the object comes into sharp focus. Go a little bit beyond sharp focus until the image just starts to blur again, then reverse the rotation of the knob, just to make sure you hit the exact focus point. The telescope can only focus on objects at least 50 to 100 feet away.
Do You Wear Eyeglasses?
If you wear eyeglasses, you may be able to keep them on while you observe, if your eyepieces have enough “eye relief” to allow you to see the whole field of view. You can try this by looking through the eyepiece first with your glasses on and then with them off, and see if the glasses restrict the view to only a por- tion of the full field. If they do, you can easily observe with your glasses off by just refocusing the telescope the needed amount.
Calculating the Magnification
It is desirable to have a range of eyepieces of different focal lengths, to allow viewing over a range of magnifications. To calculate the magnification, or power, of a telescope, simply divide the focal length of the telescope by the focal length of the eyepiece (the number printed on the eyepiece):
Magnification = Telescope Focal Length (mm)
Eyepiece Focal Length (mm)
For example, the AstroView 120mm, which has a focal length of 1000mm, used in combination with a 25mm eyepiece, yields a power of
1000 ÷ 25 = 40x.
Every telescope has a useful limit of power of about
Always start viewing with your
Use of 2" Eyepieces
Another nice feature of the AstroView 120 is its ability to use either 1.25" or 2"
able for observing
To use 2" eyepieces, simply loosen the two large setscrews on the focuser drawtube that are just in front of the setscrew that holds the provided 1.25" star diagonal in place. Once these setscrews are loosened, the entire back end of the focuser, including any 1.25 diagonal and eyepiece that may be attached, comes off, exposing the 2" diameter focuser drawtube. Now, insert your 2" star diagonal into the drawtube and secure with the two setscrews loosened pre- viously. Insert a 2" eyepiece into the 2" diagonal, secure it in place with the setscrew on the diagonal, and you’re ready to observe.
Let Your Eyes Dark-Adapt
Don’t expect to go from a lighted house into the darkness of the outdoors at night and immediately see faint nebulas, galaxies, and star
To see what you’re doing in the darkness, use a
“Seeing” and Transparency
Atmospheric conditions vary significantly from night to night. “Seeing” refers to the steadiness of the Earth’s atmosphere at a given time. In conditions of poor seeing, atmospheric turbu- lence causes objects viewed through the telescope to “boil.” If the stars are twinkling noticeably when you look up at the sky with just your eyes, the seeing is bad and you will be limited to viewing with low powers (bad seeing affects images at high powers more severely). Planetary observing may also be poor.
In conditions of good seeing, star twinkling is minimal and images appear steady in the eyepiece. Seeing is best over- head, worst at the horizon. Also, seeing generally gets better after midnight, when much of the heat absorbed by the Earth during the day has radiated off into space.
Avoid looking over buildings, pavement, or any other source of heat, as they will cause “heat wave” disturbances that will distort the image you see through the telescope.
Especially important for observing faint objects is good “trans-
Note About Chromatic Abberation
Chromatic abberation literally means color distortion. Whenever light passes through one material to another, light of different wavelengths (color), is bent by different amounts. This is a prob-
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