Using Your Telescope-Astronomical Observing; Cooling The Telescope; Focusing The Telescope - Orion Observer 60 EQ ultra Instruction Manual

lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. Set up on a
grass or dirt surface, not asphalt, because asphalt radiates
more heat. Heat disturbs the surrounding air and degrades
the images seen through the telescope. Avoid viewing over
rooftops and chimneys, as they often have warm air currents
rising from them. Similarly, avoid observing from indoors
through an open (or closed) window, because the tempera-
ture difference between the indoor and outdoor air will cause
image blurring and distortion.
If at all possible, escape the light-polluted city sky and head
for darker country skies. You'll be amazed at how many more
stars and deep-sky objects are visible in a dark sky!

cooling the telescope

All optical instruments need time to reach "thermal equilibri-
um." The bigger the instrument and the larger the temperature
change, the more time is needed. Allow at least a half-hour for
your telescope to cool to the temperature outdoors. In very
cold climates (below freezing), it is essential to store the tele-
scope as cold as possible. If it has to adjust to more than a
40° temperature change, allow at least one hour.
aiming the telescope
To view an object in the main telescope, first loosen both the
R.A. and Dec. lock knobs. Aim the telescope at the object you
wish to observe by "eyeballing" along the length of the tele-
scope tube (or use the setting circles to "dial in" the object's
coordinates). Then look through the (aligned) finder scope and
move the telescope tube until the object is centered on the
crosshairs. Retighten the R.A. and Dec. lock bolts. Then center
the object on the finder's crosshairs using the R.A. and Dec.
slow-motion controls. The object should now be visible in the
main telescope with a low-power (long focal length) eyepiece.

Focusing the telescope

Practice focusing the telescope in the daytime before using it for
the first time at night. Start by positioning the focuser drawtube
near the center of its adjustment range. Insert an eyepiece into
the star diagonal and secure with the thumbscrew. Point the
telescope at a distant subject and get it in the field of view. Now,
slowly rotate one of the focusing knobs 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 tele-
scope can only focus on objects at least 50 to 100 feet away. It
will not focus without the star diagonal in place.
As with all refractor telescopes used with a standard 90° star
diagonal, the image you see will be right-side up, but reversed
left-to-right. (Correct-image diagonals are available, and may
be purchased separately, though the image quality is slightly
reduced.)
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 portion 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:
Telescope focal length ÷ Eyepiece focal length = Magnification
For example, the Observer 60 EQ Ultra, which has a focal
length of 900mm, used in combination with a 25mm eyepiece,
yields a power of
900 ÷ 25 = 36x.
Every telescope has a useful limit of power of about 45x–60x
per inch of aperture (diameter of objective lens). Claims of
higher power by some telescope manufacturers are a mis-
leading advertising gimmick and should be dismissed. Keep
in mind that at higher powers, an image will always be dimmer
and less sharp (this is a fundamental law of optics). The
steadiness of the air (the "seeing") will limit how much magni-
fication an image can tolerate.
Always start viewing with your lowest-power (longest focal
length) eyepiece in the telescope. After you've located and
looked at the object with it, you can try switching to a higher-
power eyepiece to ferret out more detail, if atmospheric
conditions permit. If the image you see is not crisp and
steady, reduce the magnification by switching to a longer-
focal-length eyepiece. As a general rule, a small but
well-resolved image will show more detail and provide a more
enjoyable view than a dim and fuzzy, overmagnified image.
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, gal-
axies, and star clusters—or even very many stars, for that
matter. Your eyes take about 30 minutes to reach perhaps
80% of their full dark-adapted sensitivity. Many observers
notice improvements after several hours of total darkness. As
your eyes become dark-adapted, more stars will glimmer into
view and you'll be able to see fainter details in objects you
view in your telescope. Exposing your eyes to very bright
daylight for extended periods of time can adversely affect your
night vision for days. So give yourself at least a little while to
get used to the dark before you begin observing.
To see what you're doing in the darkness, use a red-filtered
flashlight rather than a white light. Red light does not spoil
your eyes' dark adaptation like white light does. A flashlight
with a red LED light is ideal, or you can cover the front of a
regular incandescent flashlight with red cellophane or paper.
Beware, too, that nearby porch and street lights and car head-
lights will ruin your night vision.
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