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The ED66-CF features a two-element 66mm-diameter objec-
tive lens, with one element made from FLP-51 “extra-low
dispersion” (ED) optical glass. Inclusion of this glass ele-
ment greatly minimizes chromatic aberration, or color fring-
ing, which is an inherent aberration in achromatic refractors.
The objective lens is “fully multi-coated,” which means that all
air-to-glass optical surfaces are multi-layer coated with anti-
reflection material, to provide the highest possible light trans-
mission to the eyepiece.
About the Dual-Speed Crayford
Focuser
The ED66-CF comes equipped with a 1.25" dual-speed Crayford
focuser (
Figure 2A). The Crayford design allows for smooth,
precise focusing without the image shift that rack-and-pinion
designs experience. Ten turns of the fine focus wheel on the
right side equals one turn of the coarse (rubber-grip) adjust-
ment wheel. Once you have achieved the best possible focus
on an object using the coarse adjustment wheel, you can fine-
tune your focus using the fine focus wheel to make micro adjust-
ments, to zero in on the precise focus point.
You can make adjustments to the focuser drawtube tension by
using the drawtube tension thumbscrew located on the bottom of
the focuser (
Figure 2B). Turn this thumbscrew until the focuser
motion feels smooth and the drawtube does not slip once you
have obtained focus. If the thumbscrew is too tight the drawtube
will not move when the focus wheels are turned. It may be nec-
essary to make adjustments when the weight of your accesso-
ries changes significantly. The focuser has 61mm of drawtube
travel. A convenient millimeter scale engraved on top of the draw-
tube lets you note the focus position and return to it quickly with
a given eyepiece and diagonal combination.
The focuser is fully rotatable. Just turn the knurled focuser rota-
tion collar (
Figure 2A) counterclockwise to loosen the focuser
for rotation, then turn the collar clockwise again to secure the
focuser in the new orientation.
The telescope is equipped with a dovetail finder scope base,
which accepts any Orion finder scope as well as some other
brands. Using a finder scope, which offers low power and a wide
field of view, makes it easier to pinpoint observing subjects and
center them in the main telescope’s eyepiece.
The focuser drawtube has an accessory collar (
Figure 2A) that
accepts 1.25" accessories. For visual use you just slide the bar-
rel of the included 1.25" diagonal into the collar and then secure
it with the thumbscrew on the collar. The thumbscrew presses
against a compression ring inside the collar, which provides a
tight grip on the diagonal and prevents marring of the diagonal’s
barrel.
Attaching the Telescope to a Tripod
or Mount
The ED66-CF is equipped with a dovetail mounting bar (
Figure
2B) that can be attached to a tripod or telescope mount. For
attachment to a telescope mount, make sure the mount has a
Vixen-style dovetail saddle. Simply insert the dovetail bar into the
saddle on the mount and tighten the saddle’s locking knob. For
attachment of the telescope to a photographic tripod, note that
on the underside of the telescope’s mounting bar are two ¼"-20
threaded holes. Either of these holes will accept the standard
1/4"-20 threaded post found on most photographic tripods.
Included Accessories
The ED66-CF comes with a 1.25" correct-image 45-degree prism
diagonal and a 14mm wide-field eyepiece. The “correct-image”
diagonal has a barrel diameter of 1.25" and renders a normal
upright image. The 14mm eyepiece offers a wide 65-degree
apparent field of view and 28.6x magnification (see below for
more on magnification).
Please note that the telescope will not come to focus without
the use of the diagonal or, if you prefer straight-through view-
ing, an optional extension tube. To install the diagonal, unthread
the thumbscrew on the accessory collar until it is flush with the
interior of the adapter. Insert the diagonal and secure it with the
thumbscrew. Then insert the eyepiece into the diagonal and
secure it with the thumbscrew on the diagonal.
Calculating Magnification (Power)
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 F.L. ÷ Eyepiece F.L. = Magnification
The ED66-CF has a focal length of 400mm. The eyepiece that
comes with it has a 14mm focal length. So the magnification is
28.6x:
400 ÷ 14 = 28.6x
It is desirable to have a range of eyepieces of different focal
lengths, to allow viewing over a range of magnifications. So you
may eventually want to purchase additional 1.25" telescope eye-
pieces for more magnification options. For example, a 6mm eye-
piece would yield a magnification of 67x.
Every telescope has a useful limit of power of about 50x per
inch of aperture. So for the ED66-CF, which has an aperture of
66mm, or 2.6", that’s 130x. Keep in mind that at higher powers,
an image will always be dimmer and less sharp (this is a funda-
mental law of optics). The steadiness of the air (the “seeing”) will
limit how much magnification an image can tolerate.
Always start viewing with your lowest-power (longest focal
length) eyepiece in the telescope. After you have located and
looked at the object with it, you can try switching to a higher-pow-
er 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,
over-magnified image.
WARNING:
Never look directly at the Sun through
your telescope—even for an instant—without a
professionally made solar filter that completely
covers the front of the instrument, or permanent
eye damage could result. Young children should
use this telescope only with adult supervision.