Choosing An Eyepiece; The Barlow Lens - Meade DS-2090 Instruction Manual

Intensity Slider
Fig. 13: Red Dot Viewfinder
intensity slider. Slide the
switch to the right to turn on
the viewfinder. The switch
provides two levels of inten-
sity for the red dot.
NEVER
point the
telescope
directly at
or near the Sun at any
time! Observing the
Sun, even for the
smallest fraction of a
second, will result in
instant and irre-
versible eye damage,
as well as physical
damage to the tele-
scope itself.
Fig. 15: 25mm and
9mm eyepieces.
5. Check this alignment on a celestial object, such as the Moon or a bright star, and make
any necessary refinements.

Choosing an Eyepiece

A telescope's eyepiece magnifies the light gathered by the optical tube. Each eyepiece has a
focal length, expressed in millimeters, or "mm." The smaller the focal length, the higher the mag-
nification. For example, an eyepiece with a focal length of 9mm has a higher magnification than
an eyepiece with a focal length of 25mm.
Your telescope comes supplied with a low-powered 25mm or 26mm eyepiece which gives a
wide, comfortable field of view with high image resolution. Always begin your observations with
this eyepiece.
Low power eyepieces offer a wide field of view, bright, high-contrast images, and eye relief dur-
ing long observing sessions. After an object is located and centered in the eyepiece, try switch-
ing to a higher power eyepiece to enlarge the image.
NOTE: Viewing conditions vary from night-to-night and from site-to-site. Turbulence in
the air, even on an apparently clear night, can distort images. If an image appears
fuzzy and ill-defined, return to a lower power eyepiece for a more well-resolved image.
The power, or magnification of a telescope is determined by the focal length of the telescope
and the focal length of the eyepiece being used. To calculate eyepiece power, divide the tele-
scope's focal length by the eyepiece's focal length. For example, you may wish to use a 25mm
eyepiece with the DS-2000 model DS-2114S. Look up the focal length of the DS-2114S under
SPECIFICATIONS: DS-2114S
focal length is listed as 1000mm.
Telescope focal length
Eyepiece focal length = Eyepiece power
1000 Ö 25 = 40
The eyepiece power, or magnification is
therefore 40X (approximately).

The Barlow Lens

Some Meade telescopes include a power
multiplier called a Barlow lens. Consisting of
a lens mounted in a 4"-long (10cm) tube,
the Barlow doubles or triples the power
obtained when an eyepiece is used alone. In
the example above, a 25mm eyepiece
results in 40X magnification with the DS-
2114S telescope; when this same eyepiece
is used in conjunction with a 2x Barlow lens,
power is doubled to 80X. To use the Barlow,
insert it into the diagonal prism (refractor
models only) or eyepiece holder, followed by
the eyepiece.
, page 32. The
divided by
Can you ever have too much power? If you're
referring to eyepiece power (magnification),
yes, you can! The most common beginner's
mistake is to "overpower" a telescope by using
too high of a magnification, which the tele-
scope's aperture and atmospheric conditions
cannot reasonably support. Keep in mind that
a smaller, but bright and well-resolved image
is far superior to one that is larger, but dim and
poorly resolved (see below). Powers above
200X should be employed only under the
steadiest atmospheric conditions.
Autostar can calculate the best eyepiece for
you to use. Try out the "Eyepiece Calc" feature
in the Utilities menu.
Most observers should have three or four
additional eyepieces to achieve the full range
of reasonable magnifications possible with the
DS-2000
ACCESSORIES," page 28.
Fig. 14a & 14b: Jupiter; example of too much
magnification.
13
DS-2000 TIPS
Too Much Power?
telescopes. See "OPTIONAL