astro-tech
www.astronomytechnologies.com
from Astronomy Technologies, PO Box 720013, Norman, OK 73070
© 2007 by Astronomy Technologies
Specifications, features, and descriptions are effective 7/1/2007, but are subject to correction and/or modification without notice and/or obligation.
Your
Astro-Tech AT90EDT ED triplet
refractor is usable for day
and night viewing, simply by adding a star diagonal and eyepiece.
Any brand of eyepiece can be used, from a 40mm for the lowest
practical magnification (15x) to a 3mm (200x) for high power use. A
2” compression ring eyepiece holder on the focuser drawtube and a
separate 1.25” compression ring eyepiece holder let you use either
1.25” or 2” star diagonals and eyepieces with no other adapter needed.
The focal length of the AT90EDT is ideal for low to medium power
wide-angle views of nebulas, open star clusters, large galaxies, and
comets. Crisp views of the Moon and planets are also routine at mag-
nifications of 120x to 200x when seeing conditions permit.
To calculate the magnification of your telescope and eyepiece com-
bination, divide the telescope focal length in mm by the eyepiece
focal length in mm. For example, a 6mm eyepiece in the AT90EDT
will give you a magnification of 100x (600mm/6mm = 100).
Astronomical Observing:
The theoretical maximum usable power
available from this telescope is 200x, although this requires a 3mm
eyepiece that provides a very dim 0.45mm diameter exit pupil. Higher
powers
are within the scope’s capabilities, but require truly excellent
seeing conditions and the patience to wait for those conditions to
make their brief and infrequent appearances.
A more practical maximum magnification for astronomical viewing
with the AT90EDT would be 150x, using a 4mm eyepiece. Keep in
mind that seeing conditions play an important role in how high a
magnification you can use on any given night. Only very good seeing
conditions (clear skies and calm air) will support viewing at 200x.
Under less than ideal conditions, lower powers in the 100x to 120x
range provide more consistently usable and pleasing images.
The widest possible field of view with a 1.25” eyepiece is about
2.8°, which can be achieved with a 15x (40mm) Plössl eyepiece yielding
a 5.97mm exit pupil. A 2” wide field eyepiece, such as the TMB 40mm
Paragon, will give a 4.53° field at the same 15x power.
The AT90EDT does an outstanding job as a wide-field astrograph
for 35mm and CCD imaging. The focuser’s 2” eyepiece/accessory
holder can be rotated a full 360° for the best photographic composi-
tion, or to put your star diagonal in the most comfortable observing
position. To rotate the eyepiece/accessory holder, loosen the chrome
lock knob on the telescope barrel just in front of the eyepiece holder
by turning it counterclockwise. Adjust the eyepiece holder to the de-
sired angle, then tighten the lock knob to temporarily lock the eye-
piece holder at the new angle. A second large chrome lock knob on
top of the scope barrel lets you lock the extra-long 140mm rack and
pinion focuser drawtube at a sharp focus for photography.
Mounting Your AT90EDT:
A stable tripod or astronomical mount
is essential for best viewing. The scope is not supplied with mounting
rings, but 114mm i. d. split rings are readily available from your Astro-
Tech dealer for installing the scope on the mount of your choice.
Terrestrial Observing:
Your AT90EDT works well for daytime
birding, nature studies, sweeping the landscape from the home with
a view, etc. – provided its 11.5 pound weight is installed on a suitably
sturdy tripod or altazimuth mount. It is also an excellent flat-field
600mm (12x) f/6.7 telephoto lens for terrestrial photography.
Generally speaking, the maximum usable daytime visual power with
any terrestrial scope is about 1x per mm of aperture (85x with a 7mm
eyepiece). Attempts to push the daytime power beyond this point
often magnify the heat waves, dust, and “mirage” in our atmosphere
to the point where the images become blurry and unusable. A 24x
(25mm) to 67x (9mm) eyepiece is usually more satisfying for every-
day high power terrestrial use than an 85x eyepiece.
Optional Astro-Tech Accessories:
Astro-Tech makes 1.25” and
2” star diagonals with state-of-the-art 99% reflectivity dielectric coat-
ings that nicely complement the performance of your AT90EDT. These
diagonals are available from your Astro-Tech dealer to provide the
maximum possible reflectivity and planetary detail. An Astro-Tech 45°
viewing angle image-erecting 1.25” diagonal is available for terres-
trial observing. An inexpensive Astro-Tech non-magnifying illuminated
multireticle finder is also available for your AT90EDT.
Collimating Your AT90EDT:
Full collimation instructions are pro-
vided in the separate collimation sheet packed with your scope.
Caring for Your Telescope Optics:
Never store your telescope
in a damp or humid environment. Avoid leaving it in a hot environ-
ment (exposed to direct sunlight on a window sill, in a car trunk, etc.)
If you must store it in high humidity conditions, put a few packets of
desiccant (silica gel or the equivalent, available from most camera
stores) in with the telescope to absorb excess moisture. If not prop-
erly stored in a humid environment, the telescope may develop mil-
dew that can damage the optics.
If dew has formed on the scope after a night of observing, allow
the scope optics to air dry at room temperature before putting the
lens cover on the scope and storing it away.
If the front lens surface becomes dusty, smeared, or shows finger-
prints or any other surface build-up, clean the lens using the follow-
ing technique. First, gently blow away any surface dust or particles
with a clean air blower (a child’s ear syringe or a photographer’s
camel’s hair brush with attached blower bulb, for example).
Using canned or compressed air is not recommended, as the pro-
pellant in the can may spit out and leave difficult-to-remove deposits
on the lens. Also, the expanding compressed air drops in tempera-
ture as it leaves the can. The cold air coming out of the tiny tube that
most compressed air cans use to direct the air flow has been known
to chill a lens to the point of spalling glass chips off the lens if pointed
at the same spot on the lens for too long.
Next, moisten a cloth with a few drops of a photographic-quality
optical cleaning solution designed for use on multicoated camera and
binocular lenses. A well-worn cotton handkerchief works well and
Zeiss and Kodak both make suitable fluids. Do not drip the cleaning
fluid directly on the lens.
Use the barely damp (not wet) cloth to gently wipe the lens sur-
face clean, turning the cloth frequently to always keep a clean portion
of the cloth in contact with the lens. Blot the lens dry with a dry
portion of the cleaning cloth or a separate cloth. Start with a clean
cloth each time cleaning is needed.
Avoid overcleaning your scope. The multicoatings on the lens are
quite hard and durable. However, frequent overzealous cleaning can
scratch the coatings if all the dust particles (which are often tiny
flecks of windborne rock) are not removed before you start pushing a
damp cloth around the lens surface. A few specks of debris on the
lens will not be visible in your images. They are not in the focal plane
and do not block enough light to measure, let alone be seen. Clean
your optics only when absolutely necessary. If you take proper care
of your scope, cleaning should rarely be needed.
Caring for Your Scope Finish:
The AT90EDT is finished in a
durable baked-on white automotive-grade paint, with grey and green
anodized trim. The long-life finish can become smudged with finger-
prints during use, but these will not harm the finish. A clean soft cloth
slightly dampened with plain water (or a little moisture from your
breath and a quick wipe with a clean handkerchief) is generally enough
to remove the fingerprints. Avoid harsh chemical cleaners or organic
solvents like benzene, alcohol, etc., as these may ruin the finish. They
can certainly affect the optical coatings if they accidentally drip or
splash on the objective lens.
Never use the telescope in the rain or in conditions where it may
get wet. The telescope is not waterproof. If your telescope acciden-
tally gets caught in the rain, immediately wipe off all water using a
clean and dry soft cloth. If your scope gets totally soaked in water, or
submerged, immediately contact your dealer for service instructions.
Do not disassemble or attempt to repair your telescope yourself, as
this violates the terms of the limited product warranty and negates
any guarantee.
Caution! Never directly view the Sun with your telescope!
Never aim your AT90EDT at the Sun without having a professionally-
manufactured solar filter mounted over the objective lens. Viewing
the Sun through the scope without the proper protection for even a
moment may result in permanent severe damage to your eyes, and
can even cause blindness. Contact your Astro-Tech dealer if you are
interested in purchasing a compatible professional solar filter.
