Your
The focal length of the AT90EDT is ideal for low to medium power
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
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
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
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
Using canned or compressed air is not recommended, as the pro- pellant in the can may spit out and leave
Next, moisten a cloth with a few drops of a
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
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
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© 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. |