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The Meade ETX-90AT Telescope’s Optical System . . .

• Maksutov-Cassegrain optical tube: 90mm (3.5") aperture, 1250mm focal length, f/13.8 focal ratio. The meniscus corrector lens is Grade-A BK7 optical glass. The primary mirror is Pyrex. Guaranteed diffraction-limited optical performance.

• Fully multicoated optics: Anti-reflection UHTC (Ultra High Transmission Coatings) multicoatings on both sides of the BK7 optical glass Maksutov corrector lens, plus high light transmission enhanced aluminum multicoatings on the mirrors, provide a 16% increase in light throughput compared to standard coatings. UHTC multicoatings effectively add the equivalent of more than a quarter of an inch of extra light-gathering aperture to the performance of a scope with standard coatings, but at no increase in size or weight.

• Excerpts from a review of the optics: Sky & Telescope magazine said, "The optics in our test telescope were excellent . . . Familiar with how rarely 8-inch and larger telescopes experience moments of good seeing, I was pleasantly surprised by how often the atmosphere served up diffraction-limited conditions for the smaller aperture ETX-90. You don't see more detail with the small scope, but the sharp images are very satisfying and a frequent reminder of the excellent optical quality.
      "The Moon was beautiful at any magnification, with black shadows contrasting sharply with illuminated features along the terminator. Venus appeared dazzlingly white with no color fringes except those caused by atmospheric refraction. Like Venus, Jupiter was low in the January evening sky, but several bands were easily seen on the planet's disk.
      "Saturn was very impressive. As the planet snapped into focus in the supplied 26-mm (48x) eyepiece, I could easily see the rings' Cassini Division and several bands on the ball of the planet. Even at this modest magnification the moons Titan, Rhea, and Dione were clearly visible, and Tethys became evident when the power was increased to 156x.
      "The bottom line is that the ETX-90 showed me everything I could expect from an instrument of its size."

  While the ETX-90AT’s aperture limits the number of deep sky objects visible, those that are within its magnitude 11.7 light grasp stand out crisply against a dark sky, particularly multiple star systems, globular clusters, and compact planetary nebulas.

• Dust covers: Dust covers protect the meniscus lens and seal the Cassegrain focus on the rear cell.

• Finderscope: The supplied straight-through non-magnifying illuminated red dot finder seems to projects a red dot of light on the sky (not visible in the eyepiece) to show you where the scope is pointing at all times.

• Star diagonal: Built-in first surface flip-mirror. For astronomical observing, the internal flip-mirror directs the image to the eyepiece holder at the top of the scope. Touch a lever, and the flip-mirror redirects the image through the Cassegrain focus at the rear of the scope to an optional #64 T-adapter and T-ring for lunar or terrestrial photography, or to an optional #932 45 degree viewing angle image-erecting diagonal for upright and right-reading terrestrial viewing.

• Eyepiece: 1.25” 26mm Series 4000 Super Plössl (48x). The eyepiece field of view is 1.04 degrees, more than twice the diameter of the full moon.

The Meade ETX-90AT Telescope’s Mechanics and Electronics . . .

• Dual fork arm altazimuth mount: The optical tube is aluminum. The rear cell, fork arms, and drive base are durable metal-reinforced injection-molded plastic that helps keep the cost of the 90AT so very reasonable. While the molded parts of the 90AT are quite rugged, a little extra care in setting up and using the scope might be prudent.
      There are three rubber feet on the base of the scope. These allow the 90AT to be placed on a suitably sturdy tabletop or flat surface for casual computerized observing without having to set up the supplied full length field tripod.
      The mount includes built-in right ascension and declination DC drive motors for tracking objects under the control of the supplied AutoStar computer. The motors are powered for up to 20 hours by eight AA batteries (not supplied) that fit into an internal battery compartment in the telescope base. They can also be powered by an optional #RCXAT AC adapter for powering the scope from household AC or by an optional #607 cigarette lighter plug cord for powering it from your car’s cigarette lighter or a 12 volt rechargeable battery pack in the field.
      When used in the default altazimuth mode, the supplied AutoStar computer hand control moves the scope in any of four directions (right/left and up/down) at any of nine speeds. The speeds range from 2x the sidereal rate for guiding, up to 5 degrees per second for locating objects and slewing, plus the sidereal rate for tracking objects. No manual slow motion controls are provided – or needed. When set up on the supplied tripod for equatorial (polar) operation using the tripod’s built-in equatorial wedge, the AutoStar computer converts the right/left, up/down altazimuth directions to motions in right ascension and declination to correspond with the coordinates of objects on the celestial sphere.

• AutoStar computer hand control: The standard equipment #497 AutoStar computer automatically slews to, and tracks, more than 30,000 near and deep space objects (although not all will be visible due to the 11.7 limiting magnitude of the scope’s 3.5" aperture). The objects include all 110 of the Messier objects; the complete 5386-object IC catalog, the complete 7840-object NGC catalog, the complete 109 object Caldwell catalog of the best objects for small telescopes; 16,800 stars from the SAO catalog including double starts, variable stars, and other stars of special note; the planets; 26 of the brightest asteroids; 15 periodic comets; 50 earth-orbiting satellites; the centroids of all 88 constellations; plus user-defined objects and guided tours around the sky.
      The AutoStar hand control gives you a digital readout of r. a. and dec coordinates; scrolling information about the object being viewed; plus the results of calculations about sunrise, sunset, moonrise, moonset, moon phases, solar eclipses, lunar eclipses, the minimum of Algol, and more. Hypertext links on the AutoStar screen display define many of the terms used in the computer (there's more than one megabyte of compressed text stored in the AutoStar.) Built-in guided tours of the sky are tailored to the day of the year you are observing. They direct you to showpiece objects, including the Moon and any planets then visible. Most of the tour objects are accompanied by descriptions scrolling across the AutoStar display (the description of Algol, for example, is over 300 words long). The Moon has different descriptions based on its phase, and prominent features near the terminator are highlighted.
      Pointing accuracy of the AutoStar computer is good in either mode. The Sky & Telescope review noted that they used the "AutoStar's internal catalog and the Go To function to slew to more than a dozen bright stars scattered around the sky. All but one lay well within the 1 degree field of the 26-mm eyepiece"

• AutoStar computer operation: The operation of the ETX-90AT is simplicity itself. On-screen operation instructions guide you through setup and use of the AutoStar and a help function is only a keystroke away. Once you mount the scope on its tripod, aim the scope north and level the optical tube. Enter your observing location’s latitude and longitude into the AutoStar computer hand control. This needs only to be done once, as the scope will keep the location in its memory, as well as that of several other favorite observing sites that you can call up at will. Enter the time. The ETX-90AT will orient itself to the sky and slew at 6.5 degrees per second to the first of two alignment stars. If that star is not precisely centered, a touch or two on the AutoStar hand control directional push buttons quickly centers it. Do the same with the second alignment star the scope moves to and you’re ready to observe. That's it!
      It takes only a few minutes to begin observing. For the rest of the evening, a computer in the AutoStar controls the scope’s altitude and azimuth motors to keep you precisely centered on whatever you aim at, for as long as you want to observe.

• Adjustable height tripod: The supplied full-length Meade #884 Deluxe Field Tripod provides a rigid mounting platform for virtually any observing application, astronomical or terrestrial, and can be used for either standing or seated observing. The #884 has tubular chromed steel legs and is adjustable in height from 26" to 44" when used in the altazimuth mode. It has a built-in equatorial wedge with an integral latitude scale and no-tool latitude (altitude) adjustment for use at any observing latitude between 20° and 90°. The 90° (altazimuth) position is for terrestrial observation and for quick set-up astronomical observing. Setting the wedge tilt plate to your observing latitude and aligning the scope on the celestial pole allows more accurate object location and sidereal rate tracking, but takes a little more time to set up.
      The ETX attaches to the tripod in seconds using two thumbscrews in the wedge tilt plate. The thumbscrews are tethered and spring-loaded so they can’t be lost in the field. The spreader bar that holds the legs open is spring-loaded as well, so setting up and taking down the tripod takes only a few seconds. There are six 1.25” diameter holes cut into the spreader bar to hold 1.25” eyepieces. The tripod comes with a padded Cordura-style carrying case with carry handle, shoulder strap, and an external zippered pocket for the spreader bar.

• AutoStar Software Suite: This new software package is included as standard equipment with the ETX-90AT. It is designed to integrate the telescope with your PC or laptop computer for an enhanced range of performance features. The AutoStar Software Suite includes a planetarium program with a database of 19,000,000 stars and deep space objects for display on your computer screen. It includes all the standard planetarium program features for stand-alone use when nights are cloudy.
      In addition, if you connect the scope to your computer (using the supplied cable), the program lets you click on objects in the sky map displayed on the computer screen and have your telescope automatically slew to those objects. You can automatically generate AutoStar Tours of favorite objects with a simple point and click. The software lets you control all AutoStar functions from your computer or laptop. You can use it to create observing lists and download them to the AutoStar for use in the field when you don’t have your computer or laptop with you. You can use it to control your telescope remotely via the Internet. “Talking Telescope" software (included) converts AutoStar text displays to synthesized speech through your computer speaker. An AutoStar Update Tool keeps your AutoStar current by downloading the latest system firmware updates and comet, asteroid, and satellite data over the internet from Meade’s website.