The Celestron AstroMaster 90 equatorial refractor is a big step up from a 60mm refractor "starter scope." While it is surprisingly close to many economy 60mm scopes in price, it is far above them in features, quality, and optical performance.
This Celestron AstroMaster 90EQ is a 3.5" (90mm) aperture equatorial refractor. It is surprisingly economical, considering the performance and features you get versus the price you pay.
Many beginners start out with an inexpensive 60mm (2.4") toy-store refractor, although too often they find to their dismay that a scope that size is too small for serious observing outside the solar system. For not much more money than a 60mm scope, this 90mm Celestron telescope gives you 125% more light gathering for brighter deep space images (and a full 50% higher resolution than a 60mm for revealing planetary details!)
The construction of the optical system is first rate, as the AstroMaster has all-glass optical components, with high transmission optical multicoatings for enhanced image brightness and clarity. For the observer whose interests are the brighter solar system and deep space objects, the AstroMaster 90 equatorial has a lot to offer. Its 3.5" aperture has a light grasp 165 times that of the sharpest eye for nighttime and twilight use. Its sensibly large aperture and diffraction-free images make it surprisingly good for much deep space observing. Binary stars and globular star clusters are particularly well-resolved and vivid, with the contrasting colors of many binary systems showing nicely. The brighter nebulas and galaxies stand out against a darker sky background than is possible in a comparably-priced reflector with its light-scattering diagonal mirror.
The AstroMaster 90EQ can also resolve details thirteen times smaller than you can see clearly with your unaided eye. Combine that sharpness with its two eyepieces (a 20mm for 50x magnification and a 10mm for 100x), and you have the ability to see many, many lunar and solar system details that are simply invisible in a lesser scope. Its views of subtle lunar and planetary details are sharp and high in contrast, bringing the planets to vivid life in the eyepiece.
Some chromatic aberration is present in the scope when viewing very bright objects at night, as it is in all achromatic refractor telescopes.
The Celestron AstroMaster 90EQ equatorial refractor is an optically good and mechanically solid astronomical telescope at a very reasonable price. It may well be the ideal telescope for you if you're a beginning astronomer on a budget who wants more than a toy telescope.
This Telescope's Optical System . . .
Refractor optical tube: 90mm (3.5") aperture. 1000mm focal length f/11.1 two-element crown and flint glass achromatic doublet. No plastic lenses.
Multicoated optics: The two-element objective lens has multiple layers of vacuum-deposited antireflection materials on all air-to-glass surfaces for the highest light transmission and good contrast.
Dovetail mount: A quick-release dovetail bar on the optical tube fits into a dovetail slot on the mount. The optical tube can be installed and locked firmly in place in seconds using a single no-tool knob on the mount.
Dew shield: A dew shield (an extension of the optical tube that's threaded onto the front of the objective lens) slows the formation of dew on the lens in cold weather. This extends your undisturbed observing time. It also improves the contrast when observing objects on the ground during the day.
Rack and pinion focuser: The well-made 1.25" focuser has dual focusing knobs for precise image control with either hand. The good-sized focus knobs are easy to operate, even while wearing gloves or mittens in cold weather.
Star diagonal: The 90° viewing angle 1.25" star diagonal (eyepiece holder) allows comfortable viewing when looking overhead at the sky. It provides erect mirror image views (objects are reversed left for right) with the supplied high power eyepiece. This is not a problem when observing the stars and planets, but may be disconcerting during terrestrial observing, as printing (license plates, the names on boats, etc.) will be backwards. For most nature studies this isn't a problem, though, because a duck still looks like a duck whether he's facing left or right. An optional #6329 45° viewing angle image-erecting diagonal is available if right-reading images are essential. It gives you correctly oriented images and more comfortable extended terrestrial observing.
Two eyepieces: You get a high power 1.25" 10mm (100x) eyepiece and a low power erect image 1.25" 20mm (50x) with a 1° field of view (twice the diameter of the full Moon). The 50x erect image eyepiece lets you use the 90EQ terrestrially, as its images are not reversed as they are with most refractors. However, the equatorial mount will make it difficult to center and track objects on the ground. The erect image eyepiece will probably serve you better for lunar observing, as it will show you a familiar image of the Moon, oriented as you see it with your unaided eyes or binoculars. Both eyepieces are of a higher quality optical design than you'll find in most other telescopes in this price range. They have antireflection coatings on their lens surfaces for sharp images and very good contrast. Instead of providing low quality eyepieces that give unrealistically high (and generally unusable) 200-300x magnifications as most economy telescope manufacturers do, Celestron has chosen to provide higher quality eyepieces with sensible powers you can use and enjoy every time you take your AstroMaster 90EQ out to observe.
Red dot finder: A straight-through red dot illuminated finder allows easy non-magnified views of the sky and ground, with a projected red dot of light showing exactly where the scope is pointed at all times. Stars appear through the finder in the same orientation that they appear on star charts. There's no confusing reversal and inversion of the image as you'll find in an ordinary straight-through finderscope.
This Telescope's Mount . . .
Equatorial mount: The scope's sturdy CG-3 equatorial mount is designed for astronomical observing. By aligning the mount on the north celestial pole, you only need to turn one slow motion control knob to follow planets and stars as they travel across the sky. An economical optional #MDASTRO battery-operated right ascension motor drive takes the slow motion control out of your hand and makes following the stars a no-hands operation. Two counterweights on the opposite side of the mount from the telescope tube balance the weight of the optical tube and make it easy to move the scope effortlessly from one part of the sky to another. No tools are required to adjust the position of the counterweights to quickly and precisely balance the optical tube. A micrometer control lets you adjust the altitude of the scope mount to match your latitude for fast alignment on the north celestial pole with no tools required.
Setting circles: Setting circles (graduated scales marked in either hours and minutes or degrees) are provided in both right ascension (the east/west position of objects in the sky measured in hours and minutes) and declination (the north/south position measured in degrees). These allow you to align the scope on the approximate position of an object in the sky by using its r. a. and dec coordinates from a star chart or atlas - before you search for it in the finderscope and eyepiece. Setting circles can reduce the time it takes for you to find the fainter and more difficult deep space objects.
Manual slow motion controls: There are two slow motion control knobs conveniently positioned on the mount so they are easy to reach while observing. One controls the scope's motion in right ascension (the east/west direction in the sky). Turning this knob enables you to follow the motion of celestial objects as they travel from east to west across the sky. The second controls the scope's motion in declination (the north/south direction in the sky). Turning this knob enables you to correct for any north/south drift a celestial object may take as it moves across the sky, due to an improper alignment of the scope on the north celestial pole when you first set it up. The two controls combine to give you complete access to any part of the sky. They give you the ability to star hop from a known object to any other object by using a star chart. They let you center objects in the field of view, then track them effortlessly with only an occasional quick turn of the r. a. knob. As mentioned above, an optional motor drive is available for hands-free tracking.
Tripod: The lightweight pre-assembled tripod has 1.25" diameter stainless steel legs to provide a rigid and stable observing platform. It easily adjusts in height with no tools needed. The no-tool lock knobs that adjust the leg height of the tripod are on the inside of the legs so they won't snag on clothing in the dark, a thoughtful touch that's sure to be appreciated. Spreader bars lock the legs firmly open when the tripod is set up. The tripod includes a convenient accessory tray that attaches to the spreader bars to hold your eyepieces and accessories close at hand and up out of the dew-soaked grass.
Two year warranty: As an expression of Celestron's confidence in the quality of their products, the AstroMaster 90 is protected by Celestron's two-year limited warranty against flaws in materials and workmanship.
