The Celestron AstroMaster 90 altazimuth refractor is a good-value medium aperture refractor for the terrestrial observer or casual astronomer. It is ideal for tracking boats, cars, and wildlife on the ground and scanning the Moon, planets, and star clusters in the night sky.
The Celestron AstroMaster 90AZ altazimuth refractor is a good choice for a beginning astronomer who also has an eye for nature. This sensibly-priced medium aperture refractor optical system is a good way to begin your journey into the night sky, as well as exploring nature during the day. It provides you with detailed high-contrast views of the Moon and planets in the heavens, as well as sharp views of birds and animals across a lake or across the way.
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. The mount has a convenient pan handle, like the control handle on a camera tripod, for guiding the scope around the skies or the landscape. A built-in clutch makes operating the well-balanced scope with the pan handle smooth and easy. The scope assembles in only a minute or two, with no tools required.
For the astronomical observer whose interests are the brighter solar system and deep space objects, the AstroMaster 90 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 90AZ 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 celestial and terrestrial objects that are simply invisible to the unaided eye. 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.
Once you have scanned your way through the solar system and the Milky Way, you can use the AstroMaster to look at things closer to home. The altazimuth mount will let you easily track objects on the ground and allow you to get a sharply-detailed closer look at nature and your surroundings. The AstroMaster 90 is an economy-priced scope that can open new worlds for you, both on the ground and in the sky.
This Telescope's Optical System . . .
Refractor optical tube: 90mm (3.5") aperture. 1000mm focal length f/11.1 achromatic doublet lens with all-glass optics. 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). 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 1.25" 20mm (50x) with a 1° field of view (twice the diameter of the full Moon). Both eyepieces have antireflection coatings on their lens surfaces for sharp images and good contrast.
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.
This Telescope's Mount . . .
Altazimuth mount: The altazimuth mount with camera tripod-style pan handle provides right/left and up/down motions. This is suitable for casual astronomical observing, and will let you easily track objects on the ground to allow you to get a closer look at nature and your surroundings. An adjustable tension clutch knob at the base of the mount allows you to lock the tube in place or to adjust the drag on the scope during right/left motions. This lets you control how smoothly the mount moves as you move the tube left or right to follow objects moving across the sky or on the land. A simple twist on the pan handle locks the scope in place up and down, as well as letting you adjust the drag on the scope to set the travel smoothness when adjusting its position vertically. The optical tube is well balanced, but keeping your hand on the pan handle at all times when the clutches are unlocked would be a sensible safety precaution.
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 for standing or seated observations through the telescope. 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. 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.
Two year warranty: As an expression of Celestron's confidence in the quality of their products, the AstroMaster is protected by Celestron's two-year limited warranty against flaws in materials and workmanship.
