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Celestron 21064 AstroMaster 90 Refractor Telescope – Review

Last Updated: 29.11.21


Main technical features


The perfect telescope for beginners, the Celestron 21064 AstroMaster 90 is designed for both celestial and terrestrial viewing applications. It is an equatorial refractor that provides a step up from a 60mm refractor starter model while being priced unbelievably close to its economy toy-store counterpart. Made for those ready for serious observing of the solar system and beyond, this model provides 125 percent greater light collecting capability so even deep-sky images come out brighter and with 50 percent greater resolution compared to 60mm telescopes while guaranteeing higher quality features and optical performance.

The top notch optical system comprises all-glass optical components boasting high-transmission optical multi-coatings to ensure enhanced image clarity and brilliance that the avid observer will fully appreciate. Get the sensibly large 3.5-inch aperture bundled with reduced image diffraction for deep space observation. Light-gathering capability is 165 times more than even your sharp naked eye vision. Get 1000mm focal length f/11.1 thanks to the two-element crown working well with the flint glass achromatic doublet system, with no plastic lenses of any kind.

The dew shield is threaded onto the front end of the objective lens and serves as an extension of the optical tube. The 1.25-inch star diagonal with 90-degree viewing angle provides correctly oriented mirror image views. The rack and pinion 1.25-inch focuser is solidly constructed and features dual focusing knobs to enable precise image tuning control with just one hand, whether left or right. The focus knobs are appropriately sized for easy operation even with gloved hands during unforgiving weather. On the optical tube is the quick-release dovetail bar that goes nicely into the mount’s dovetail slot. Installation and firm locking of the optical tube can be done in seconds using the tool-free knob on the mount.


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In-depth information


Able to resolve details 13 times smaller than what you can perceive with your naked eye, this telescope provides sharp details with its two eyepieces: a 10mm for 100X and a 20mm for 50X maximum magnification. This enables you to view numerous solar and lunar system details that a more inferior scope will be unable to show you. Enjoy sharpness and high contrast to bring planets to life in the eyepiece. The refractor design is child-friendly so maintenance is hassle-free while supporting use for extended times. Get clear and brilliant images of the moon and planets via the fully coated 90mm lens. This large lens lets more light through when observing distant objects including Saturn’s rings and Jupiter’s moons. This is a mechanically solid astronomical telescope that won’t break the bank.

Featuring multi-coated optics, this telescope enables you to enjoy crisp and clear images. The permanently-mounted Starpointer finder scope allows easy locating of celestial targets by working optimally with the German equatorial mount with setting circles. The optical multi-coatings offer high transmission for great clarity and brightness of images so you can view vivid and greatly resolved globular star clusters, with the contrast in colors of numerous binary systems rendered exquisitely well. The two-element objective lens is designed with multiple layers of vacuum-deposited anti-reflective material on all its air-to-glass surfaces to ensure fantastic contrast and high light transmission.

The rugged pre-assembled tripod this telescope ships with enables astrophotography use with a compatible T-mount adapter. The tripod comes with 1.25-inch steel tube legs that give it a stable and strong secure platform. For storing accessories conveniently, this model comes with a deluxe accessory tray. The dovetail mount enables quick placement of the optical tube. The dew shield delays the formation of condensation on the lens particularly in cold weather, thereby enabling you to have an uninterrupted observation experience while improving contrast for daytime terrestrial observing. The rack and pinion focuser enables easy operation while ensuring precise tuning of viewed images. When looking at the sky, you are given comfortable viewing thanks to the 90-degree star diagonal that provides properly erect images using the high-power eyepiece. This means no reversed images, with stars also appearing in the same orientation through the finder as they appear on star charts.


Known issues

When looking through the scope at night to view extremely brilliant objects, there may be a bit of chromatic aberration, which is inherent in all achromatic refractor scopes. In addition, tracking and centering objects may be challenging on the ground because of the equatorial mount. The erect image eyepiece serves best for lunar observations.


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Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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