More Information  · Supplied Accessories

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 90 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. However, using an optional aberration-reducing minus violet filter (#CCBF) will help eliminate the faint violet halo of spurious color for the serious lunar/planetary observer (although many people find it unobjectionable in any case).

The Celestron AstroMaster 90 equatorial refractor is an optically good and mechanically solid automatic tracking 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.