Overview Of Astromaster 76EQ Optical Tube Assembly
The AstroMaster 76 optical tube is a 76mm (3-inch) f/9.2 Newtonian with a spherical primary mirror. A spherical primary in a larger, faster telescope such as the 130mm f/5 AstroMaster 130 will cause significant lack of sharpness and definition and is thus unsuitable for an astronomical telescope, but a 76mm f/9 sphere deviates only very slightly from a parabola, so it works just fine.
The only drawback, optically, of the AstroMaster 76 is its diminutive size. By the time one accounts for light loss from the mirrors and the secondary mirror’s obstruction, the AstroMaster 76 performs no better than a 60mm refractor. However, the 76EQ does offer the advantages over a refractor of no chromatic aberration and a shorter focal length – the former giving it better planetary/lunar performance, all other things being equal, and the latter giving it a wider field of view and lower power with a given eyepiece.
The AstroMaster 76 has a decent red dot finder mounted to the front of the optical tube assembly, and a more than adequate 1.25” rack and pinion focuser. Both the primary and secondary mirrors can be collimated – which is a feature that although required, somehow isn’t always available with cheap small Newtonians.
One annoying drawback of the AstroMaster 76 is that the focuser drawtube unnecessarily pokes into the light path when it is racked all the way in. Usually it’s racked out enough for this to not be a problem, but with some eyepieces it may eclipse the incoming light from hitting the scope’s primary mirror by quite a bit. If this bothers you, it’s quite easy to remove the drawtube, chop the offending portion off with a hacksaw, and re-install it with absolutely no negative impact on the telescope’s functionality.
The other fault of the optical tube is that it has an extremely short dovetail bolted directly to the tube. There is thus no way to rotate the tube to a more comfortable position, nor balance it if you are using heavy eyepieces/accessories.
Like all other AstroMaster Newtonians the AstroMaster 76 comes with a cheap, narrow-field 20mm eyepiece. This eyepiece really provides too much power (35x) to be a “low-power” eyepiece for a 76mm telescope and also has a narrow, straw-like field of view. Furthermore, its useless erecting optics and cheap coatings absorb a lot of light and degrade the image quality. We would recommend replacing it with a 32mm or 25mm Plossl as soon as possible to get the most out of this telescope.
The other included eyepiece is a 10mm Kellner, which provides 70x. It’s a pretty decent eyepiece, albeit largely made of plastic.
The mount supplied with the AstroMaster 76EQ is referred to in some literature as the “CG-2” but it is identical to the mount supplied with the larger AstroMasters which Celestron terms the CG-3.
The CG-3 is overkill for the featherweight 76mm Newtonian optical tube, but certainly does a great job. The scope is rock-solid and I have zero complaints about stability.
The CG-3 has flexible slow-motion cables – there is only one for the right ascension axis, however, and you’ll have to swap it from one side of the mount to the other depending on which half of the sky you’re viewing. The mount also is of course capable of taking other telescope optical tubes, but a different optical tube would likely cost more than the entire AstroMaster 76EQ unit.
The CG-3 can be motorized with Celestron’s Logic Drive for hands-free tracking. Forget astrophotography, though – any kind of camera will make the scope top-heavy and there’s no way to balance it, in addition to the fact that this is an f/10 scope on a relatively simple mount with an only partially metal focuser.
For the same price as or a little more than that of the AstroMaster 76EQ, we’d probably recommend a tabletop scope: Either the Zhumell Z100 or Orion SkyScanner, essentially identical scopes with a bit more aperture and far superior accessories. If you can expand your budget, the Zhumell Z114 is even better.
Aftermarket Accessory Recommendations
The only accessory that the AstroMaster 76EQ really needs is a 25mm Plossl eyepiece (28x). This will work far better as a low magnification eyepiece than the included 20mm erecting eyepiece. A 2x Barlow to bring the 10mm eyepiece up to 140x also might be a good idea.
Apart from simple phone shots, forget any kind of astrophotography with the AstroMaster 76EQ. The scope is too small in aperture to do useful work with a CCD camera for planetary imaging (a CCD would also cost more than the entire telescope), and a DSLR will strain the focuser and mount as well as render the telescope unable to balance properly.
For a sub-$200 telescope, though, this is all to be expected.
What can you see?
The 76mm aperture of the AstroMaster 76EQ is only enough to show you the brightest deep-sky objects, but it will do a reasonably good job on the Moon and planets. With the AstroMaster 76EQ, expect to see:
- Mercury’s phases, with effort and luck
- Venus’ phases
- Lots of detail on the Moon
- One or two dark patches on Mars when it’s at opposition every two years
- Jupiter’s moons, cloud belts and Great Red Spot
- Saturn’s rings, its moon Titan, and maybe the Cassini Division and some banding on the planet itself with good seeing
- Uranus and Neptune as turquoise and azure dots
- The Orion Nebula, the Ring Nebula, M13, the Pleiades, and a couple dozen of the other brightest deep-sky objects
- Many double stars