The 102mm Refractor Optical Tube
The Celestron AstroMaster 102AZ is an achromatic refractor with an objective lens diameter (aperture) of 102mm, f/6.5 focal ratio, and a resulting focal length of 660mm.
AstroMaster 102AZ has the same basic optical design and shares parts that I’ve seen being used in many other Celestron telescope packages, such as the StarSense Explorer DX 102AZ, Omni XLT 102 AZ, and NexStar 102SLT.
If you don’t know, as the aperture gets larger and the focal ratio gets lower, the more chromatic aberration there is. The achromatic refractor design uses two lenses made of different glass types to control chromatic aberration, but as expected, the f/6.5 AstroMaster 102AZ shows plenty of chromatic aberration on bright targets.
When it comes to views of the Moon and planets, I figured out that the 102AZ is a little inferior to reflectors, catadioptrics, or longer f/ratio achromats. However, it is still able to reveal sharp detail on these objects and split close double stars.
As with the other AstroMaster telescopes, much of the AstroMaster 102AZ’s optical tube fittings, like the focuser body and dew shield, are plastic. However, I don’t expect this to be a huge concern.
2″ Focuser and the Scope’s Limitations in Using 2″ Accessories
The AstroMaster 102AZ has a 2” rack-and-pinion focuser. The drawtube is actually metal, but the housing is plastic. It’s a pretty good focuser and more than up to the task of handling even fairly heavy 1.25” eyepieces.
Unfortunately, the telescope can’t balance on a mount with a 2” diagonal and eyepieces due to the short length of the supplied Vixen-style dovetail bar attached to the bottom of the optical tube. In any case, I don’t foresee the 102AZ’s provided mount and tripod supporting the additional weight either.
You’d need to buy a beefier mount, tube rings, and probably a longer Vixen dovetail plate to use 2” accessories with the AstroMaster 102AZ. However, even 1.25” eyepieces can provide a very wide field with the 102AZ on account of its focal length, and the Vixen-style dovetail bar allows you to easily put the AstroMaster 102AZ optical tube on a steadier mount.
Acceptable Set of Accessories
Like the rest of the AstroMaster refractors, the 102AZ includes two 3-element eyepieces: a 20mm providing 33x and a 10mm for 66x, both with an apparent field of view of about 50 degrees.
In my usage, these eyepieces were fairly sharp and comfortable to look through. That being said, a low-power, wide-field eyepiece and one or two eyepieces for planetary viewing at higher magnifications would be good to add to your collection.
The AstroMaster 102AZ comes with a simple, easy-to-use battery-powered “StarPointer” red dot finder, which we use to aim the telescope. However, the bracket used to attach the finder to the body of the telescope tube is not very sturdy and can sometimes become bent or warped, making it difficult or impossible to align the finder with the telescope.
When aligned properly, the red dot sight is extremely easy to use to aim the 102AZ wherever you want, but if you can’t get it aligned properly, it is essentially useless.
The Celestron AstroMaster 102AZ refractor telescope is, as with many beginner telescopes sold by Celestron, equipped with a 1.25″ Amici prism diagonal, which is intended for use in terrestrial viewing by producing an image that is corrected for left-right orientation instead of being flipped like in a mirror, which is the case with an astronomical star diagonal.
This cheap diagonal has several drawbacks that make it less-than-suitable for astronomical viewing:
- Firstly, the Amici prism design creates a diffraction spike on bright objects.
- Additionally, the low-quality optical coatings on the prism and plastic body of the diagonal contribute to internal reflections, glare, and generally poor image quality.
- The prism is also undersized to the point of vignetting with some low-power eyepieces!
The Low Quality AstroMaster AZ Mount
The mount that comes with the Celestron AstroMaster AZ telescopes, such as the 102AZ, is little more than a mediocre photo tripod head attached to the same tripod as the CG-3 equatorial mount that is sold with the AstroMaster EQ telescopes. It uses a universal Vixen-style dovetail saddle to hold the optical tube, which allows you to use a different telescope on the mount if you wish.
The alt-azimuth design of the AstroMaster AZ mount, pivoting up-down and left-right, combined with its simple clutches, at first glance seems to me like a perfect match for a small, stubby wide-field refractor like the 102AZ. The tripod, while on the lightweight side and held together mostly by plastic components, is certainly up to the task of holding such a telescope.
However, since the optical tube of the telescope rides above the center of the altitude axis on the mount, I always find it unbalanced. If I try pointing the telescope high in the sky, it leads to it swinging upwards until the diagonal slams into the tripod, and aiming near the horizon causes it to droop. As such, I pretty much always have to keep the clutch on the altitude axis tightened, which impedes smooth motions.
While the AstroMaster 102AZ isn’t optically the best design for planetary viewing, the total lack of fine movement adjustment controls on the mount combined with the jerky motions of the locked-up altitude axis makes it frustrating for me to attempt using the telescope for high-magnification viewing.
A proper astronomical alt-azimuth mount, in my opinion, should keep the telescope in between or to the side of the altitude axis to prevent balance issues, as well as provide fine adjustment knobs for easier tracking at high magnifications.
Should I buy a Used Celestron AstroMaster 102AZ?
Due to the less-than-ideal nature of the Celestron AstroMaster 102AZ’s mount, I still recommend you consider a different telescope, regardless of whether you’re shopping new or used.
If you get a good enough deal on the optical tube, it may be worth attempting to find a higher-quality mount and tube rings to pair with the telescope; otherwise, there are telescope bundles with the same optics but better mounts, such as the Celestron Omni XLT 102 AZ and StarSense Explorer DX 102 AZ.
When purchasing any used telescope, it is important to check for missing accessories, damage to the objective lens, and cracks in any plastic parts, as these may indicate issues with the telescope that may or may not be repairable or alternatively lower its overall worth.
Alternative Recommendations
The Celestron AstroMaster 102AZ refractor telescope is rather expensive for what you get, and a few 4” f/6.5 refractors, while also not our top picks, are available at similar prices.
Under $350
- The Sky-Watcher Heritage 150P has significantly more light-gathering ability than the AstroMaster 102AZ and is free of chromatic aberration, as well as being ultra-portable and supported by a steady tabletop Dobsonian mount. There is also a Heritage 130P with a slightly smaller form factor and less aperture.
- The Zhumell Z114 has more light-gathering ability than the AstroMaster 102AZ and an even wider possible field of view with 1.25” eyepieces, along with a simple and sturdy design and no chromatic aberration.
- The Popular Science Celestron StarSense Explorer DX 100AZ has similar optics to the AstroMaster 102AZ but an admittedly inferior focuser. However, the mount is much higher quality and has the added bonus of Celestron’s StarSense Explorer technology to help you find deep-sky objects.
$350-$500
- The Sky-Watcher Virtuoso GTi 150P adds GoTo and automatic tracking to the already fantastic Heritage 150P but can still be aimed manually. The Virtuoso GTi 130P likewise is an upgraded Heritage 130P telescope.
- The Celestron StarSense Explorer DX 102AZ is identical to the Omni XLT 102AZ but adds Celestron’s StarSense Explorer technology; performance is similar to the DX 100AZ but the overall manufacturing quality is a bit nicer, and there’s a lot less plastic.
Aftermarket Accessory Recommendations
The 1.25″ Amici prism provided with the AstroMaster 102AZ should be replaced with a better star diagonal. As previously mentioned, the telescope cannot balance with a 2” diagonal, so I would recommend sticking with a 1.25” unit. A prism-star diagonal can induce slight aberrations at f/6.5 but is much cheaper than a good dielectric mirror diagonal and will remove the vignetting, glare, ghost images, and sharpness problems that the Amici tends to cause.
A 32mm Plossl eyepiece provides 20x magnification with the AstroMaster 102AZ and the widest possible true field achievable in a 1.25” format eyepiece, about 2.6 degrees across.
At the other end, a 6mm “goldline” eyepiece will produce 108x, ideal for planetary viewing and about as high of a magnification as either the telescope or its mount can handle.
While a bit of a splurge for an inexpensive and relatively flawed telescope, using a UHC nebula filter with the AstroMaster 102AZ can enhance your view of nebulae and reveal more detail within them. You can also use the filter with another telescope in the future. The Orion 1.25” UltraBlock filter is my top pick for a nebula filter and pairs nicely with the AstroMaster 102AZ. You could also get the 2” version and screw it onto the provided 1.25” adapter to future-proof yourself for a larger telescope.
What can you see with Celestron Astromaster 102AZ?
The Celestron AstroMaster 102AZ is best suited for viewing large, bright deep-sky objects such as big and colorful open star clusters, many of which can be seen in cities. Examples of these types of objects include the Double Cluster in Perseus or the Pleiades (M45) in Taurus.
Globular star clusters and most planetary nebulae, however, are beyond the light-gathering or resolving capabilities of the AstroMaster 102AZ, especially from more light-polluted locales. However, the Ring Nebula (M57), the Dumbbell (M27), and the Blinking Planetary are recognizable, as is the faint Helix Nebula with a UHC nebula filter and fairly dark sky conditions.
With only 4” of aperture, most galaxies will appear as smudges without much detail, even under dark skies without too much light pollution. However, the brightest ones, such as M31, M64, or M82, show dust lanes, and I can also see galaxy groups and clusters, or companions to larger galaxies, such as those orbiting M31 (Andromeda).
Bright emission nebulae such as Orion (M42), the Swan (M17), and the Lagoon (M8) are fantastic from suburban or dark skies, especially if I use a UHC filter. The North American Nebula and Veil Nebula are spectacular with a UHC filter and a dark sky with the AstroMaster 102AZ.
Planetary viewing is limited by the AstroMaster 102AZ’s chromatic aberration and mount.
- The phases of Mercury and details on Mars are tough to see at all.
- The Moon looks spectacular, however, and the phases of Venus are easy to see.
- Jupiter’s moons and some detail in the giant planet’s colorful cloud belts are visible, though the Great Red Spot and the disks or shadows of the moons are a little difficult to make out.
- The rings of Saturn look spectacular, and I’m able to also see the Cassini Division in the rings, Saturn’s cloud belts, and a few moons.
- Uranus and Neptune are barely distinguishable from bluish stars with the limited resolving power of the 102AZ, and their moons are far too dim to spot.
- Pluto requires a much larger telescope than the 102AZ to observe it as well.
