Inspire 100AZ’s Optical Tube
The Inspire 100AZ’s optical tube is a 100mm f/6.6 refractor with a focal length of 660mm-or so they say; in fact, they just stopped down a 102mm f/6.5 slightly due to the design of the front of the telescope being slightly different from the norm.
This slight design quirk has basically no effect on the performance of the telescope, but it is of note as it indicates some other differences from the norm. The entire front end of the Inspire 100AZ is black moulded plastic, including the dew shield, sometimes referred to as a “lens hood”. This dew shield is really a bit short for the telescope, and the injection-moulded plastic surface on the inside is quite shiny. Installing some adhesive-backed black velvet “flocking” or attacking the dew shield with coarse sandpaper and flat black paint does wonders to improve contrast and reduce glare, particularly when observing bright objects or under light-polluted skies, which so many of us are unfortunate enough to be stuck in.
Being a larger achromat with a relatively fast focal ratio (by refractor standards, anything below f/10 is considered fast), the Inspire 100AZ does suffer from some chromatic aberration, or “false colour”, which manifests itself as an obnoxious purple halo around bright targets such as the Moon, Jupiter, Venus, and many double stars. Some people will spend thousands of dollars on an ED triplet apochromatic refractor to get basically the same views as the Inspire 100AZ without the colour; you can simply choose to ignore it. Though it does prevent one from getting the sharpest images possible of the Moon and planets, for 99% of viewing, the Inspire 100AZ’s optics do just fine. You really need not worry.
The focuser on the Inspire 100AZ is a bit unusual in that an entire pointless piece of the rear cell slides along with it. Otherwise, it’s a standard all-plastic 1.25” rack-and-pinion unit. There’s also a “focus micrometre” on the side – a small window lets you see a dial indicating a number (between 1 and 20) which lets you “set” the focus, which at best could be used as an extremely counterintuitive reference to save half a second on focusing with individual eyepieces. However, the “micrometre” is tiny, positioned on the side of the telescope, and not illuminated in any way, so it is a functionally useless decoration. Why Celestron elected to include this, we simply don’t know. The focus knobs are also unusually small so as to not obstruct this dial, which makes fine focusing the 100AZ slightly more difficult than it otherwise would be.
Most other 100/102mm refractors, like the Inspire 100AZ, feature a 2” focuser without any weird design hangups, and it’s a shame the Inspire lacks one, as it would really open up possibilities for wide-field viewing of deep-sky objects.
The Inspire 100AZ attaches to its mount with a short Vixen-style dovetail bar attached to the bottom of the tube, and its finder bracket accepts most standard finderscope bases.
The Inspire 100AZ includes two standard, interchangeable 1.25” eyepieces: a 20mm Kellner providing 33x magnification and a 10mm Kellner providing 66x magnification. These are all-plastic in construction (the lenses are, thankfully, glass) and will work well. You’ll probably want additional eyepieces to get the most out of this telescope, however—both at the low power end for wide-field vistas of deep-sky objects and at the high power end for viewing the Moon and planets.
The 1.25” star diagonal included with the Inspire 100AZ is also mostly plastic, and the design is an Amici erecting prism, which provides correct images both left-right and up-down. Unless you plan on frequently reading signs and snooping on people’s reading material from a distance, this feature is essentially worthless and comes at a cost, too. Due to the way it works, any Amici erecting prism produces annoying bright spikes, glare, and additional chromatic aberration on bright targets – which doesn’t help when there are already glare issues with the dew shield and chromatic aberration from the objective lens itself to begin with.
The finder included with the Inspire 100AZ is Celestron’s “StarPointer Pro” red dot finder. Advertised as an improvement over Celestron’s standard “StarPointer” (itself a generic red dot finder like the kind sold with many beginner telescopes), the StarPointer Pro is basically a failed attempt to copy the Telrad. It has two circles instead of a dot in the middle, both of which are exceedingly wide. It is somewhat hard to actually centre anything in the finder, or align it precisely, or keep it aligned with the telescope particularly well. However, for a telescope with a fairly short focal length and a consequently wide field of view, like the Inspire 100AZ, it works well enough to get targets in the field of view most of the time. But if you’re hunting for faint fuzzies that you might not recognise at first glance, we might recommend replacing the StarPointer.
There’s also a small red flashlight included with the Inspire telescopes, which mounts to the centre of the hub of the tripod below the mount head and can be detached from the mount with the turn of a knob. It’s a little too bright to use as a plain flashlight at night, but the diffuser built into the tripod makes it into a really great tray light to softly illuminate your accessories without completely ruining your night vision.
Lastly, and most controversially, is the lens cap/smartphone adapter. Celestron’s design here is straight up bizarre. By removing a small plug from the cap and removing the eyecup from your desired eyepiece, then camping the assembly together with a small plastic screw, you can slide your smartphone between the elastic straps on the lens cap and use it as a crude smartphone “digiscoping” adapter. However, this has a few caveats. For one, it won’t fit any aftermarket eyepieces that don’t have a flush barrel and removable eyecup. Secondly, it obstructs a portion of your smartphone’s screen, which can make setting your phone camera’s focus and other features somewhat difficult. Last but not least, you are entrusting your smartphone’s safety to some cheap elastic straps and a singular nylon thumb screw. So keep that in mind.
Holding your phone up to the eyepiece with a steady hand is nearly as good an option as using the Inspire’s included phone adapter, and dedicated smartphone adapters are not that expensive to buy aftermarket and will be a safer and easier to use option for your phone.
The Inspire 100AZ’s mount is an alt-azimuth design that you aim up and down, and in this case, essentially a very beefed-up version of a camera tripod. The telescope sits outboard of the altitude axis on top of it. There are no fine adjustment or slow-motion control knobs, cables, or gears, and the only control adjustments of any kind are a lock for the azimuth axis and a lock/handle for the altitude axis. The tripod legs are tubular steel. The optical tube attaches to the Inspire mount with a standard Vixen-style dovetail plate and saddle, so you could theoretically put another telescope on the mount, but it isn’t really capable of holding much weight besides another small refractor.
Believe it or not, despite the lack of fine adjustments and obviously non-astronomical design intent, the Inspire mount design works pretty well. With a longer or heavier telescope, a mount like the Inspire design would probably tip over and struggle to stay put unless almost completely locked on the altitude axis (hence why the Inspire 100AZ uses so much plastic), but it works just fine in this case. Making fine adjustments at high magnification takes some finesse and getting used to, but it does work pretty well. Not perfect, not as good as a Dobsonian, but well enough.
Unlike the vast majority of tripod-mounted telescopes, which have some sort of accessory tray that requires an annoying process to secure to the legs, the Inspire 100AZ’s accessory tray is built into the tripod legs and just has to be locked into place when setting up the telescope. It’s also designed to actually hold accessories besides just eyepieces, and is big enough to fit a phone (which you can rest to use as a star chart with an app like SkySafari) – and the textured rubber on the tray should give you some peace of mind.
Should I buy a Used Celestron Inspire 100AZ?
A used Inspire 100AZ is a nice scope, though if poorly maintained, it’s very possible the scope could have irreparable damage thanks to its multitude of plastic components. Barring that, however, a used Inspire 100AZ will be fine if you can get it for a reasonable price-our recommendation is to never pay more than 80% of the new cost for a new telescope, eyepiece, or piece of astronomical gear.
The Inspire 100AZ is realistically the best refractor you’re going to get in its price range. The Inspire 100AZ is only an acceptable, but so-so telescope. We would recommend you consider a reflector instead, as few refractors of acceptable quality exist in this price range. All reflectors have larger apertures and, in some ways, better mounts and optics than the Inspire 100AZ. Here are some of our favorites.
- The Zhumell Z100 and Sky-Watcher Heritage 100P technically have slightly less light-gathering ability than the Inspire 100AZ, but don’t suffer from chromatic aberration and are much easier to aim. The shorter focal length and resultingly wider field of view helps, too.
- The Zhumell Z114 and Orion StarBlast 4.5 Astro beat the Inspire 100AZ in both light-gathering power and overall sharpness/clarity on smaller targets too. They’re
- The Sky-Watcher Heritage 130P provides a significant boost in light gathering and resolving power over the Inspire 100AZ at the same focal length, free of chromatic aberration and with a sturdy, easy-to-use tabletop Dobsonian mount.
- The Popular Science by Celestron StarSense Explorer DX 100AZ uses the same optical tube and includes the same accessories as the Inspire 100AZ, but with an improved alt-azimuth mount that has slow-motion adjustments – further aided by Celestron’s StarSense Explorer technology to make aiming the telescope even easier.
- The Sky-Watcher Heritage 150P provides double the light gathering ability of the Inspire 100AZ and 50% more resolution, all with no chromatic aberration or shaky tripod, and in a compact and portable package. The included accessories are well-made, and the tube collapses to make the telescope as easy to transport and store as possible. A computerized version, the Virtuoso GTi 150P, is also available.
- The Bresser Messier 6” f/8 Planetary Dobsonian has a 2” single-speed Crayford focuser, double the light gathering power, and 50% more resolving power than the Inspire 100AZ, mounted atop a full-sized and sturdy Dobsonian mount which requires neither a table nor tripod to be used. Other 6” f/8 Dobsonians are also available if you are unable to obtain an Bresser Messier 6”.
What can you see with the Celestron Inspire 100AZ?
A 100mm refractor has the capability to do a surprising amount of stuff. Thanks to the lack of reflective mirror surfaces or a central obstruction, the Inspire 100AZ performs similarly to a 114mm or so reflector. You won’t quite be able to resolve globular star clusters or see much in the way of detail in galaxies, even under dark skies, but the 100AZ can still show you the entirety of the Messier catalogue, and a wealth of detail on the Moon and planets.
With the Inspire 100AZ, you can make out Mercury’s phases (albeit with some difficulty) and Venus’s phases are easy to see. There’s a tonne of detail on the Moon, with craters and ridges as small as a few miles visible at high magnification on a steady night. Mars’ polar caps and a dark mark or two will be visible, as will be any dust storms that occur on the planet. Jupiter’s moons are just barely able to be resolved as tiny dots, with inky black shadows following them when they transit the planet. Jupiter itself will display a few cloud bands, some smaller storms if any are present, and, of course, the Great Red Spot, though it is becoming less and less great as it shrinks and its colour ranges from white to pink.
Saturn’s rings are easy to spot with the Inspire 100AZ, as is the Cassini Division within them and a few cloud bands on the planet itself, though they are not particularly colourful and appear as purely symmetrical strips. A few of Saturn’s moons can also be seen, with Titan being the brightest among them. Rhea, Tethys, and Dione are easy to spot; Enceladus and Iapetus are tougher.
Uranus and Neptune are unfortunately rather unexciting with the Inspire 100AZ-they’re difficult to distinguish from stars, their disks are so small that they are barely resolvable, and their moons are simply dim enough to be well out of reach of a telescope with only 100mm of aperture.
Outside the solar system, what you can see with the Inspire 100AZ broadly depends on your sky conditions. Under a light-polluted sky, you are basically limited to seeing the cores of the brightest galaxies, open star clusters, and some of the brightest nebulae. With good skies, however, you can see a lot more. Keep in mind that we’re not asking for perfection-what we’re talking about is being able to at least somewhat make out the Milky Way. Under skies like these, open star clusters explode into colourful gobs of stars straddled by dark dust lanes. Nebulae like Orion look spectacular, and with a good filter, you can view the supernova remnant in Cygnus known as the Veil, which stretches across an area of sky 10 times the width of the full Moon. Globular star clusters might look vaguely grainy, but they are beyond the resolving power of a 100mm telescope—albeit barely.
The Andromeda Galaxy’s elongated appearance and a dust lane or two are obvious with the Inspire 100AZ under dark skies, as are its two companion galaxies, M32 and M110. M33, the Triangulum Galaxy, has somewhat-visible spiral arms, as does M81. M82’s dust lanes are obvious. You may even be able to vaguely tell that M51 and M101 are spirals, though it’ll be tough. And galaxy groups like the Virgo Cluster and Leo Triplet are visible, as well, although rather dim and devoid of detail.