The Optical Tube
The Celestron Astro Fi 102 is a 4” (102mm) f/13 Maksutov-Cassegrain telescope with a focal length of 1325mm. Maksutov-Cassegrains are known for having sharp optics, and the Astro Fi 102 lives up to that promise. On a clear, steady night, you can see great views of the moon and planets all the way up to its theoretical limit of 200x magnification. At f/13, even the cheapest eyepieces will work fairly well, with little to no edge-of-field distortion at low powers. Maksutov-Cassegrain telescopes don’t really need to be collimated, but if they do, the Astro Fi 102 has adjustments for collimation behind the primary mirror.
Focusing the Astro Fi 102 is accomplished by turning a knob at the back of the telescope, which adjusts the spacing of the primary mirror with respect to the secondary mirror inside the telescope’s tube. This can result in minor “image shift” during focusing but is not a huge problem. The back of the Astro Fi 102 has proprietary threads with a 1.25” visual back provided to hold a 1.25” star diagonal; the visual back also has T-threads to directly screw on a DSLR camera with a suitable T-ring.
The Astro Fi 102 attaches directly to its mount with a Vixen-style dovetail bar, which allows it to be used with a variety of other astronomical mounts as well as attached to a photo tripod if you wish.
The Celestron Astro Fi 102mm Maksutov-Cassegrain comes with a 1.25” prism diagonal, which slots into the provided 1.25” visual back, and two 1.25” Kellner eyepieces: a 25mm for 53x magnification and a 10mm for 133x. These are both decent eyepieces with all-metal housings and glass lenses; they lack eyeguards, and the 10mm is a little short on eye relief, but the apparent field of view of around 50 degrees is sharp and not lacking in contrast.
For a finder, the Astro Fi 102 includes Celestron’s standard, generic “StarPointer” red dot finder, which is primarily used to line up the telescope with alignment stars during setup. It attaches with a standard interchangeable Synta/Vixen-style foot, so you could swap in a different finder if you wish, but there’s not much point in doing so.
The Astro Fi mount is an improved version of the older NexStar SLT and GT mounts and is similar to the Celestron SkyProdigy mount, which also has SLT design heritage. The mount is a simple GoTo alt-azimuth mount that can hold up to a 5-inch telescope. Compared to the SLT, it has better gears and a sturdier tripod, with extruded aluminum legs instead of the SLT’s too-small tubular steel legs. The accessory tray has plenty of room for eyepieces, flashlights, or your smartphone; one half has slots for the provided 1.25” Kellner eyepieces, and the other is covered in grippy stuff and has a well to put your smartphone in. This is much better than the annoying and largely useless eyepiece holders that often come with beginner telescopes as an accessory tray.
The Astro Fi mount is completely unsuitable for deep-sky astrophotography, of course (as is a 102mm f/13 Maksutov optical tube), but it works quite well for visual astronomy. You power the mount with a set of standard batteries and the external plug-in battery pack, or you can plug in another external power source. We would recommend that you get a rechargeable power supply as soon as you can to save money and for better reliability.
Setting up the Astro Fi mount is quite simple. After turning on the telescope and leveling the tripod, you connect to its WiFi network and open either Celestron’s SkyPortal app or SkySafari Pro on your smartphone/tablet. The app will guide you through centering and confirming a few alignment stars. Afterwards, you’re free to slew the telescope around the sky with push-button controls on your screen or select from a huge database of objects that the telescope will automatically point at and track for you. There are some unseen bonuses here besides the easy interface of a screen versus an old-fashioned keypad. The telescope can get precise location and time information from your device rather than relying on expensive internal GPS and clock units or you entering that information yourself. If you walk away and your device disconnects from the Astro Fi’s WiFi network, the telescope will keep tracking and remember its alignment information once you reconnect.
Should I buy a Used Celestron Astro Fi 102?
A used Astro Fi 102 should be fine, but older units tended to suffer from reliability issues with the WiFi network maintaining a connection to a device, which could be a problem. If you’re buying one that wasn’t purchased recently and the owner didn’t use it successfully, that could be a red flag. Price is also a concern; as with any electronic device or telescope, don’t pay too close to the new price for a used unit, especially since it will probably be without a warranty or any guarantees as to condition or the ability to get a refund.
Maksutov-Cassegrain telescopes are pretty hard to damage, but as usual, check to make sure that the optics are not damaged and are free of corrosion or fungus.
The price of the Celestron Astro Fi 102 is about the same as that of many 5″ and 6″ manual and GoTo telescopes. For a little more, you could also get an 8” or 10” Dobsonian. Any of these options will be much better for viewing than the small aperture of the Astro Fi 102.
- The Sky-Watcher Virtuoso GTi 150P has fully motorized GoTo and tracking controlled via your smartphone or tablet, in addition to significantly larger aperture and a much wider field of view than the Astro Fi 102. It can also be aimed manually with no ill effect to the GoTo alignment and compacts into an extremely small package thanks to its collapsible tube. A 130mm model is also available.
- The Sky-Watcher Heritage 150P is identical to the Virtuoso GTi 150P apart from lacking electronics, and is offered at an even lower price. Like the GTi 150P, the Heritage 150P has a 130mm equivalent model, the Heritage 130P, offered for an even lower price though slightly less capable.
- The Sky-Watcher Virtuoso 90 Catadioptric is a little smaller than the Astro Fi 102 and doesn’t have full GoTo, but has similar high-performance Maksutov-Cassegrain optics, motorized tracking, and an alt-azimuth mount that can be used either on its own on a tabletop or attached to a photo tripod. A solar filter is also provided in addition to the usual accessories.
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 offers double the aperture – thus twice the resolution and 4x the light gathering ability – of the Astro Fi 102 along with a pile of useful accessories and features mounted atop a sturdy and simple Dobsonian mount.
- The Explore Scientific 10″ Hybrid Dobsonian offers even more aperture than the AD8 and is almost as portable as the Astro Fi 102 and tabletop Dobsonians thanks to its truss tube design. However, the provided accessories are a bit lackluster.
- The Orion SkyQuest XT6 Classic Dobsonian is significantly more capable than the Astro Fi 102 and can handle 2” eyepieces, as well as not requiring a table or tripod for use. However, it’s nearly as expensive as an 8” or 10” scope and priced more than the equal-sized, fully GoTo Virtuoso GTi 150P.
- The Celestron Astro Fi 130 uses the same mount and includes the same accessories as the Astro Fi 102, but the 130mm f/5 Newtonian optical tube has quite a bit more light gathering and resolving power and offers a drastically wider achievable field of view more suited for viewing deep-sky objects than the 102mm Maksutov.
Aftermarket Accessory Recommendations
The Celestron Astro Fi 102’s included star diagonal and eyepieces are just fine, but you may want a few more oculars for additional magnification. A 32mm Plossl eyepiece will provide 41x magnification and a slightly wider true field of view than the Astro Fi’s stock 25mm Kellner eyepiece. A 15mm SWA or redline eyepiece will produce 88x magnification with the Astro Fi 102, bridging the gap between the stock 25mm and 10mm oculars.
A dew shield for the Astro Fi 102 is also a must. It will prevent condensation from forming on your telescope’s front corrector plate and also act as a lens hood, lessening glare from nearby light sources such as street lamps or the Moon.
What can you see with Celestron Astro Fi 102?
The Astro Fi 102’s long focal length, small aperture, and 1.25”-only eyepiece capabilities make it severely limited when it comes to viewing deep-sky objects. The Astro Fi 102 lacks the ability to fit huge open clusters or the largest nebulae in the field of view at all, and is too small to resolve globular star clusters or most planetary nebulae as anything more than smudges. You can see galaxies like Andromeda and the many galaxies making up the Virgo Cluster from decent skies, but don’t expect much; a few galaxies like M82 may show traces of detail like dust lanes, however. The brightest nebulae like the Orion Nebula (M42) still dazzle, and many open clusters do still fit in the field of view, such as M35, but a larger telescope shows them better.
The Astro Fi 102 does pretty well on the Moon and planets, however. Expect to have no trouble seeing the phases of Mercury and Venus, along with the ice caps on Mars. Mars shows some dark markings with the Astro Fi 102 on a steady night when it is at its closest to Earth. The Moon delights with thousands of details like craters, ridges, and mountains. Jupiter’s cloud belts and Great Red Spot can also be seen; the disks of the four large Galilean moons, along with their shadows, can be resolved by the Astro Fi 102 when they transit in front of the planet. Saturn’s rings and the Cassini Division within them can also be glimpsed, along with cloud belts on Saturn and a few moons. Uranus is resolved as a fuzzy bluish-green ball; Neptune is hard to distinguish from a star; and the moons of both ice giants are too dim to see with only 4 inches of aperture. Pluto is also too dim to see with such a small instrument.