The Optical Tube
The Astro Fi 127 shares identical specifications with other “127mm” Maksutovs offered by Celestron, Sky-Watcher, and several other brands. However, it differs slightly from the 127mm models provided by Bresser, Explore Scientific, and Meade, which feature a marginally different optical design and a true 127mm aperture. In practice, the primary mirror of the SkyMax 127 Maksutov is slightly undersized, stopping it at about 120mm in aperture. This minimal reduction makes the scope half an f-stop slower at f/12.5. Like other Maksutovs sold under the Celestron banner, the Astro Fi 127 comes with a 1.25″ visual back that has a different thread system than Schmidt-Cassegrain accessories use. The included 1.25″ visual back also features built-in T-threads for attaching a DSLR camera. An aftermarket adapter can be purchased for using Schmidt-Cassegrain visual backs, adapters, or a 2″ diagonal. However, a 2″ diagonal will vignette significantly and usually isn’t worth the effort for the marginal useful field of view gained from using 2″ oculars with this scope. An f/6.3 reducer meant for Schmidt-Cassegrains will vignette severely and should not be used with the Astro Fi 127.
The focusing mechanism on the Astro Fi 127 operates through the rotation of a knob situated on the rear of the scope. This action results in the primary mirror moving back and forth along a rod within the tube. In the context of larger telescopes, this method could potentially cause image “shifting” and an impression of wobble during the process of focusing. However, the diminutive size and light weight of the Skymax 127’s primary mirror make such issues uncommon. As is typical of all Maksutov-Cassegrains, the secondary mirror on the Astro Fi 127 is fixed, negating the need or ability for collimation. Yet, should the need arise, the alignment of the rear cell with the primary and secondary mirrors can be adjusted through a series of screws on the back of the scope.
It’s essential to bear in mind that a long-focus telescope like the Astro Fi 127 is not naturally suited to wide-field deep-sky observation, even if 2″ eyepieces could be practically utilised. Maksutov-Cassegrains are primarily engineered with planetary observation in mind. The key advantage of an f/12.5 focal ratio is its versatility; it facilitates sharp imaging with almost any eyepiece, including Plossls or Kellners. For “wide” fields at lower power, there’s no requirement for complex, well-corrected oculars; an affordable “SuperView” or “superwide” based on the Erfle design is quite sufficient. Orthoscopics and high-quality Plossls provide exceptionally sharp planetary views on a relatively modest budget.
One critical consideration with the Astro Fi 127 is its cooldown time. Due to its thick corrector plate, it requires a longer period to reach ambient temperatures when transferred from a warm interior environment to the outdoors, compared to other scopes of equivalent size, such as a Newtonian reflector. In more extreme cases, this process could take up to half an hour. While it might be tempting to consider wrapping the optical tube in reflective insulation or investing in an electric cooler to hasten the process, such measures are likely excessive for this aperture size. Cooldown time becomes a more significant factor when dealing with larger scopes.
The Celestron Astro Fi 127 Mak comes supplied with two eyepieces: a 25mm Kellner, which provides low power at approximately 60x magnification, and a 10mm Kellner, which offers a medium-high power of around 150x. While these eyepieces perform satisfactorily, at this price point, one might reasonably expect Plossls, which would likely provide a slightly enhanced viewing experience.
Accompanying the Astro Fi 127 is a prism star diagonal, which is pleasingly high-quality. This is in stark contrast to the cheap, poorly constructed mirror diagonals typically included with entry-level scopes, which tend to produce images that are dim and lacking in sharpness.
In terms of its finderscope, the Astro Fi 127 is equipped with a standard “StarPointer” red dot LED device – a mainstay of most beginner scopes in the current market. It is well-constructed and more than adequate for the task of aligning the Astro Fi 127’s GoTo system. Once the alignment process is complete, it’s unlikely you’ll find a need for it again during your observing session.
The Celestron Astro Fi Mount
The Astro Fi mount represents an enhanced version of the older NexStar SLT and GT mounts, sharing similarities with the Celestron SkyProdigy mount, which also draws from SLT design heritage. This mount is a straightforward GoTo alt-azimuth mount, capable of supporting a telescope up to 5 inches in size. Compared to the SLT, it boasts improved gears and a more robust tripod, featuring extruded aluminium legs as opposed to the SLT’s inadequately small tubular steel legs. The accessory tray provides ample space for eyepieces, flashlights, or your smartphone. One half of the tray has slots for the supplied 1.25” Kellner eyepieces, while the other half features a grippy surface with a well-designed spot to secure your smartphone. This is a significant improvement over the often frustrating and largely ineffective eyepiece holders that frequently come with beginner telescopes as an accessory tray.
Of course, the Astro Fi mount is not suitable for deep-sky astrophotography (just as a 127mm f/12.5 Maksutov-Cassegrain optical tube isn’t), but it performs admirably for visual astronomy. The mount is powered either by a set of standard batteries and the external plug-in battery pack, or you can connect another external power source. It’s recommended to acquire a rechargeable power supply at your earliest convenience for cost-effectiveness and greater reliability.
The set-up process for the Astro Fi mount is refreshingly straightforward. After switching on the telescope and levelling the tripod, you connect to its WiFi network and launch either Celestron’s SkyPortal app or SkySafari Pro on your smartphone or tablet. The app guides you through the process of centring and confirming several alignment stars. After this,
Should I buy a Used Celestron Astro Fi 127?
Regarding second-hand Astro Fi 127 telescopes, they can be a good option. However, it’s worth noting that older models have been known to have some reliability issues with maintaining a WiFi connection to a device, which could prove problematic. If the telescope you’re considering wasn’t purchased recently and the previous owner struggled to use it successfully, this could be a potential warning sign. Cost is another significant consideration. As with any electronic device or telescope, it’s not advisable to pay a price near to the new price for a used model. This is particularly pertinent given that it’s likely to come without any warranty or guarantees regarding its condition, or any potential for a refund.
Maksutov-Cassegrain telescopes are generally robust and difficult to damage, but as always, it’s prudent to ensure the optics are free from damage, corrosion, or fungal growth.
Let’s explore some of the similarly priced alternatives to the Celestron Astro Fi 127 in more detail:
Under 800 Range
- The StellaLyra 10″ f/5 Dobsonian boasts offers twice the resolution and over four times the light-gathering capacity compared to the Astro Fi 127. This is due to its large 10″ primary mirror. It also comes with an array of accessories, such as a 2″ low-power, 30mm focal length wide-angle eyepiece, a 9×50 finder scope, and a 9mm high-power Plossl eyepiece.
- The Celestron StarSense Explorer 8″ Dobsonian provides some computerized pointing capabilities, albeit without motorized tracking, thanks to its StarSense Explorer technology. It has superior light gathering and resolving power compared to the Astro Fi 127 due to its 8″ aperture on a stable Dobsonian base. Although it’s relatively easy to set up, transport, and use, it comes with a limited range of accessories.
- The Sky-Watcher Virtuoso GTi 150P offers a 50% increase in light-gathering ability, enhanced optics, a wider field of view, and slightly better resolution compared to the Astro Fi 127. Its FreedomFind encoders allow for manual aiming, the mount is controlled over WiFi, and setup is incredibly easy. The 150P’s collapsible tube design makes it easy to transport, and its short focal length presents a wide field of view, making it an excellent choice for deep-sky observation. The Heritage 150P is a more cost-effective alternative, offering the same optical performance as the Virtuoso GTi 150P but without the electronic components.
- The Sky-Watcher Skymax 127 AZ-GTi uses the same optics and app-controlled mount design as the Astro Fi 127, but with a slightly superior pair of eyepieces, a more modular and easily dismantled mount, and best of all the AZ-GTi mount features FreedomFind encoders allowing you to aim the telescope around the sky manually to no ill effect, which is not the case with the Astro Fi mount of course.
Over 800 Range
- The Celestron StarSense Explorer 10″ Dobsonian boasts a huge 10” aperture, which allows for four times the light-gathering ability and double the resolution of the Astro Fi 127. It also incorporates Celestron’s StarSense Explorer technology, which assists users in manually navigating the night sky. Despite its large aperture, this Dobsonian telescope is relatively lightweight and easy to transport, thanks to cutouts in the base and handles on the tube. Although the provided accessories are minimal, the telescope offers excellent value in terms of aperture and portability for its price.
- The Sky-Watcher Skyliner 250P FlexTube GoTo Dobsonian also has double the resolution and four times the light-gathering power of the Astro Fi 127. It is equipped with full motorized tracking and GoTo capabilities, making it a highly user-friendly choice for beginners and experienced astronomers alike. Sky-Watcher’s unique FreedomFind encoder system allows users to manually aim the telescope without interfering with the alignment or motors in the mount.
- The Celestron NexStar 6SE offers greater stability than the Astro Fi mount, although its hand controller is slightly less user-friendly. It provides similarly sharp views of the Moon and planets as the Astro Fi 127, and thanks to its larger aperture, also offers superior deep-sky views. When equipped with a focal reducer and attached to an equatorial mount, it also has some deep-sky astrophotography capabilities.
- The Celestron NexStar Evolution 6 model shares many similarities with the NexStar 6SE, most notably the C6 XLT telescope optical tube. However, the Evolution 6 provides a variety of mechanical enhancements over the more affordable NexStar 6SE. Additionally, it includes a built-in Wi-Fi adapter and lithium battery, making setup and usage even more straightforward.
Aftermarket Accessory Recommendations
A dew shield is indeed a highly beneficial accessory you should purchase right away for your Astro Fi 127. It not only reduces the chance of dew forming on the front corrector plate but also mitigates glare at the eyepiece and improves overall contrast. Additionally, it offers protection against common hazards that can damage the front corrector’s sensitive optical coatings, such as fingerprints and pollen.
Extra eyepieces can further enhance your observing experience. For instance, a 32mm Plossl eyepiece yields a magnification of 47x, which is slightly lower than the provided 25mm eyepiece, thereby offering a broader field of view that is more suited for deep-sky objects. You might also consider replacing the telescope’s standard 10mm Kellner eyepiece with a 9mm redline or goldline eyepiece for a slight increase in power, sharper views, improved eye relief, and a wider field of view. For those steady nights, a 7mm planetary eyepiece can maximize the usable magnification to 214x. A 15mm redline or goldline eyepiece (100x) would slot nicely between the telescope’s included eyepieces in terms of magnification and focal length.
What can you see?
The Astro Fi 127, like all Maksutov-Cassegrain telescopes, is primarily engineered for observations of small and bright targets, such as the Moon, planets, and binary star systems. The phases of Mercury and Venus can be clearly observed, and Mars readily presents its polar ice cap. During periods when Mars is in opposition and at a close distance to Earth, the telescope can reveal several dark markings on the planet’s surface, provided the atmospheric conditions are favourable. The Moon is rendered in fine detail, with features as narrow as a few miles becoming visible. Depending on the Moon’s precise phase, various regions display high contrast. Within the expansive crater of Clavius, dozens of smaller craterlets can be discerned.
All four of Jupiter’s moons are easily observable through the Astro Fi 127, appearing as minuscule discs. This becomes particularly apparent when they transit in front of Jupiter. Jupiter’s cloud belts present a diverse colour palette, ranging from greys and blues to reds, tans, browns, and even pinks. The Great Red Spot can be resolved at high magnification, provided it is on the side of Jupiter facing Earth when you observe. However, distinguishing it from the adjacent South Equatorial Belt can pose a challenge due to their often similar, if not identical, colouration.
Saturn’s rings are spectacularly displayed through the Astro Fi 127, and in favourable seeing conditions, the Cassini Division within the rings should be easily resolved. Saturn’s various cloud belts, each exhibiting slightly different colours, should also be discernible. Under conditions of minimal light pollution, around half a dozen moons, appearing as faint star-like points, can be observed surrounding Saturn. Uranus and Neptune present as small, bluish specks, both resembling a fuzzy “star”. Neptune’s moon Triton is a formidable challenge to observe with a telescope of this modest aperture, although not an impossibility. Pluto, however, remains elusive.
Double star observations are another area where the Astro Fi 127 shines, resolving them to their theoretical limit courtesy of its sharp Maksutov-Cassegrain optical design. Unlike a Newtonian reflector, there are no diffraction spikes present. The smaller central obstruction, compared to a Schmidt-Cassegrain, coupled with superior quality control of the optics, results in sharper, more defined stars. Furthermore, you can disregard the chromatic aberration that most refractors of this size – especially the more affordable ones – tend to exhibit.
Regarding deep-sky objects, the Astro Fi 127’s performance is somewhat limited. It lacks the necessary resolving power or light-gathering capability to resolve anything but a few of the brightest globular star clusters, such as M3, M13, and M22. Similarly, observing detailed features in most galaxies with this telescope might be a tall order, especially for beginners. The Astro Fi 127’s naturally limited field of view constrains the observation of larger and brighter targets such as open star clusters and nebulae, meaning that there are arguably better-suited telescopes of a similar aperture or price range for deep-sky observation. You can still catch a glimpse of dust lanes in a few of the brightest galaxies, such as Andromeda (M31), or study groups like the Leo Triplet and Virgo Cluster. However, it’s wise to manage your expectations, particularly if you’re observing under light-polluted skies, where visibility becomes even more of a challenge.
The Celestron Astro Fi mount’s cheap design and manufacture, alt-azimuth format, and rather puny trip, combined with the Astro Fi 127’s remarkably slow f/12.5 focal ratio, make this telescope wholly unsuitable for deep-sky imaging. However, with the assistance of an inexpensive CMOS planetary video camera and a 2x Barlow lens, it is entirely possible to achieve satisfactory images of the Moon and planets using the Astro Fi 127.