The Optical Tube Performance Of Orion Skyquest XT 4.5
The Orion Skyquest XT4.5 Dobsonian is a 114mm f/7.9 Newtonian reflector, optically identical to the Celestron PowerSeeker 114 scopes and with a focal length of 900mm. However, the XT4.5’s tube boasts superior mounting and accessories to the PowerSeeker and other common 114/900 “hobby killer” scopes, which allow you to get the most enjoyment possible out of it.
In my experience, the XT4.5 is superior in various fronts to shorter tabletop telescopes like the Sky-Watcher Heritage 130/150, the Celestron StarSense Explorer tabletop Dobsonians, the Orion StarBlast, the AWB OneSky, and the Zhumell tabletop Dobsonians. It offers a higher collimation tolerance and slightly crisper images, thanks to its longer f/8 focal ratio. Additionally, viewers won’t notice any coma at the peripheries, which can be an issue with faster reflectors.
Speaking of collimation, the XT4.5’s primary mirror is easily adjusted for precise collimation without tools. A hex key is provided for adjusting the secondary mirror’s three screws. While it might be tempting to replace them with thumb screws, thumb screws are more likely to lose collimation. The XT4.5’s secondary mirror should never need adjustment after the first time you do it with the stock screws.
With a 900mm focal length, the XT4.5 makes it possible to attain high magnifications without resorting to extremely short focal length eyepieces or a Barlow lens. Focusing is less challenging as the depth of field is greater at a longer focal ratio. Especially for those keen on observing the Moon and planets, the XT4.5 undoubtedly provides a competitive advantage over f/4 and f/5 tabletop scopes, even the slightly larger 130mm f/5 units. Though past that point, the substantial increase in aperture makes up for any other deficiencies in high-power observing.
However, potential buyers should note the telescope’s 900mm focal length limits the maximum true field of view to about 1.8 degrees (with a 32mm or 40mm Plossl eyepiece). This is roughly half of what you’d get with a 4.5” f/4 scope like the Orion StarBlast Astro or Zhumell Z114. For those wishing to gaze at expansive star clusters or nebulae or those wanting greater ease in locating celestial objects, this is an essential factor to consider.
Being 35” long, the XT4.5’s optical tube will not fit in carry-on luggage or a backpack like shorter tabletop Dobsonians. If you plan on carrying the scope to your observing site on a regular basis and need it to fit in a bag or suitcase, a more compact telescope like the Orion StarBlast Astro 4.5 or Zhumell Z114 may be a better choice.
The focuser on the XT4.5 is a standard plastic 1.25” rack-and-pinion unit. You can’t really swap it out for a 2” focuser, and in any case, the telescope’s secondary mirror is not big enough to illuminate the field of a 2” eyepiece, so a 1.8° field is the absolute widest you can get.
Conveniently, the Orion SkyQuest XT4.5 features a grab knob at the front, acting as a lever to adjust the scope’s position. While some might find the knob a tad small, it’s likely to be a hit among younger users. Another user-friendly addition is the carrying handle attached to the tube, a feature many wish was standard across the larger Orion SkyQuest Dobsonian models.
About the Accessories
Out of the box, the SkyQuest XT4.5 includes two 1.25” Sirius Plossl eyepieces: a 25mm (36x) and a 10mm (90x). These eyepieces surpass many entry-level telescopes’ offerings in terms of quality. For greater magnification, a 6mm “goldline” or “redline” planetary eyepiece could be considered, but the provided 10mm Sirius is an excellent starter. Both of these eyepieces have a 52° apparent field of view. The 10mm is short on eye relief, as is common with 10mm Plossl and Kellner-type eyepieces; you may find it rather uncomfortable to use, and it is utterly impossible to look through if you have glasses on. However, these oculars are plenty sharp to get you started.
A collimation cap is also included with the XT4.5. Because this telescope has a long focal ratio and much less strict tolerances than a fast tabletop reflector, it is very easy to collimate.
While this telescope shines in many areas, the included 6×26 erect-image finderscope seems to be its Achilles heel. Although better than the basic 5×24 plastic variants often bundled with starter scopes, the Orion 6×26’s limited aperture restricts its usefulness. The erecting prism in the finderscope further dims the image, which is already dim. A red-dot finder, though not perfect, would be a more effective choice for this task.
You can buy the XT4.5 with a kit that also includes a 2x barlow, a cheap red flashlight, a moon map, a planisphere, and an observing guide. These are all mildly useful at best, and you would probably be better off buying a dedicated flashlight and a short-focal-length eyepiece separately.
Reviewing the XT4.5 Mount
The Orion SkyQuest XT4.5 Classic is equipped with a spring-tensioned Dobsonian base, echoing the robust and straightforward design of its larger counterparts in the XT Classic series. Originating from John Dobson’s innovative designs in the 1960s, the Dobsonian mount transformed amateur astronomy with its affordability and functionality. Unlike most tabletop telescopes with single-arm mounts, the XT4.5 benefits from a dual-bearing support with its altitude axis riding on proper Teflon pads. This is more stable and consistent in its movements than the simple bolt-and-washer setup of most tabletop Dobsonians.
This Dobsonian design is an alt-azimuth mount, permitting fluid vertical and horizontal movements, making aiming the telescope simple and easy, even at high magnifications, to make tracking adjustments. The use of Teflon pads in the mount ensures friction-based, smooth motion. The telescope’s weight distribution gives it a low center of gravity, which makes the setup very stable and lowers the risk of it falling over.
Notably, the design of the XT4.5 has its feet spread a tad wider than the upper portion of the base. While this might challenge placement on narrower platforms like milk crates, it’s a conscious design choice that enhances the telescope’s overall stability.
Should I buy a used Orion Skyquest XT4.5?
If the price reduction compared to buying new is fair, then go for it. Make sure that the mount is not damaged or missing any laminate.
Alternative Recommendations
The Orion SkyQuest XT4.5 isn’t our top recommendation within its price bracket, as it is significantly more expensive than other 4.5” reflectors, and you could get a 5-6” scope for the same amount of money. As such, you might want to explore these other Dobsonians, which may offer superior performance and/or come at a more appealing price tag.
Under $400
- The Sky-Watcher Heritage 150P, boasting a 6” aperture, provides a 33% enhancement in resolution and boasts over 80% more light-collecting prowess compared to the SkyQuest XT4.5. It also impresses with a collapsible tube for compact storage and, similar to the XT4.5, employs a single-armed tabletop Dobsonian mount.
- The Sky-Watcher Heritage 130P is, in essence, a scaled-down 150P, and it slightly surpasses the XT4.5 in light-collecting and resolving power. It too boasts a notably compact collapsible tube and a user-friendly tabletop Dobsonian mount.
- The Zhumell Z130 Tabletop Dobsonian has optics identical to the Heritage 130P, but with a closed tube design. The computerized Celestron StarSense Explorer 130mm Dobsonian is merely a rebranded Z130 upgraded with the StarSense Explorer object-locating technology.
- The Orion StarBlast 4.5 Astro and Zhumell Z114 share the 114mm aperture and Dobsonian mount of the XT4.5 but with half the focal length, allowing for a wider field of view and a more compact telescope, and at a lower price tag. The Celestron StarSense Explorer 114mm Dobsonian is identical to the StarBlast/Z114 but features Celestron’s StarSense Explorer technology to assist in finding deep-sky objects.
$400-$800
- The Apertura AD8/Zhumell Z8/Orion SkyLine 8 leaves the XT4.5 in the dust when it comes to light-collecting power, with a primary mirror delivering around 3x the surface area, transforming what were once elusive deep-sky objects into vivid and detailed spectacles. This powerhouse also offers nearly double the resolution of a 4.5” telescope. The cherry on top includes its dual-speed focuser, a variety of eyepieces, an integrated cooling fan, and adjustable bearings for optimal balance, all of which make it an incredible bargain for its price.
- The Sky-Watcher Virtuoso GTi 150P is a remarkable blend of manual and GoTo functionality. Think of it as a tech-savvy Heritage 150P: it comes with a tabletop Dobsonian mount and a collapsible tube for portability. Its crown jewel is the full computerized feature set, inclusive of motorized tracking and positioning steered by your smartphone. However, the FreedomFind encoders ensure that manual tweaks remain within arm’s reach.
- The Orion SkyQuest XT6 Dobsonian is a standalone 6” f/8 scope. Its f/8 focal ratio ensures ease of collimation and eliminates coma, like with the XT4.5, though as with the XT4.5 versus a tabletop, this comes at the cost of a somewhat restricted maximum field of view and a heftier tube compared to faster 6” f/5 reflectors.
- The Orion StarBlast 6 bears numerous similarities to the Sky-Watcher Heritage 150P, except it’s equipped with a full-length optical tube and a robust 2” rack-and-pinion focuser in place of the Heritage’s 1.25” helical unit.
- The Celestron Astro Fi 130mm stands out as a completely automated, tracking GoTo telescope, controlled via your smart devices. Its 5.1” aperture delivers respectable visuals, but at its price point, one could potentially opt for a larger Dobsonian with enhanced capabilities.
Aftermarket Accessory Recommendations
A 6mm “gold-line” or “red-line” eyepiece, offering 150x magnification, would be an ideal companion to augment your eyepiece collection for the Orion SkyQuest XT4.5, providing optimal high-power views for the Moon, planets, and double stars.
After you’ve equipped yourself with a high-power eyepiece, we would highly recommend you swap out the XT4.5’s included finder scope. As mentioned, the 6×26 finder scope included with the SkyQuest XT4.5 is far from ideal. For a replacement finder, we recommend a Rigel Quikfinder or an inexpensive red dot sight. The XT4.5’s diminutive size means you might have trouble balancing the telescope with a heavy Telrad or 50mm finderscope, as well as difficulty finding a place to situate the former on the XT4.5’s slender tube.
If you want to maximize the field of view with the XT4.5, a 32mm Plossl provides a 1.8° true field (the stock 25mm Sirius yields only 1.45°) for taking in the most expansive deep-sky objects, though this is still a fraction of what a wide-field 4.5” f/4 telescope like the Orion StarBlast or Zhumell Z114 can achieve.
To diversify the range of magnifications available to you, additional eyepieces within the 9–15mm range could be beneficial. For instance, a 9mm redline/goldline would provide 100x magnification, as well as greater eye relief and a wider/sharper view than the 10mm Sirius Plossl. A 15mm SWA or redline would offer around 60x, ideal for observing galaxies and smaller star clusters. However, the cumulative cost of these eyepieces might lead some to contemplate investing in a more substantial telescope or a high-quality nebula filter instead.
Another essential accessory to ponder over is the 1.25” Orion UltraBlock UHC nebula filter. Although no filter can combat light pollution directly, a good UHC filter significantly enhances contrast on nebulae by dimming objects that don’t emit the specific wavelengths associated with their ionized gases. As a result, these structures stand out more vividly against the night sky, unveiling their intricate details. Even under the pristine conditions of a dark sky, employing a UHC filter with the XT4.5 can accentuate the contrast, making these nebulae even more enchanting to observe.
What can you see?
The Orion SkyQuest XT4.5 Dobsonian offers a gateway to the mesmerizing universe that lies beyond our planet. Open clusters like M11 and M35 come alive in the eyepiece, with dozens of these star groupings easily within reach. Prominent emission nebulae like Orion (M42), the Lagoon (M8), and the Swan (M17) are easy to see even from light-polluted locales, though dark skies and/or a UHC filter offer the best views.
Galaxies are disappointing with any telescope under light-polluted skies, with their faint details easily obscured by the glow of city lights. Under such conditions, the XT4.5 will likely only reveal the brightest galaxies, and even then only as faint smudges devoid of any recognizable features. However, under the canopy of a pristine dark sky, the XT4.5 reveals some detail in the brightest galaxies to the patient observer. The dust lanes of Andromeda become evident, as do the spiral arms of M33. Enthusiasts can also glimpse features in other notable galaxies like M81, M82, and NGC 7331. The Virgo Cluster contains dozens of members, though even under a dark sky, they appear as little more than featureless smudges with a vague brightness at their centers.
The phases of Venus are a trivial job for any telescope to reveal, and under most conditions, the XT4.5 should show you those of much smaller Mercury as well. The Moon, of course, explodes with details; the SkyQuest XT4.5 resolves features as small as a few miles across when atmospheric conditions permit.
Mars, when it graces our skies during its close approach every two years, is a visual treat through the XT4.5. This scope’s optics under a steady sky will unveil the planet’s polar ice caps and intriguing dark markings, providing an intimate glimpse into our neighboring world. Jupiter, the giant of our solar system, offers a spectacular sight; the telescope captures its intricate cloud belts, the renowned Great Red Spot, and its four largest moons, also known as the Galilean moons.
Saturn, the jewel of our Solar System, offers an enchanting view through the XT4.5. Observers can marvel at its grand ring system, along with the subtle Cassini Division that lies within. Beyond the rings, the gas giant showcases its intricate cloud belts, its shadow contrasting against the rings, and an entourage of moons, including Titan, Rhea, Tethys, and Dione.
Venturing further out in our Solar System, Uranus and Neptune emerge as minuscule dots. Their appearance in a 114mm telescope like the XT4.5 is such that they could be mistaken for distant stars when viewed at low magnification. The faint moons of these ice giants remain hidden, even to the adept observer. Locating these distant planets might present a challenge for some, but with the right tools and knowledge, their identification becomes more straightforward. However, the dwarf planet Pluto remains elusive for the XT4.5, needing a significantly larger aperture and dark skies for it to be discernible.
