The Orion SkyQuest XT4.5 Classic is a 114mm (4.5-inch) Newtonian reflector on a manual Dobsonian mount. With a 900mm focal length and f/7.9 focal ratio, it combines a relatively compact physical size with an optical system suited to straightforward visual observing of the Moon, planets and brighter deep-sky objects.
The telescope requires no electrical power, computerized alignment or motorized tracking. Objects are located using the finder and the optical tube is moved manually in altitude and azimuth, following the simple operating principle that defines a traditional Dobsonian telescope.
Although the XT4.5 shares its 114mm aperture with Orion’s StarBlast 4.5, the two telescopes have quite different characteristics. The XT4.5’s 900mm focal length is twice as long, making higher magnifications easier to achieve and producing a considerably slower f/7.9 optical system.
114mm f/7.9 Reflector Optics
The SkyQuest XT4.5 uses a 114mm primary mirror with a 900mm focal length, giving it a focal ratio of f/7.9. Its Newtonian optical design uses a secondary mirror near the front of the tube to direct light into the eyepiece.
The relatively long focal ratio makes the telescope well suited to lunar and planetary observing while still providing enough aperture for brighter objects beyond the Solar System. Compared with very fast Newtonian reflectors, the f/7.9 system is also less demanding of eyepieces and shows less obvious coma toward the edge of the field.
Like other Newtonian reflectors, the XT4.5 requires occasional collimation to keep its primary and secondary mirrors correctly aligned. Orion provided a center mark on the primary mirror to assist with this process.
Simple Manual Dobsonian Mount
The XT4.5 uses a manual Dobsonian altitude-azimuth mount. The optical tube moves up and down in altitude and rotates from side to side in azimuth, allowing the observer to point it across the sky without motors or complicated controls.
Once an object is centered in the eyepiece, the telescope is periodically nudged by hand to compensate for Earth’s rotation. Orion’s original instructions specifically describe following targets in this way as they drift across the field of view.
The relatively low eyepiece position means many adults will find the telescope most comfortable to use while sitting on a chair or observing stool, something Orion also recommended in its instructions.
What Can You See Through the SkyQuest XT4.5?
The Moon is one of the XT4.5’s strongest targets. Its craters, mountain ranges, maria and shadows along the terminator can be observed in considerable detail, with higher magnifications revealing progressively smaller features when atmospheric conditions allow.
The bright planets are also accessible. Jupiter’s four Galilean moons and principal cloud belts can be observed, while Saturn’s rings are clearly distinguishable from the planet. Venus displays its phases, and Mars can reveal some surface detail when it is favorably positioned.
Beyond the Solar System, the 114mm aperture can show open star clusters, double stars, brighter nebulae and some galaxies and globular clusters. Dark skies become increasingly important for these fainter targets, which will generally appear much subtler through the eyepiece than in astronomical photographs.
The 900mm focal length means the XT4.5 does not provide the exceptionally wide fields available from the shorter StarBlast 4.5, but it offers a useful balance between planetary magnification and general visual observing.
Portability and Setup
The XT4.5 was designed as a relatively compact Dobsonian. Its optical tube and base can be moved without the tripod, counterweights or separate mount components required by many other telescope designs.
Initial assembly is required, particularly for the Dobsonian base, although Orion supplied the optical components already installed in the tube. Once assembled, normal observing setup is straightforward: position the telescope on a reasonably level surface, insert an eyepiece, align the finder if necessary and begin locating targets.
Its compact dimensions make the XT4.5 considerably easier to store and transport than larger Dobsonians, although its long optical tube makes it less compact than a tabletop reflector such as the StarBlast 4.5.
Limitations to Consider
The XT4.5’s 114mm aperture provides useful observing capability but cannot match the light-gathering performance of larger 150mm, 200mm or greater Dobsonian telescopes. Fainter galaxies and nebulae therefore become more challenging, particularly from light-polluted locations.
The telescope is entirely manual, with no computerized object finding or motorized tracking. Observers must learn to locate targets themselves and periodically move the telescope to keep them in view.
Its 900mm focal length also means it cannot provide the same expansive wide-field views as short-focal-length reflectors and refractors. Conversely, this slower optical configuration is part of what makes the XT4.5 relatively straightforward for lunar and planetary observing.
Finally, the SkyQuest XT4.5 is a discontinued Orion telescope, so examples encountered today may vary in age, supplied accessories and condition.
Who Is the SkyQuest XT4.5 Best For?
The SkyQuest XT4.5 is best suited to observers who want a simple, compact manual telescope for the Moon, planets and brighter deep-sky objects without computerized setup or electrical power. Its 900mm focal length makes it particularly comfortable for general lunar and planetary observing, while its 114mm aperture still provides enough light-gathering ability to begin exploring star clusters, nebulae and other brighter deep-sky targets.
Specifications
- Optical Design: Newtonian reflector
- Aperture: 114mm (4.5 inches)
- Focal Length: 900mm
- Focal Ratio: f/7.9
- Mount: Manual Dobsonian altitude-azimuth
- Focuser: 1.25-inch rack-and-pinion
- Optical Tube Material: Steel
- Tracking: Manual