Celestron NexStar 127 SLT telescope: Full review

If you’re looking for an affordable telescope to view the solar system and bright deep-sky targets, then the NexStar 127 SLT is a great option. At a moderate price and with a decent-sized aperture of 5 inches, this Maksutov-Cassegrain is a worthy contender for those looking to upgrade on their basic telescope.

The Celestron NexStar 127 SLT comes with everything the amateur astronomer needs for a seamless night of observing, with the exception of AA batteries for powering the GoTo's motors. In the box, you'll find two 1.25 inch Plössl eyepieces (9mm and 25mm), accessory tray, red dot finder, software and instruction manuals along with the telescope tube, tripod and mount. The eyepiece holder also features an adapter that supports accessories that are 2 inches in diameter.

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NexStar 127 SLT: Design

• High-quality optical tube assembly 
• Setting up is intuitive
• Offers SkyAlign technology 
• Portable design for backyard observing and travel
• Computerized mount drains batteries quickly

The  Celestron NexStar 127 SLT tube is made of high-quality aluminum build with no sign of flimsy plastic features. Setting it up is extremely intuitive, with the optical tube assembly (OTA) slotting into place on the mount via a metal CG-5 Dovetail bar and secured by tightening a nut by hand. The stainless steel tripod is affixed to the mount using a large, plastic nut that screws upwards — there can be a touch of slack between the mount and tripod with this design, causing a wobble, so we recommend attaching the OTA last to ensure that the mount and tripod are threaded properly.  

The NexStar 127 SLT's mount includes a spirit level and it’s important to make use of this to ensure the telescope is stable during observations and ensures the GoTo system is able to achieve optimum performance. Even when fully set up the 127 SLT is quite portable, weighing in at 18 lbs (8.2 kg), making it ideal for astronomers who like to switch between observing in their garden and traveling to dark-sky sites. 

If this is your first time using a computerized scope and you’re concerned about setting it up then don't be — the procedure in getting the GoTo feature up and running is straightforward. The 127 SLT is fully-functional in a matter of minutes. 

Celestron provides a step-by-step guide along with software to assist with alignment but we do recommend you get to grips with the SkyAlign technology before heading outside for an evening, as reading instructions in the dark — even if you're making use of a red torch —may prove to be a challenge.

For effective alignment, we chose three bright stars that were sufficiently separated in the night sky. The telescope's computerized system responded well to our selection, taking away the fiddliness that comes with calibrating your instrument. For best SkyAlign results, astronomers should use the handset to enter the time (to the second) into the GoTo's computer, along with the longitude and latitude at their location.

On the whole, the telescope's GoTo system responded very well during our review and slewed to targets effortlessly, placing them close to the center of the field of view. The NexStar SLT's ability to track objects is also a pleasing feature.

Unfortunately, the Celestron NexStar 127 SLT does have a few downsides. The design is quite "top-heavy" and, while the telescope isn't on the brink of falling over, we do recommend investing in a tripod that’s able to hold the mount and tube much more steadily. 

The tripod also vibrates while the GoTo’s motors are in motion. As a result, we needed to stop and start focusing for steady observations since the target bounced around the field of view while using the eyepiece and simultaneously bringing our target into focus. The telescope's mechanism is also covered in a substantial amount of oil and grease that made smooth workings of the focuser a challenge.  

Another problem we discovered is that the computerized mount is quite demanding of the eight AA batteries that it requires. It’s a given that they won’t last for very long in cold conditions, but the batteries were drained in less than a couple of hours of observation. 

If you’re looking at using this form of powering the telescope, we strongly recommend investing in some good quality batteries. It's also wise to invest in a 12V DC power supply for powering the GoTo, something the NexStar 127 SLT isn’t supplied with — due to the reasonable price of this instrument though, this isn't a criticism.

NexStar 127 SLT: First light and functionality

• Additional spend required to reach useful magnifications 
• Optical system not capable of viewing all 4,000 objects in database
• Clear, crisp views of solar system targets, with good resolution of detail
• Mount allows a good level of astrophotography

During our review, we took advantage of a waning gibbous moon using the supplied 9 mm and 25 mm Plössl eyepieces, which provide magnifications of 167x and 60x. The NexStar 127 SLT has useful magnifications of 18x (minimum) and 300x (maximum), so you should expect to pay an additional $150 (£120) or more in accessories to get the very best out of the optical system.

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Observing the lunar surface was breathtaking through the field of view, with craters, rilles and lunar mare resolved to high clarity.

We ran our field of view along the moon’s terminator, taking in excellent sights of the rugged surface where lunar day meets lunar night. The craters Catharina, Aristoteles and Cyrillus were particularly stunning, with the 60x magnification picking out the shadows that fell beautifully across them, truly making them pop. Slewing over to the brighter craters Tycho, Longomontanus and Clavius using the handset, the 127 SLT’s optical system once again produced beautiful, clear and crisp results.

The telescope’s database contains around 4,000 objects. Sadly though, a good proportion of these are faint deep-sky objects that the 127 SLT’s optical system just isn’t capable of viewing due to its long focal length and small aperture. 

You will be able to just make a smudge of light out when observing galaxies, but this telescope is best used for solar system objects and the brighter deep-sky targets. We were able to resolve Jupiter’s cloud bands with ease given the steady seeing conditions and cleanly separate several pairs of double stars. The Orion Nebula (Messier 42) and the Pleiades star cluster (Messier 45) provided "wow!" moments using the supplied eyepieces, but even better views were had using Celestron's range of X-Cel LX eyepieces — the latter offered better eye relief and contrast.

Views are clear across an excellent proportion of the field of view and as expected with catadioptric telescopes — any color fringing is nowhere to be seen, with the NexStar 127 SLT being of no exception. 

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NexStar 127 SLT: Verdict

We are delighted with the performance of the NexStar 127 SLT. If you’re an observer, who is mainly interested in planetary or lunar views with an occasional dabble in deep-sky observations, then this telescope is an affordable instrument with stunning optics. The computerized mount is easy to set up and operate while attaching the components (mount, telescope tube, etc) is extremely intuitive. 

For a moderate budget, a great deal is supplied by Celestron but we do recommend investing in a range of eyepieces to make the most of the NexStar 127 SLT's optical system. It's also worth remembering that the computerized mount eats through batteries, so a more substantial power source is required. 

Using the focuser requires a little bit of skill. Our test unit's mechanism was covered in a lubricant that made using this feature difficult when it came to bringing an object into focus — trial and error achieved decent results. 

Since the telescope makes use of an alt-azimuth single arm mount, the Celestron NexStar 127 SLT is capable of moderate astrophotography. We were able to get fair images using a DSLR camera and short exposures — something that individuals who see themselves as at a beginner-to-intermediate level will no doubt be pleased with.