Sky-Watcher Skymax 127 Review: Partially Recommended OTA

The Skymax 127 is nominally a 127mm (5”) f/12 Maksutov-Cassegrain with a focal length of 1540mm. In actuality, the primary mirror in this telescope is undersized, and the true clear aperture is about 120mm (4.7”), making the telescope an f/12.5 system. The difference caused by this 7mm loss is minimal, though it does make the scope a pretty marginal upgrade over a 102mm (4”) Maksutov, and the performance ends up being similar to that of a 114mm (4.5”) Newtonian. The secondary mirror on the Skymax 127 is an aluminum-coated “spot” on the rear face of the front corrector lens. The central obstruction by the secondary mirror is 31% by diameter—bigger than most Newtonian reflectors of this size but much smaller than that of a 5” Schmidt-Cassegrain, which is nearly 40%, enough to actually reduce contrast and image brightness. The Skymax 127’s internal baffling is quite good, though you can improve it by inserting black velvet into the baffle behind the primary mirror. 

Focusing with the Skymax 127 is accomplished by turning a knob on the back to move the primary mirror along a rod back and forth up the tube. In larger telescopes, this can cause the image to “shift” and appear to wobble as you focus, but the Skymax 127’s primary mirror is so small and lightweight that this issue doesn’t usually occur. And since the secondary mirror on the Skymax 127 is fixed in place, as with all Maksutov-Cassegrains, there’s simply no need-or ability-to collimate it, but a set of screws on the back of the scope can be adjusted to align the rear cell of the telescope with the primary and secondary mirrors if you absolutely need to.

While a 2” visual back and a 2” star diagonal are provided with the Skymax 127, this telescope absolutely cannot support the use of 2” eyepieces. For one thing, a 2” eyepiece, which often weighs more than a pound, is outlandishly heavy compared to the telescope itself (which weighs only about 8 lbs), and can cause balance or even stability problems if the Skymax 127 is used on a lightweight mount. But more importantly, the Skymax 127’s small baffle tube-and undersized primary mirror-are simply unable to illuminate the field of anything with more than a ~25mm field stop, which is about the field stop of a typical 25-30mm 1.25” ocular. Any wide-angle, low-power 2” eyepiece is going to vignette, and anything with a field stop of under 25mm can generally fit into a 1.25” barrel (the included 28mm, 2” LET ocular is an odd exception, being essentially a 1.25” in a 2” barrel for no good reason). The practical limitation of a 25mm field stop means the Skymax 127 can’t achieve a field of view greater than around 0.9 degrees, or a little less than twice the width of the full Moon, which hovers between ~0.45-0.55 degrees across depending on its exact distance from the Earth. This is also about the same field of view that the larger Skymax 150 and 180 can deliver, as they have longer focal lengths but slightly more generous baffle tube diameters. 

Make no mistake – a long-focus scope isn’t a wide-field deep-sky instrument, to begin with, even if you could use 2” eyepieces with the Skymax 127. Maksutov-Cassegrains are planetary scopes – embrace it. The benefit of an f/12.5 focal ratio is that pretty much any eyepiece is going to provide a sharp image, even Plossls or Kellners. For “wide” fields at low power, you don’t need fancy well-corrected oculars; a cheap “SuperView” or “superwide” based on the Erfle design works great. Orthoscopics and good Plossls will provide fantastically sharp planetary views on a low budget. These eyepieces are also usually lightweight and compact – great for travel with; you won’t need a big padded eyepiece case to accompany the Skymax 127 (which itself fits in a backpack). 

Thanks to its thick corrector plate, the Skymax 127 does need a little more time to cool down to ambient temperatures when brought outside from a warm indoor environment, compared to a different scope of this size such as a Newtonian reflector. It may take up to half an hour at worst. You could wrap the optical tube in reflective insulation or buy an electric cooler to speed up the process, but both solutions are arguably overkill at this aperture. Cooldown time is really something that only plagues larger scopes to a significant degree.

The Skymax 127 has a standard Vixen-style dovetail plate attached to the bottom of the tube, with multiple ¼ 20 holes at various positions to attach to a standard tripod head if needed. Either option is suitable for mounting the Skymax 127.

Accessories

The Skymax 127, as with the rest of the Skymax line, is usually sold only as an optical tube, with the expectation that you will be shopping for stuff to go with it—though the 127mm model is also offered paired with the AZ-GTi mount, a 1.25” visual back, a 1.25” star diagonal, and a pair of 1.25” eyepieces, which serve it well. Thus, if you’re planning on buying this as a tube only, the included accessories are probably something you’ll replace anyway and are really just a bonus.

As with most commercial catadioptric telescopes, the Skymax 127 has a threaded rear cell to which you attach a visual back—though with a different thread from the common, universal accessories meant for Schmidt-Cassegrains; you’ll need an adapter to use those. As we previously noted, a 2” star diagonal is included. The 2” diagonal is basic, with no fancy features like a dielectric mirror coating or brass compression ring, but it works fine. However, since a 2” eyepiece can’t be properly utilized with the Skymax 127 anyway, replacing it with a 1.25” diagonal would be a good idea, especially since it’ll shave off quite a bit of weight and take up less space if you plan on keeping the scope in a case or bag.

For an eyepiece, the Skymax 127 is provided with a 28mm, 2” “LET” eyepiece—essentially a Kellner—with an apparent field of view of around 55 degrees. It provides 55x when used with the Skymax 127. The 28mm LET eyepiece works fine even with the baffle tube limitations of the Skymax 127, but it’s essentially an unusually bulky and unnecessarily 2”-barrelled basic eyepiece which doesn’t cost much and isn’t exceptional.

The finderscope included with the Skymax 127 is yet another basic, ultra-simple 6×30 magnifying finderscope with crosshairs and an upside-down view. The 30mm aperture of this finder should show you slightly fainter stars than what you can see with the naked eye, provided you’re able to comfortably look through it, and the field of view is around 7 degrees, about the same as that of a typical pair of 7x50mm binoculars, but dimmer and flipped over. The 6×30 finder works and doesn’t require any batteries to use, but if you’re okay with an occasional battery change, we’d probably recommend just replacing it with a cheap red dot finder. The view through the 6×30 is so dim that there really isn’t much of an advantage to its light-gathering power or magnification. 

Mount Recommendations

The Skymax 127 will work fine on anything that can hold 10 lbs or so of payload. This means a lightweight alt-azimuth mount such as a Vixen Porta, Explore Scientific Twilight I, or any of the various simple alt-azimuth mount heads which screw onto photo tripods will work fine. High-end photo tripods will also work, provided you are able to aim them smoothly well above the horizon. The Sky-Watcher HEQ5 is also a good choice.

Sky-Watcher offers the Skymax 127 with a set of 1.25” accessories mounted atop the lightweight, portable AZ-GTi mount, which is a mount/scope combination we’d recommend.

Should I buy a Used Sky-Watcher Skymax 127?

There’s little to go wrong with a used Maksutov-Cassegrain with the Skymax 127, besides checking that the mirror coatings are in good shape. The focuser should move smoothly; an older scope may need the focuser lubricated, but doing so isn’t too difficult. 

Aftermarket Accessory Recommendations

A dew shield for the Skymax 127 will help prevent condensation from forming on the scope as well as keep some stray light out of the tube, helping to improve contrast. You can make one yourself or purchase one.

Picking out a set of eyepieces for the Skymax 127 depends on your budget and requirements, but at the minimum, a 10-12mm and a 6-8mm eyepiece would be good ideas, and if you’re switching to a 1.25” star diagonal, a good 25-32mm Plossl or wide-angle eyepiece is a good choice for low power. Our top picks would be a 32mm SVBONY Plossl (47x), a 12mm Agena Starguider (125x), and a SVBONY 2x Barlow lens to double these eyepieces’ respective magnifications to 94x and 250x.

Planetary imaging with the Skymax 127 and a high-speed video CMOS camera such as the ZWO ASI120MC-S or ZWO 224MC, combined with a 2x Barlow lens to increase image scale by bringing the scope up to f/25 and a 3000mm focal length, is possible. The caveat is that we’d recommend a nicer Barlow lens or focal extender like the offerings from Explore Scientific or Tele-Vue for the best possible image quality. However, the Skymax 127 is on the small side when it comes to resolving power and image brightness for the job, so we’d recommend a bigger telescope for the task, such as the Skymax 150 or 180, or one of Celestron’s larger Schmidt-Cassegrains.

What can you see with Skymax 127?

The Skymax 127 is primarily a lunar, planetary, and double star instrument. You can, of course, see the phases of Mercury and Venus, and Mars will at least show its polar ice cap. When Mars is at opposition and close to Earth, you should be able to see a number of dark markings on the planet’s surface when atmospheric conditions permit. The Moon shows features just a few miles wide, with a variety of different regions showing high contrast depending on the Moon’s exact phase. You should be able to resolve dozens of small craterlets in the large crater of Clavius.

The Skymax 127 reveals all four of Jupiter’s moons easily, and they should be able to be resolved as tiny disks, though this becomes an easier task when they transit in front of Jupiter. Jupiter’s cloud belts display a variety of different colors, from gray to blue, red, tan, brown, and even pink. The Great Red Spot can be resolved at high magnification, provided it’s on the side of Jupiter facing Earth when you look for it, and it can be somewhat difficult to distinguish from the surrounding South Equatorial Belt, which often has a similar if not identical color.

Saturn’s rings look fantastic with the Skymax 127, and during good seeing, you should have no trouble resolving the Cassini Division in the rings too. Saturn has a few cloud belts of slightly different colors, which should also be visible. A half dozen moons, all appearing as dim star-like points, are visible around Saturn, provided you don’t have too much light pollution. Uranus and Neptune are small, bluish dots, neither much more than a fuzzy “star” in appearance. Neptune’s moon Triton is extremely difficult to observe in a telescope of this small aperture, though it can be done. Forget about Pluto.

The Skymax 127 is a little lackluster on deep-sky objects. You don’t have enough resolving power or light-gathering ability to resolve globular clusters or details in most galaxies, and the narrow field of view is limiting when it comes to larger and brighter targets such as open star clusters and nebulae. That’s not to say there’s nothing to see, but there are certainly much better telescopes for deep-sky viewing of the same aperture or price. You can still see dust lanes in a few of the brightest galaxies like Andromeda (M31) or look at groups like the Leo Triplet and Virgo Cluster, but don’t expect much, especially if you live under light-polluted skies where it will become even more difficult to see anything at all. The Skymax 127 does, however, shine on double stars, resolving them right to the theoretical limit. Unlike a Newtonian reflector, there are no diffraction spikes. The smaller central obstruction than a Schmidt-Cassegrain and greater quality control of the optics make for sharper, pinpoint stars, and you need not worry about the chromatic aberration which most refractors of this size – at least the affordable ones – are likely to have.