The Skymax 150 is a 150mm (6”) f/12 Maksutov-Cassegrain with a focal length of 1800mm. Maksutov-Cassegrains use all-spherical surfaces which are easy to manufacture to high standards of quality, so the performance of these scopes tends to be quite good; the bar is a bit higher than a typical 6” Schmidt-Cassegrain or Newtonian reflector. The secondary mirror on the Skymax 150, as with most Maksutovs, is an aluminized “spot” on the back of the corrector lens. The secondary mirror and baffle are not huge, obstructing only 31% by diameter, so contrast tends to be quite good, aided by an intricate system of baffling around the primary mirror and towards the back of the scope. You focus by turning a knob that moves the primary mirror back and forth along an internal threaded rod. The primary mirror in the Skymax 150 is not very big, and thus the dreaded “image shift” and “mirror flop”, which are often caused by the primary mirror wobbling during focusing, are minimal if not absent altogether in the Skymax 150.
Since the secondary mirror in the Skymax 150 is literally part of the front corrector lens, collimating the Skymax 150 is not something you should expect to do frequently, if ever. Small collimation screws on the back of the scope are used to adjust the rear cell of the telescope with respect to the primary mirror if needed.
The Skymax 150 is supplied with a 2” diagonal and a nominally 2” eyepiece, but the included eyepiece doesn’t actually have a field stop any wider than a 1.25” barrel, and the internal baffle of this telescope is too narrow for a 2” eyepiece. Attempting to use a wide-angle 2” eyepiece with a field stop of 30mm or more is going to cause vignetting. So in practice, you’re limited to a maximum field of view of around 0.9 degrees—for comparison, the full Moon is around 0.45-0.5 degrees, and a typical 6” SCT can support a 1.4-degree field; a 6” Newtonian can achieve a field of well over 2 degrees. A field of under 1 degree limits what you can fit with regards to deep-sky objects by quite a bit, and the 1800mm focal length means that “low” power is usually above 60x. This is nice for planetary viewing—something like a 6mm eyepiece is already at the magnification limit of the scope—but the Skymax 150 simply isn’t a deep-sky scope.
The long focal ratio of f/12 also means that even the simplest eyepieces, such as Plossls and Kellners, work great. For medium and low magnifications, cheap “SuperView” and similar Erfle designs are sharp right out to the edge of the field, so you can forego fancy premium oculars altogether—great for travel when you don’t want to worry about losing or damaging an expensive collection of eyepieces.
Optically, the biggest drawback of the Skymax 150 is its cooldown time. The Maksutov corrector is big and thick enough that it can take a while for warm air to escape the tube if the scope is taken outside on a cool night. Various solutions, such as blowers you insert into the back of the scope or wrapping the optical tube in reflective insulation, exist, but none are convenient and most are somewhat costly.
To attach to a mount, the Skymax 150 has a standard Vixen-style dovetail plate attached to the bottom, running the full length of the tube.
The Skymax 150 is sold as an optical tube only, so the default expectation is that you have to shop for other stuff, to begin with. Thus, we can’t really complain too much about the included accessories, as they’re essentially a bonus.
The Skymax 150 uses a proprietary threaded visual back and comes equipped with a 2” mirror star diagonal which inserts directly into it. It’s a nice, if basic, diagonal without dielectric coatings or a compression ring to hold eyepieces, As previously noted, the Skymax 150 cannot actually illuminate a 2” eyepiece field fully, so it might be a good idea to replace the diagonal with a high-quality 1.25” unit to save on weight and space requirements, which can be critical if you are purchasing this scope for travel.
A single, 28mm focal length, 2” “LET” eyepiece is included, which provides 64x with the Skymax 150. The LET design is basically a Kellner with a roughly 55-degree apparent field of view. Technically, there’s no reason for it to be a 2” eyepiece at all, as the true field is about the same as a typical 32mm, 1.25” Plossl eyepiece. It works well, but again, it’s unlikely you’ll be using any other 2” eyepieces with this scope.
For a finder, the Skymax 150 is provided with a 9×50 straight-through unit. It’ll show you stars a few magnitudes fainter than what you can see with the naked eye, between magnitudes 7 and 10 or so, depending on your light pollution conditions. The field of view is about 5 degrees, and the view is flipped upside down. While a finder like this could be considered overkill on a telescope mainly aimed at easy targets like the Moon and planets, the narrow field of view of the Skymax 150 means that a super-accurate finder like a 9×50 can save you a bit of frustration.
The Skymax 150 is just small and light enough that smaller non-GoTo mounts are still an option. For casual viewing, an Explore Scientific Twilight I or Stellarvue M002C would probably be our pick. If you want an equatorial mount, a Celestron CG-4 or Sky-Watcher HEQ5 Pro is a good choice. You need something with at least a 20 lb capacity, as the Skymax 150 on its own weighs 14 lbs, and it’s not a good idea to push the limits of a smaller mount, especially with a scope meant for high magnifications where a jiggly setup can seriously detract from the view.
Should I buy a Used Sky-Watcher Skymax 150?
A used Skymax 150 is a great scope. Make sure that the optics are in good condition and the focuser works, and you’re good to go.
Aftermarket Accessory Recommendations
The Skymax 150 would benefit from a dew shield. A dew shield prevents condensation from forming on the front corrector lens, which can fog up views and damage the corrector lens over time, as dew is acidic. It also helps to improve contrast by shielding the telescope from off-axis light and stray light from your surroundings, in a similar manner to a lens shade. You can make one yourself out of a variety of materials, or purchase one that slips onto the front of the tube.
Planetary imaging with the Skymax 150 is best accomplished with a high-res, high-speed CMOS video camera designed specifically for the task. Our favorites in this category are the ZWO ASI224MC and ASI120MC, coupled with a 2x or so Barlow lens/focal extender to bring the Skymax 150 to an optimal focal ratio and image scale somewhere between f/20 and f/30 to take advantage of the pixel size and frame rate of these cameras. The Apertura 2.5x Barlow lens or the more expensive Tele-Vue 2.5x Powermate (both 1.25”) will bring the Skymax 150 up to f/30 and 4500mm, a little on the high side, while an Explore Scientific 2x Focal Extender or Tele-Vue 2x Barlow lens provides a more reasonable f/24 and 3600mm. We would not recommend going above f/30 due to the low brightness, diminishing returns in image quality, and difficulty in aiming or focusing the Skymax 150 at such a long focal length. The cheaper 2x achromatic Barlow lenses on the market, which are meant for visual use are less-than-ideal for imaging with the Skymax 150, though they will suffice if you are on a very low budget.
Choosing eyepieces for a telescope like the Skymax 150 is really a matter of personal choice, but at the bare minimum, something around 8–10mm to complement the included 28mm LET ocular would be a good idea. Our favorite picks for these would be a 9mm “redline” or “goldline” (200x) or an 8mm Agena Starguider (225x). If you buy a Barlow or focal extender for imaging, these can be used to amplify magnification as well and replace a high-power eyepiece or two in your collection-so something like a 15mm Starguider or redline/goldline (120x, or 240x with a 2x Barlow/extender) might be all you need.
What can you see with Skymax 150?
Because of the Skymax 150’s narrow field of view, you’re a little more limited when it comes to viewing deep-sky objects compared to typical scopes of this aperture. Many larger open clusters look great, but won’t fit in the field, as will a lot of nebulae. Galaxies look great under dark skies – you can start to see the dust lanes and spiral arms in a few, such as M51 or M64, and the Virgo Cluster never disappoints. 6” of aperture is enough to resolve globular clusters like M13, and a few planetary nebulae will start to show color and fine detail.
Where a Maksutov-Cassegrain really shines, however, is on small targets like the Moon, planets, and double stars. The Moon will show features just a couple of miles wide, including tens of thousands of tiny craterlets, mountain ranges galore, faults and cracks in the surface, and, of course, the larger craters and their central peaks.
Seeing the phases of Venus and Mercury is a given with almost any telescope, of course, but the Skymax 150 does a wonderful job of resolving tiny details on Mars’ surface too. You should be able to pick out the polar ice caps almost all the time, and when Mars is close to Earth in the months around opposition, up to a half dozen or so dark patches should be visible at medium-high magnification on a clear and steady night.
The Skymax 150 easily reveals the colorful and constantly changing cloud belts, polar zones, storms, and festoons of Jupiter. Jupiter’s moons appear as small disks with jet-black shadows following them during their frequent transits, and the Great Red Spot is fairly easy to see. Saturn shows some dull ruddy cloud bands, its rings, and the Cassini Division within them, along with a handful of moons. Uranus and Neptune are nothing but teal and deep blue dots, respectively, often hard to distinguish from stars, especially at low magnification, though Triton might be visible next to Neptune at high power on a dark night if you look for it.
Double stars are impressive with the Skymax 150 under good conditions; there is no chromatic aberration nor any diffraction spikes to spoil the view, so you can resolve sub-arcsecond pairs with a steady enough atmosphere.