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Skywatcher 120/600 Short Tube Achromatic Refractor


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Background Information

I'm an amateur astronomer in Austria, having reignited my interest in the hobby some seven years ago, by purchasing a Synta 50mm, single lens objective scope, and a couple of years later a Skywatcher 90mm Maksutov. I don't drive, so portability is an important factor for me. While the Mak is not much more to carry than the little Synta - except for the tripod - the difference in optical quality is profound enough that the Mak kept me happily, if infrequently, observing over the years.

However, the relatively narrow field of view and poor contrast of the Mak led me to consider a new purchase. I was particularly disappointed that I couldn't get the whole of Pleiades into view with the scope's 25mm supplied Kellner eyepiece, and I didn't bother to upgrade to something like a 32mm Plössl, since I understood there would be vignetting. In addition, even though I have upgraded to a 9mm Ortho for planetary viewing, I've never seen more than two main belts on Jupiter, and seeing the Giant Red Spot took painstaking observation to satisfy myself I wasn't imagining it. Yet, I have fond memories of a 5" Newtonian I built with help from a craftsman when I was a teenager. I wanted to repeat that level of observing experience, but with something more portable.

After a lot of research, including reading reviews and the forums at CloudyNights, I settled on a Skywatcher Short Tube achromatic refractor. I really would have liked 6" apperture, but that model is too heavy and too long for me to comfortably carry. The next model down, 120/600 seemed a perfect compromise, and I purchased it online from Teleskop Service in Germany, together with a 2" TS 99% Dielectric diagonal, a 2" 30mm TS Erfle eyepiece (basic 5 lens design, but fully multicoated), and the Baader 2" ContrastBooster filter.

Please note I have no affiliation with either the manufacturers or the vendor, I'm merely a customer.

The Telescope Package

There were two types of pictures I have been seeing of this scope: the old blue version, and a new brown one, with some black trimming. I expected to receive the brown version, but what was actually delivered was in the new Black Diamond style, with a dark brown tube, and white dew shield, tube rings and focuser mounting. Seeing it in person, I like this style a lot, even though when I saw the rest of the BD lineup at Skywatcher's website, I didn't think it was appealing.

All was in order when I received the package, and some of the components were already familiar to me from the Maksutov. As soon as I began assembling the telescope on the included AZ3 mount and tripod, I began to notice some things that seemed odd.

The two screws attaching the tube rings to the mount have the regular screw heads. The two screws with handling knobs that you see in the picture are from the Mak. I don't understand how Skywatcher could have supplied regular screws in this way - I would hate to have to deal with them with cold fingers on a winter's night.

The AZ3 mount's Altitude (up-down) axis has no adjustment or locking knob, such as is found on the Azimuth axis. Such a knob could serve as a handle, so to move the scope up or down, you need to hold the scope, which is not ideal. There is an inherent lack of balance on this axis, and I found the best compromise was to mount the scope as far to the front of the tube rings as possible. The scope can't trip forwards, there is a stop that prevents it tilting below the horizontal line. Even so, when tilted toward the zenith, the imbalance turns to the focuser side, and the scope is wont to tip backwards. This is a more serious problem, as it could hit a tripod leg with the diagonal. Fortunately, the whole thing is managed well enough by adjustable tension in the Alt axis. However, as delivered, that tension was 100%, I couldn't move the scope. Trying the tools included with the package, I found that the tensioning bolt was too big for all of them. I managed to loosen the bolt and adjust the tension to an acceptable level with my own tools, making sure that the scope was both moveable easily enough, but would also stay in position when pointing near the zenith. Initially I was afraid the tension would loosen in use, but after 3 observing sessions, I find this doesn't seem to be happening.

I had the completely wrong idea about the dew shield, thinking it was thin plastic or aluminium and retractable. Well, it's made of thick metal, and isn't retractable, for a good reason: the objective is mounted inside it. That means no user collimation is possible and if you try to unscrew the dew shield from the tube, the lens comes off with it. At first I thought that was what I would be doing for transport, because with the dew shield not being retractable, the scope was too long for the bag I wanted to use. However, I came to the better solution of unscrewing the focuser rings at the other end of the tube, and now the scope fits in the bag very snugly.

In every other way the scope was as expected. Or better even: I noted that the two supplied eyepieces are now Plössls, not Kellners as was the case with the Mak. Also, the tripod I received seems to have thicker and sturdier legs than the one I received with the Mak's EQ1 mount. But I found it still shakes badly enough to make focusing at higher powers a challenge. Lastly, a 45 degree upright prism diagonal is provided. The diagonal and the eyepieces are 1.25", fitting the 1.25" reducer in the 2" rack and pinion focuser. The focuser feels solid and of reasonable quality, though it does have a very slight amount of play. And yes, that infamous "Synta grease" is there on the drawtube teeth. This can be annoying if you touch it when trying to move the scope, and the gunk is difficult to get off your fingers. I've cleared as much of it as I could with a cloth. What a "nice" reminder of that 50mm Synta scope I used to have... Really, I would have thought that after all the years of users complaining about this grease, Synta/Skywatcher would have got the message.

Observation

My observing notes are based on the best views obtained in 3 observing sessions over two nights in late August, varying in seeing and transparency from average to excellent, with up to 6 limiting magnitude.

One of the first things I did with the scope was a star test. This revealed well collimated optics with no quality issues, except for one: when using long focal length eyepieces with the 2" diagonal, the extended path the light must travel means that the drawtube must be retracted further inside the main tube to achieve focus than with a 1.25" diagonal. That results in the frontmost baffle in the draw tube stopping the aperture down to about 110mm. Wide angle vistas viewed through the 30mm Erfle mounted in the 2" diagonal lacked punch when compared with the bright and contrasty views I obtained with the 10mm eyepiece.

Moon: I was very pleased to note that colour abberration was minimal at low to medium powers. Crisp, contrasty views, superior to the 90mm Mak. The Mak's supplied 25mm Kellner suffered badly from light "blooms" cast by bright objects, but the 25mm Plössl supplied with the 120mm ST has no such problems. Viewing the moon with a 2x Barlow and 9mm Ortho made the violet halo a lot more obvious, but not intrusive enough to spoil the 133x magnified view. The features were still well defined and contrasty enough.

Jupiter: the biggest, shocking surprise of all - the best view of the planet I've ever had! But, I hasten to add, not with the supplied accessories. It was Jupiter that conclusively revealed how useless the supplied 1.25" prism diagonal is for astronomical viewing. The view is comparatively dim and unsharp, revealing no more than the 2 main belts on Jupiter. In addition, there is a horizontal line of light cast across the whole field of view by the planet - weird and unacceptable. I had used the prism diagonal in the hope that, as had been reported in the forums, there may be an improvement in image quality, but that was not the case with this setup. For the view that so pleasantly surprised me I was using the 1.25" mirror diagonal from the Maksutov, 2x Barlow and 9mm Ortho, for 133x power. Four cloud bands were seen, with mottling and waves in the main two, and the GRS not merely a cut into the dark belt above it, but a distinct object in its own right, of pale pink colour. There was a small dark oval to one side of it, and another in the belt directly above. During moments of still air, the planet looked its characteristic self, rather than me having to stretch my imagination for the effect. I found the purple halo quite irrelevant, it was the difference in focus between green and red colours that provided more of a challenge. But that challenge seemed to solve itself when viewing the object perfectly on-axis. As soon as my head moved slightly to the side, a red fringe could be seen and detail reduced. Yet, every instant that I was able to hold the planet on-axis, it appeared sharply defined and detailed, a pale disk with no colour fringe other than the purple halo. The contrast was much superior to that offered by the 90mm Mak. In comparison with the setup described here, the supplied 10mm Plössl didn't offer such a good view, but it got close during one of the sessions when clouds started to move in, reducing the glare of the planet. So perhaps one could see as much as I did, using the Plössl in combination with a neutral density or polarising filter.

I tried using the Baader ContrastBooster filter on both the Moon and Jupiter, but I found I prefer the view without it. The filter does cut the purple halo completely, but it also reduced detail slightly and coloured the view a saturated sepia. Since this filter is said to be most useful on Mars, I'll wait until Mars is in opposition before deciding whether the filter is worth keeping.

M31 Andromeda Galaxy: There was a sharp cut off above the nucleus, which then as a sort of a thin wedge cut into the faint outer disk. I surmised that what I was seeing was the most prominent of the dust lanes, though not as satisfying as I had hoped. I found the companion M110 quite engaging, as it seemed reasonably bright when held in view by itself and had a nicely defined nucleus.

M33 Triangulum Galaxy: A good deal more was seen than in the 90mm Mak, with nebulosity to the sides of the nucleus, and a hint of spiral structure. Nevertheless, it is still mostly just a blob and not very impressive.

M57 Ring Nebula: a lovely sight at 133x power. Difficult to study with direct vision, but in averted view it was startlingly bright and large, with the ring well defined and a hint of differential lighting in places.

M13 Hercules Globular: no great surprises here, stardust all over the place. If the 90mm Maksutov excells at anything, it is at showing globulars such as this. It always resolves them, at least at the edges, with the M13 resolved even in the core. So the 120mm ST offered a brighter view, but not qualitatively much different from the Mak. The difference was more pronounced when viewing dimmer globulars, such as M15 or M92.

M27 Dumbbell Nebula: very nice indeed, with a hint of mottling in the central, brighter, "pinched" section of the oval.

M1 Crab Nebula: for the life of me, I could never find this object with the Maksutov, but with the ST it was easy. That's it, though, I thought it was an uninteresting blob. Admittedly, it was still quite low on my eastern, somewhat light polluted horizon. I'll wait till it's higher in winter, it may offer some detail then.

M82 Cigar Galaxy in Ursa Major: I could see the dusty structures, but not in the way I expected. Instead of seeing the dark spots themselves, it was the bright spots that would pop into view intermittently. Overall, worth taking a look, and it can only improve as it appears higher in the sky later in the year. The nearby M81 by comparison offered no detail.

Double Cluster: a surprisingly satisfying improvement over the 90mm Mak. I think it's to do with the improved brightness of the stars. Observing patterns in the placement of the stars and their colour differences was easier, more could be seen with direct vision. Much the same could be said for other open clusters.

M45 Pleiades: well, here is a lesson learnt. I don't like it! OK, so I finally got my precious view of the entire cluster, but it still failed to impress. The fact that faint nebulosity was definitely seen didn't seem to help. I resigned myself to the realization that it's a problem of scale rather than field of view: the Pleiades look best through a good pair of binoculars.

Milky Way: one of the reasons I bought this scope was to nostalgically repeat an early experience of sweeping the Milky Way with an old pair of millitary 15x80 binoculars on a fork mount. I thought the ST would deliver at least as good an experience. Well, yes, optically it does. The problem, however, is that the ergonomics of the ST setup simply cannot compare to what might be called the "immediate accessibility and control" of those fork-mounted binoculars. The ST tube is too long, the motions of using the AZ3 mount too cumbersome in comparison. I enjoyed sweeping the Milky Way for a short while, but I soon got bored and reverted to the more high-powered views of individual objects.

Conclusion

I would rate this scope 4 out of 5. Optically it exceeded my expectations. It is let down by the prism diagonal and the positioning of the frontmost baffle in the draw tube. The issue of the tube ring mounting screws can't be overlooked either. And the AZ3 mount could use an Alt axis handle. For these reasons, I wouldn't recommend this as a first scope. For those who already have a scope and a few accessories of their own, I highly recommend this ST as the biggest portable scope one can own. For a non-driver, the complete package of the scope and tripod with the mount reach the limits of portability, but the optical quality makes it worthwhile.
  • Davekyn, BinoGuy, Tennessee and 1 other like this


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