Skywatcher Equinox 120ED Review

 

A strange thing happened to me about a year ago: I bought a Tele Vue NP101, a high-end 4” APO refractor.

Well it wasn’t the buying of the Tele Vue that was strange, but rather the circumstances around it. My observing pal had just sold a Tele Vue mount to a well-known planetary observer from Lancashire, who had brought along his prized TV NP101 Refractor when he travelled up to collect the mount.

My observing pal had previously owned and loved my own TV Genesis and was curious about the NP101. He reported to me excitedly what a marvellous thing it was (wide flat field, zero CA, super sharp etc) and how impressed this planetary observer was with it. Then, a couple of weeks later, the NP101 was mysteriously put up for sale.

My friend couldn’t understand the situation: the owner had been so enthused about the NP101, had bought it new and only owned it for a year. What was going on?

I contacted the owner of the NP101 and asked why he was selling it. I learned that the sale was due to nostalgia for a previous scope – a Takahashi FS-128 – which the NP101 had never quite matched. The FS-128, he explained, had given him his best views of Mars and he had always missed its razor-sharp, high-contrast views. Now he had finally found a replacement for the Takahashi – one that gave him ‘that fluorite view’ - so the NP101 was being sold to make way for it.

I had owned an FS-128 for a number of years and knew very well what a fine planetary scope it was, so the story seemed plausible. So what was this replacement the man had found for the planetary prowess of Takahashi’s legendary FS-128? A TMB 130 F9 perhaps? Had he found a 5” ApoMax for sale somewhere? Maybe he’d finally got to the end of the decade long wait for an AP 130? He finally admitted, a little sheepishly I thought, that he and his mate, another highly experienced observer, had both bought the then-new Skywatcher 120 ED.

Friend and I spent many an evening over a pint afterwards discussing why on earth anyone would replace a Tele Vue with a Sky-Watcher, especially for planets, which demand high optical quality. A sneaking suspicion crept over us both that the man from Lancashire had discovered some secret.

Over the next year I noticed that whilst plenty of 120EDs were apparently being sold new, none were coming up secondhand. Then one did (in Lancashire, funnily enough), so I bought it in order to find out what the secret was and share it …

At A Glance

Telescope

Sky-Watcher Equinox 120ED

Aperture

120mm

Focal Length

900mm

Focal Ratio

F 7.5

Length

~1000mm

Weight

~6.5 Kg

 

Design and Build

Lens

Coatings look good, but the cell isn’t collimatable.

The 120ED lens, a 120mm F7.5 (900mm) APO doublet, is Chinese made and one of the largest they currently produce. The adverts are at pains to stress that the glasses used are FPL53 for the positive element and a high-grade crown from Schott. Now FPL53 is one of the best high-fluoride ED glasses around. Astro-Physics use it in their scopes. But a lens is much more than its component glasses - even more important are the quality of the grinding and polishing and careful assembly (which is critical for an APO).

I don’t want to pre-empt the review, but a well-known German optical tester reckoned that the 120 Equinox he tested was close to 1/8th wave PV – supreme optical quality at any price point.

If the Chinese fabricator has gone to the lengths of using quality glasses, he certainly hasn’t skimped on coatings either – my 120ED has dark green multi-coatings that are perhaps just a bit more reflective than the very finest, but not much. The lens just about fills the tube – no room for a collimatable cell.

Tube

The 120ED lens is currently available in two ranges, the ED Pro and the Equinox. The ED Pro is the cheaper of the two, with a fixed dew-shield OTA in their ‘black diamond’ colours. I had seen this scope when the owner delivered the NP101 and was impressed with its build quality and compactness: here was an almost-five-inch APO that would mount on an EQ5 or equivalent. The other Skywatcher 120ED, called the Equinox, comes in a shiny black all-CNC tube with a sliding dewshield and CNC rings. The Equinox is about a kilo heavier than the ED Pro, at around 6.5 kg.

Full size pick-up trucks: the Americans still love ‘em and they’re just the thing for stocking up your red-dirt ranch on the Utah strip. You see rows of them lined up in KMarts and WalMarts out West, big ol’ boys loading them up with crates of Mountain Dew. There’s an imported one ‘round the corner from me – shiny black with masses of chrome. The Equinox is much the same, with lots of piano-black, too many chrome parts and a general level of shininess that I don’t like in pickups, never mind telescopes.

Given that the Equinox is 30-40% more expensive than the ED Pro and heavier to boot I had always thought I’d buy the cheaper scope if one came up. Unfortunately, an ED Pro never did come up for sale, so the Equinox had to do.

I’ll admit I was wrong about the build quality of the Equinox, though. Most of what looks like chrome is chrome, i.e. metal and not plastic at all. The tube may look so shiny that it must be plastic, but it isn’t - it’s beautifully anodised metal too, which is why the Equinox is heavy. In fact it’s fair to say that the external build quality of the Equinox is almost too good, too honed and polished; it still looks a bit cheap and flashy as the result, but much less so than in pictures. Whatever you think of the black-and-chrome livery, this is a very well made telescope. Look past the lens (easy to do with those coatings) and you find a set of knife-edge baffles finished in matte black and a generally high level of internal quality as well.

Focuser

The focuser on the 120ED is a standard Chinese Crayford with a dual speed knob on the right. The focuser may be the only part of the 120ED that actually contains plastic (the pinion shroud), but mostly it’s anodised CNC-machined metal too and very precise and smooth in operation.  I can detect no play in the drawtube, even at full stretch, which is great news if (like me) you want good pointing accuracy on a goto mount. Not only is it smooth, but the focuser has a huge 13.5cm of travel, with a scale to tell you how far out you’ve got. The focuser remains smooth, even with heavy eyepieces.

The Equinox series throw in one final feature that anyone used to using refractors on equatorial mounts will appreciate: a rotator for the focuser. The tacky-looking (again it’s actually metal) shiny ring in front of the focuser twists to allow the whole focuser to be rotated to the most convenient position without fear of dumping the diagonal or scratching its barrel. This is a feature I love in the big Starlight Instruments focuser on my TMB 175 and though the one on the Equinox isn’t in the same league (the big Feathertouch is like a professional instrument and costs as much as the whole Equinox 120ED) and is a bit stiff and jerky, it is still a handy feature.

Accessories

Nestling in its good-quality standard hard case, the 120ED looks very small for a five inch class refractor. This is because it has a sliding dewshield that permits a folded size of about 31 inches and the tube outside diameter is the bare 120mm. The lens looks much bigger than you expect given the tube dimensions. Slide out the (very stiff to move) dew shield and it looks more like the big refractor it is. But the Equinox still mounts on a Vixen GP – a huge advantage over most scopes this size (the FS-128 needs at least an EQ6). Talking of mounting it, a pair of well-made CNC tube rings are provided with various pre-tapped holes, including the 80mm (3.2”) pair of ¼-20 threads to fit Astro-Physics plates.

The Equinox is a good fit on Tele Vue’s Gibraltar 5.

Apart from those rings, the Equinox is a bare OTA. Unlike the cheaper ED Pro it comes with neither finder, nor diagonal, nor eyepiece.

The Equinox in its standard hard case.

In Use - Daytime

I may not like the shiny piano-black mass-produced flat-screen-TV consume-then-discard appearance of the Equinox, but I have to admit the build quality is exceptional for the price. So what’s it like in use?

Obviously the 120ED is an astronomical telescope, not a spotter, but daytime views can be revealing of optical quality.

During the day, my standard CA test at 100x on high branches in silhouette against the sky revealed a surprisingly low level of visible CA. Even out of focus, there is negligible false colour at a level reminiscent of a fine triplet. For a 120mm ED doublet at F7.5 this level of CA is surprising; consider that Takahashi have used an ED triplet with identical specifications in the TSA 120. This result suggests that the lens designer of the 120ED has pulled an entirely legitimate “trick” here, something that views of Mars later confirmed.

In Use – The Night Sky

The day after I picked up the 120ED, from a snowy town in Lancashire, the skies miraculously cleared. A cold, but dark and still night of viewing and testing beckoned. I mounted the Equinox up on my old Vixen GP and let it cool for an hour. Despite the 6kg weight of the OTA, the Vixen coped well and with manageable vibes, even at high power. This is a significant thing. Very few five-inch class APOs are available that will mount on an equatorial as portable as the GP.

Star Test

A star test revealed very similar images inside and outside focus, with very equal illumination and no collimation problems. In fact the star test is one of the best I have seen, confirming the bench-test results I’d read.

Deep Sky

I limbered up for the observing session with the Equinox by taking a look at some easy DSOs: the Orion nebula, the Double Cluster and M31 in Andromeda. All of these targets looked excellent, pretty much the way they do in any fine medium-sized APO, with more intense star colours and more nebulosity structure than in a smaller refractor, but still with a wide field. At this aperture, the Great Nebula in Orion does look a lot more interesting than in say an 80mm, with the Trapezium perfectly resolved even at low power within a mass of nebular whirls and knots.

Next, I decided to try a double star. It was possible to pick out Rigel B from the glittering diffraction rings of Rigel A, even at just 70x. Other casual doubles, such as Castor and the Pole Star, split very nicely too, with tight airy disks.

Planets

Turning to Mars, I was able to push the magnification to 300x with excellent detail visible in the albedo markings and good focus snap (the focuser is very precise at high powers) and with none of the “fuzzy orange ball” effect you often get on the Red Planet. I could clearly see the north polar cap and Syrtis Major. Later in the evening, Solis Lacus and Mare Acidalium were easy to pick out from the orange disk, with very good sharpness and contrast. The 120ED was offering better high power views of Mars, with detail more easily seen, than I recall in either my FS102 or TMB 100/8; aperture wins here.

 

A slight negative point was a faint reddish glow of unfocused light around Mars. This didn’t affect the view of the planet itself and was caused by chromatic aberration not seen on most objects, but which was very obvious on Mars either side of focus: green-blue on one side, red on the other. I suspect this is because the lens has been tuned to the shorter wavelengths to avoid violet bloat on O-B type stars for astrophotography.

 

Out of interest, I tried the same magnification on Mars in my FS128 on the same night and there was no visible chromatic aberration or spherochromatism at all. So, good though the 120ED is, it’s not an FS-128 (nor, obviously is it the price of an FS-128, even used).

 

Saturn was too low to give an accurate impression, but looked similar to the view through my NP127 on the previous night.

 

The Moon

 

Views of the 3-day Moon were good, but it was again too low to get a true impression with high magnifications and the bitter cold (below minus five) forced me inside before I had spent much time with it. The following was the best snap of the Moon I managed through the 120ED:

 

Equinox Moon

I should just finish by saying that I found another use for the 120ED – drift aligning my AP1200 mount. Hard experience had taught me that anything other than near perfect orthogonality leads to problems when drift aligning and most scopes fail the test. What is needed is a CNC tube, CNC focuser free from image shift and CNC rings that bolt directly to AP’s plate, with enough tube length to allow the rings to be spaced 14” apart on the plate. Few scopes offer this: the big TMB does, but it’s too long to safely allow it to meridian swap, a part of the procedure; the 120ED is perfect for this task and after just a few hours I had my best ever alignment on the AP1200.

Summary

For those familiar with Sky-Watcher’s somewhat agricultural achromatic refractors, the Equinox is a big surprise. Build quality is more that of a mass-produced consumer item than the small-volume feel of a Tele Vue or a Takahashi, but is very good. At one time even a basic good-quality five inch APO OTA would have cost upwards of three thousand pounds new, but the Equinox is less than half that and throws in some very nice features like the dual-speed rotatable focuser, sliding dew shield, CNC rings and case.

Optically, the Equinox appears to be of very high quality indeed and in use it works very well in all respects. Clusters and nebulae look really good with the extra aperture over smaller APOs, but it’s the sharp high-power planetary images and good contrast that really stand out. The views are very enjoyable (much, much better than most SCTs I have seen), with excellent performance on most types of objects, including Mars (an object which troubles many scopes). No, it’s not (quite) in the premium league of an FS128, showing a bit more chromatic aberration, especially on Mars.

The bottom line is that the 120ED gives owners a chance to own and try a high quality APO for a very low price. For a planetary observer in an area with mediocre seeing and/or needing good portability, it’s a particularly fine budget choice; indeed, arguably better than a premium four inch APO.

Addendum 2014: I always said the Equinox 120 was too cheap; it’s gone up by almost 40% since I reviewed it, but remains good value.

Sky-Watcher’s Equinox 120 ED gets my highest recommendation as a premium larger APO for a very reasonable price.

You can buy the Equinox 120ED here: