Sky-Watcher
Equinox 120ED Review
For a balance of performance and
portability, four-inch class refractors have long been my favourite; but for
performance alone, five-inch is the sweet-spot, the size where big refractors
start. Trouble is five-inch refractors have always been expensive.
Sky-Watcher’s 120ED models were the first to change that.
Like me, a friend once owned a
Takahashi FS-128 (perhaps my favourite ever 5” refractor) and regretted letting
it go. But the scope he replaced it
with, the one that he said gave him ‘that same fluorite view’ was a 120ED. At
the time this astonished and intrigued me, especially since the friend was an
experience planetary observer. So I bought one to see
if it really is a budget FS-128.
That friend had bought the basic ED-Pro
version, with a rolled tube and cast focuser much like a Sky-Watcher achromat,
but I went for the premium version – the Equinox – that boasts a CNC tube in
shiny black.
At
A Glance
|
Telescope |
Sky-Watcher
Equinox 120ED |
|
|
Aperture |
120mm |
|
|
Focal
Length |
900mm |
|
|
Focal
Ratio |
F 7.5 |
|
|
Length |
~1000mm |
|
|
Weight |
~6.5 Kg |
|
Data from SW/Me.
What’s
in the Box?
If you buy the 120ED Pro, your crate
contains lots of goodies, like an eyepiece, 2” diagonal and 8x50 finder. But if
you plumped for the deluxe Equinox version, all you get is the OTA and some
rings.
Design
and Build
The 120ED lens is available in two ranges, the ED Pro and the
Equinox.
The ED Pro is the cheaper of the two, with a fixed dew-shield
and a rolled tube in their familiar ‘black diamond’ (i.e. white and metallic
black) colours with a white cast focuser. This was the scope my friend had
bought as a replacement for his FS-128 and I was impressed with its compactness:
here was an almost-five-inch APO that would mount on an EQ5 or equivalent.
Quality was very good, but utilitarian – typical Sky-Watcher.
The other Skywatcher 120ED, the
Equinox on review here, is different. It comes in a shiny black all-CNC tube
with a sliding dewshield and CNC rings and focuser.
The Equinox is about a kilo heavier than the ED Pro, at around 6.5 kg.
Optics
The 120ED lens, a 120mm F7.5 (900mm) APO doublet, is Chinese
made, but the glasses are from premium Japanese/European brands. Sky-Watcher make
much of the fact that they use Ohara’s FPL53 for the positive crown element and a
high-grade negative flint 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.
The big question must be whether the lenses for the ED Pro
and Equinox versions are identical. They share the same specs, but look
different due to the Equinox’s lens ring. My own experiences and
the bench tests I have seen might
suggest that the Equinox lenses are better and it’s certainly possible that
Sky-Watcher select the best lenses off the line for the premium tube. But I have no conclusive evidence.
One final point is that some testers have noted vignetting on
the 120ED that means it’s really something like a 114mm F8. I didn’t test this
and so can’t comment.
Tube
Full size pick-up trucks: Americans love ‘em and there’s an imported one around the corner from me –
shiny black with acres 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.
In fact, the Equinox is beautifully
built, whatever you think of the shiny finish. What looks like chrome is chrome, i.e. metal and not plastic
(though I’ve since heard it flakes off easily). 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 looks a bit cheap and flashy, but isn’t.
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 Equinox focuser is a standard premium 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 throws in a final feature anyone using refractors
on equatorial mounts will appreciate: a rotator for the focuser. The knurled chrome
ring in front of the focuser twists to allow the whole focuser to be rotated. It’s
intended as a camera rotator – allowing perfect framing for imaging. But I love
rotators for visual use: you can get a perfect eyepiece position without
risking dumping any expensive glass on the floor. The Equinox rotator is a bit
stiff and not so smooth, but is still a handy feature.
Mounting
Sky-Watcher supply the Equinox with a pair of quality CNC
tube rings with various pre-tapped holes, including the 80mm (3.2”) pair of
¼-20 threads to fit Astro-Physics plates. That’s handy for me, because it fits
the big permanent plate on my AP1200 mount (see below). Given the all-CNC build
of the Equinox, that means it’s orthogonal enough for aligning the AP1200 (no
counterweight required). If you have a goto mount to
align, that orthogonality (exact alignment of mechanical and optical axes) may
be a factor over the less precisely fabricated ED Pro.
The AP1200 is
clearly overkill, but the Equinox does really need a larger mount than the ED
Pro - its weight tips it past the ideal for an EQ5. My old Vixen GP (basically
an EQ5) did work with the Equinox, but only just. A medium mount would be more
stable and track better, especially for imaging.
For visual
use, I found a Tele Vue Gibraltar made a very stable
platform for the Equinox and looked good doing it. Other larger alt-az mounts should work fine.
Sky-Watcher
Equinox 120ED has CNC rings that mount straight on an Astro-Physics plate. The
all-CNC OTA is orthogonal enough to align the AP1200 mount.
Accessories
Unlike the well-spec’d 120 ED Pro, the
Equinox comes only with rings (incl. vixen-style plate) and case. But both are
of a higher quality. The Equinox’s rings are CNC, not cast. The case is finer quality and lined with
proper foam not packaging style ethafoam, like the
ED-Pro’s.
The Equinox version of Sky-Watcher’s
120ED comes with fewer accessories, but a finer 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. For a 120mm ED doublet at
F7.5 this 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 and
deep-sky images later confirmed: this lens is tuned for the mid-visual
wavelengths at which the eye is most sensitive.
In
Use – Astrophotography
For APS-C sized chips at least, the
120ED has a reasonably flat field and good coverage, but the (hazy) single
one-minute frame of M42 below shows significant violet bloating, revealing
chromatic aberrations that visual use doesn’t.
Like most good apochromatic refractors,
the flat field and sharp optics of the 120ED produce great images of the Moon,
with lots of detail limb-to-limb.
In
Use – The Night Sky
General
Observing Notes
The Equinox
is an easy and un-fussy observing tool: smooth focuser, snappy optics,
well-corrected field and moderate focal length means it gives great views with
most eyepieces.
Cool
Down
One big advantage of a doublet at this
size is that it cools quite fast. In comparison a 120mm triplet (like my
FLT-123) cools very slowly. You could use a 120ED as a quick-look scope,
whereas an FLT-123 or Tak’ TSA-120 (and probably an
Esprit 120) you could not.
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.
The
Moon
The field is wide and flat enough, the focal length still
short enough, to enjoy the whole Moon, something SCTs do less well. It’s a
great view – detailed enough to give that ‘Command Module porthole’ effect with
a wide field eyepiece that smaller refractors can’t achieve. Even at 150x with
a 6mm Ethos, the view is still very sharp and detailed with just a trace of
chromatic aberration visible when focusing through the limb.
At this aperture a lot of fine Lunar detail is available to
explore – wrinkle ridges and craterlets, rilles and
domes. Typical of a fine refractor, contrast is outstanding and stray light
well controlled, even around the bright limb.
Mars
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 Takahashi
FS-102 or TMB 100/8; aperture wins here.
One negative point was a faint reddish
glow of unfocused light around Mars. I had seen this with the 100ED as well.
Mars also generated some chromatic aberration not seen on most objects, very
obvious either side of focus: green-blue on one side, red on the other. Again, I
suspect this is because the lens has been tuned to middling visual wavelengths.
Saturn
Saturn looked great through the 120ED,
showing the kind of detail, including the polar hood and Cassini Division, that
I recalled through the Tele Vue NP-127. On Saturn,
false colour wasn’t a problem, though I noted some minor colour either side of
focus.
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.
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 apochromatic refractor
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.
Clusters and nebulae look really good with the extra aperture over smaller refractors,
but it’s the sharp high-power planetary images and good contrast that really stand out.
No, it’s not (quite) in the premium league of an FS-128,
showing a bit more chromatic aberration and stray light, especially on Mars (though Red Planet views are still very good).
Similarly, some violet bloat might be a problem for deep sky imaging.
The bottom line is that the 120ED gives owners a chance to
own and try a high quality apochromat for a very low price. For a planetary
observer in an area with mediocre seeing, it’s
a particularly fine budget choice; indeed, arguably better than a premium four inch refractor if portability isn’t an issue.
One final question is ED Pro or Equinox? That depends on the
price difference. Currently the Equinox is widely discounted to within about
20% of the price of the ED Pro. For the extra, I’d buy the Equinox.
Sky-Watcher’s Equinox 120 ED gets my highest recommendation
as a premium larger apochromat for a very reasonable price.
Updated by Roger Vine 2018