Vixen
ED102S Review
Back in the mid-late 1990s, Vixen’s
ED102S was one of the first doublet apochromats to use high-quality ED glass.
Up til then, Vixen and especially Takahashi, had a
history of premium doublet apochromats with crystalline fluorite as the crown,
whilst the US boutique makers specialised in triplets (Astro Physics) and
quadruplets (Tele Vue) to quell false colour. The Chinese manufacturers, which
now dominate ED doublet output, produced only basic achromats back then.
But compared with modern ED doublets, mostly
aimed firmly at wide-field deep-sky imaging, the ED102S was intended for visual
use, especially on the Moon and planets.
I was curious to see how this older
design would compare with more recent ones and especially with the - otherwise
very similar - Vixen 4” fluorite doublet of the time, the FL-102S. Luckily, I
was able to borrow both an FL-102S and a recent SD103S, the ED102S’ successor,
to find out.
Note: I was fortunate to have two
examples to review, one a slightly later model with different (slightly faded)
red graphics. A big thanks to Justin for parting with his collection of classic
Vixens for me to review!
At
A Glance
|
Telescope |
Vixen ED102S |
|
Aperture |
102mm |
|
Focal Length |
920mm |
|
Focal Ratio |
F9 |
|
Length |
915mm w/o visual back |
|
Weight |
4.1Kg incl. rings & dovetail plate |
Data from Me.
Contemporaries:
Vixen ED102S and FL-102S.
Classic and
modern: ED102S and SD103S.
Design
and Build
The original
ED102 was split into two models – the ED102S with a 920mm focal length (F9) on
review here and the ED102SS with an FL of 650mm (F6.4). The style of tube,
focuser and even graphics was the same.
The current
Vixen 4” ED doublet, the SD103S, splits the difference with a focal length of
795mm, whilst the AX103S is a different scope altogether – a quadruplet design
with a triplet objective. The F9 ED doublet lives on in Sky-Watchers’ similar Evostar 100ED.
The ED102S with
the faded graphics in the photos is from the same model era as the later F9
FL-102S, whilst the other ED102S is from the era of the earlier F8.8 FL-102S in
some of the photos. But though the different ED102S variants differ only in
graphics, the two FL-102S versions had different focusers as well as optical
spec’s.
Pedants
please note: I follow Vixen’s own labelling in referring to the ED102S and
SD103S without a hyphen and the FL-102S with.
Objectives: FL and ED.
ED102S (left) and SD103S (right).
Optics
The ED102S appears
(from a laser investigation) to have a conventional foil-spaced Fraunhofer
doublet with the ED crown at the front, as opposed to the fluorite
crown-at-the-back Steinheil FL-102S.
With a focal
length of 920mm and an aperture of 102mm, the ED102S is just slightly over F9.
Those numbers are the same as the newer version of the FL-102S, but not the
older version in some of the images you see here, which had a slightly shorter
focal length of 900mm/F8.8.
I don’t know
for sure, but I’ve seen a film clip purporting to show Vixen’s own lens
factory, so this objective is likely made in house.
With the
current equivalent model, the SD103S, Vixen make a marketing point of
‘Super-Extra-ED’ glass – by which they mean Ohara’s premium FPL53 – so you might
assume this ED102S uses a more basic material for its crown. However, laser
scatter from the crowns looks identical; it’s the flints that appear different
– the flint in the SD103S (on the right above) has slightly less laser scatter
than the ED102S’. Note, too, the thicker crown element of the SD103S due to its
shorter focal length.
Whatever the
ED glass used, given the conservative focal ratio (for a 4” doublet) of F9, I
would expect good correction for chromatic aberrations and so it proves (see
below).
The cast cell,
finished in grey ‘Hammerite’, is exactly like the one
in a current SD103S and is not as sophisticated as the FL-102S’: it is not collimatable and lacks a temperature compensating expansion
gap, though the glass is secured by a threaded ring in the same way. But that
ring isn’t flat-black painted to control reflections like the equivalent in the
FL-102S, let alone the finely ridged one in a Takahashi’s Canon-made cell.
The outer lens
coating looks dark, but reflections suggest that the flint element is uncoated.
All in all,
the objective seems a step down in sophistication from the FL-102S, or a
Takahashi FC-100 or FS-102 of the same era.
Tube
The
aluminium tube is finished in gloss off-white. Finish appears flawless. But
where the early FL-102S has a serial number on its tube sticker, the ED102S has
no unique identifier, like all later Vixens. Also, Vixen’s shade of white
varied over time (or perhaps ages differently): all three, the ED102S, FL102S
and SD103S are slightly different.
The focuser
attaches with screws, but the objective cell threads on for better
orthogonality.
The
dew-shield slides over the cell on felt, a system that may feel less classy
than a thread-on like the FL-102S’, but is actually much more convenient if you
regularly remove it to pack down for travel.
The lens cap
is different from the premium fluorite model’s too – here it pushes over the
lens cell within the dew-shield. It has a 50mm port to stop it down for solar
viewing, as most Japanese refractors (Takahashi included) did in the 1990s.
Internally,
there are a few knife-edge baffles as usual with this style of OTA.
FL-102S
focuser (left) and ED102S.
Focuser
The ED102S
has a different focuser from early FL-102S models (see photo below) – larger
and with a style that’s exactly like many modern Vixen refractors’, apart from
the green ‘Hammerite’ finish. Sky-Watcher Evostars have focusers that look identical too (presumably Synta just copied Vixen’s at some point and have used the
same design ever since).
The focuser
has a cast body with a lock-knob on the top and three bushes adjusted with tiny
Allen screws that are factory-set and sealed. The drawtube is finished in matte
silver. It has a 80mm of travel and ends in (I think!) an M60 thread, so that
the standard 1.25” eyepiece holder should be replaceable with a 2” one.
Like other
Vixens, the knobs are black plastic and the focuser has a cheaper, more
mass-produced look than a Takahashi’s. But functionally this example is smooth
and precise, without significant image shift or slop.
Mounting
This OTA
doesn’t have a mount designation like the older Vixen FL-102S which is labelled
‘Super Polaris’, but it would have been packaged with an SP like the one you
see in the photos, or a GP or GPDX for the later version.
The tube is
long but light and goes fine on a smaller mount. I’ve included a photo on a Vixen
SX2, a more recent mount, which supports it with minimal vibes and would be quite
sufficient for imaging.
Like almost
all Vixens, the rings are formed, not cast or machined. They don’t hinge but
merely tighten with a small gap adjusted with thumb screws. This system makes
them hard to remove, but has the advantage of security (the OTA can’t fall out)
and lightness.
Older Vixen
mounts have fixed plates that attach to the rings directly, but from the GP onwards
it’s the familiar Vixen dovetail.
Vixen 7x50
finder.
Classic
Vixen Lanthanum eyepieces.
Accessories
The older
ED102S came with lots of accessories, including the 7x50 finder and a full set
of period Lanthanum high-eye-relief eyepieces. The drawtube has an adapter for
with a M36.4 thread for the standard 1.25”eyepiece holder, but you can likely
get a 2” one to fit.
In
Use – Daytime
A daytime
snap of branches against the sky at prime focus shows minimal false colour,
giving notice that this is a well corrected lens.
100% crop of
prime focus branches.
In
Use – Astrophotography
With just a
1.25” eyepiece holder, vignetting at full frame is obviously a problem, but
would be less so for APS-C. As noted, you could probably fit a 2” back or use
adapters to thread on a T-adapter directly.
The lens is
slow at F9 and this shows in my standard image, a single unprocessed frame
taken at ISO3200 for 30s with an EOS 6D MkII, of the
Double Cluster. A faster objective would have revealed more faint stars, but
here there is little violet bloat and relatively mild off-axis curvature for a
doublet without a flattener.
The long
focal length means larger image scale that contributes to an excellent image of
the Moon – sharp and full of detail and with minimal false colour fringing on
the limb.
Double
Cluster: ED102S 30S ISO3200 Canon EOS 6D MkII.
In
Use – Observing the Night Sky
General
Observing Notes
I was able
to test the ED102S, FL-102S and a modern SD103S on the same night, swapping
back and forth to compare them. The three scopes were surprisingly similar,
needing high powers to distinguish between them.
A small
gripe, but the inner lens cap of the ED102S is inconvenient: you have to remove
the dew shield to get at it. On one of the two ED102Ss I had for review, a
former owner had fitted a little handle to fix this.
Cool
Down
Cool down
was notably slow for a 4” foil-spaced doublet, with spherical aberration and a
mushy high-power views of Mars for half an hour or so. This is likely due to
the simple cell.
Star
Test
The earlier
ED102S model I tried didn’t have a perfect star test, but the later one was
very good, with nearly identical patterns either side of focus and nice tight
and evenly illuminated rings. As noted, these scopes cool slowly for doublets
and it’s possible I hadn’t left enough time on the first example.
The FL-102S
I was testing at the same time was about the same as the second, as was the
modern SD103S.
The
Moon
At 184x with
a T6 Nagler 5mm, a full Moon was sharp and detailed on the limb where dawn was
still throwing shadows across the mountains to reveal their proper rounded
shape.
Compared to
the FL-102S I was testing at the same time, I noticed a little false colour –
rose and magenta – that the FL avoids and a little more light bleed into the
blackness of space, though the second was perhaps a little better.
Still, a
gibbous 12 day Moon revealed lots of detail in the crater Gassendi,
a personal favourite, the shape of the Messier twins with their double ray, the
crater arc in Clavius and the Mons Gruithuisen dome
field, all in super-sharp and high contrast detail.
There was
more stray light with the full Moon at the field edge than with the FL and some
reflections from somewhere – again, perhaps due to the unbaffled and
glossy-finished lens ring.
Venus
For a 4” ED doublet, the view of Venus was excellent: a small, sharp
gibbous planet with just a trace of gold false colour that the fluorite lens
avoided.
Mars
At 184x with a 5mm Nagler T6, the view of Mars at just 8” across was
good, with Syrtis Major visible centre planet and little false colour: very
comparable with the FL-102S minutes before.
But by 230x with a 4mm Zeiss Abbe Ortho’ I noticed the image in the ED102S
was slightly softer than the FL-102S and markedly lower in contrast too, with a
touch of red false colour blurring into the seeing that was absent through the
fluorite lens. By 263x with a 3.5mm T6, The ED was starting to give a very soft
view. Meanwhile, the FL remained sharp, even with a 3mm Nagler Zoom giving
300x.
However, I thought performance on Mars was a little better than the
SD103S on the same night.
Deep
Sky
Open
clusters like M35-M38 in Auriga and the region around the Double Cluster in
Perseus and Stock 2 in Cassiopeia looked excellent, full of pin-point stars to
the field edge at all powers with flat-field eyepieces like Naglers and Panoptics, but nearly so with basic Plössls too (an advantage of the slow f-ratio). Cooler
stars’ orange colour was strongly delivered.
Despite the
uncoated flint element, the Pleiades were properly dazzling and sparkly
diamonds.
Castor was a
wide and clean split at 184x, but the first diffraction ring was broader and
brighter than the FL-102S’, the second more visible. Still, I easily picked
Rigel B out from the main star’s glare.
Summary
Vixen’s
classic ED102S is a very good implementation of a simple ED apochromat, with
substantially better correction than an early ED Sky-Watcher or even Tele Vue
TV-102.
If you go
looking for it, you can find just a trace more false colour than with the
premium FL-102S, just visible on Mars and Venus and perhaps the limb of a
bright Moon at high power, but mostly chromatic aberrations were better than I
expected from this older design and fully competitive with the modern SD103S.
High power
views are otherwise sharp and detailed, stars nicely pinpoint with dim
diffraction rings and strong natural colour.
The focuser,
similar to so many modern Synta refractors’, looks
basic but works well – plenty of travel, good stability under load and minimal
image shift.
Compared with
a Takahashi FS-102 or FC-100 of the same era, the ED102S benefits from much
lower weight, even if the build quality isn’t as high-end and the optics are a tad
less perfect.
Lacking the cachet of fluorite, the
ED102S was overshadowed by its premium FL-102S stablemate when new, but runs it
quite close in practice and makes a good cheaper alternative for the Moon and
planets.
