Vixen FL80S Review
Thank goodness, we’re over the
worst: in terms of Mars oppositions, at least: 2018 was the closest in this
cycle, but much too low in the sky to give good views from the UK. For the next
few, Mars will be smaller but much more observable.
So, if you’re keen to observe Mars
and you want a small, portable travel scope to do the job, what should you buy?
The problem is that Mars makes particular demands on your scope system. Why?
Because Mars is small, bright and its surface markings are low in contrast.
Also, because it’s red!
Mars’ colour is a problem because many modern refractors are
optimised at short wavelengths for imaging (to avoid bright blue-white stars
‘bloating’ in CCD images). Set a fast ED doublet on Mars and you find it’s hard to focus, the image is soft and a halo
of deep red wafts in the turbulence. This is a deeper problem than simple
chromatic aberration (false colour fringing).
The following graph, of Strehl
ratio (effectively optical quality) at different wavelengths for a fast APO,
explains why they don’t like Mars. To put those Strehl figures into context, 0.95 is excellent, 0.80 barely
acceptable. So, in the red (and even
yellow to some extent) your expensive, beautifully figured APO lens turns into
a piece of bottle glass!
If you want a small (i.e. 60-90mm)
refractor which avoids that Strehl cliff beyond the yellow
and with premium optics for high magnification on Mars (and a good small APO can show surprising detail on Mars),
what options do you have? Surprisingly
few, it turns out.
One possibility is Vixen’s classic FL series, once available in
a variety of sizes, from 55mm to 102mm. The sweet spot is arguably the FL80 and
the one on test here is the later ‘S’ model. Let’s see if it lives up to the
promise of fluorite performance in a compact package and how it stacks up to
its main rival when new, the Takahashi FS-78.
At
A Glance
|
Telescope |
Vixen FL80 |
|
Aperture |
80mm |
|
Focal Length |
640mm |
|
Focal Ratio |
F8 |
|
Length |
650mm (600mm w/o visual back) |
|
Weight |
2.3 Kg |
Data from Vixen.
Design and Build
Comparisons with the FL80’s big Japanese rival at the time,
the Takahashi FS-78, are inevitable. Compared to the luxurious finish of the
Takahashi, the Vixen FL80 has the same workaday mid-range look common to all
Vixen scopes right up to the present.
The FL80’s focuser knobs are black plastic, as is the focuser
lock-knob; on FS-78’s these are anodised metal. The tube has too many stickers
and the rings are formed rather than Takahashi cast. The hammered green finish
on the metal parts isn’t as premium as Tak’s enamel either. The Tak’ has
that remarkable (and heavy) cast iron manhole cover to shield the lens; the
Vixen has a cheapo plastic cap, like a £100 Vixen kid’s scope. Whilst every
Takahashi has an individual serial number, later Vixens like the FL80 are not
serial numbered (earlier ones were).
That’s not to say the FL80 is poorly made,
far from it: everything is well finished and threads together like the Tak’, rather than push-fit with screws like a cheaper Vixen.
But the FL80 it lacks the thick tubing, lustrous paint and superb castings of
the Takahashi.
However, the good news is that optically the FL80S is right
up with the Takahashi and it’s usefully lighter too, as we will see.
The rear fluorite element in the FL80 is uncoated, as you can
see from the reflections. This isn’t a problem in use.
Looking at the back of the lens, a
laser test confirms the FL80S is a Steinheil doublet with a fluorite rear
element.
Earlier type FL objective has a
proper colimatable cell (this is an FL70S).
Optics
Like the FS-78, the FL80 has a premium F8 Japanese-made
fluorite doublet lens, but note:
· The FS-78 has a Fraunhofer objective,
with the fluorite crown at the front
· The FL80 is a Steinheil with its
fluorite crown at the back (as you can see above), like the Takahashi FC-76
(both old and new types)
· In the FS-78, both elements are
multi-coated, whilst the FL80’s rear fluorite element is uncoated,
resulting in a more reflective lens
· The FS-78 has a colimatable
lens cell, whereas this later FL80 has a fixed-collimation screw-in cell, like
the Takahashi FS-60 (earlier Vixen FLs had adjustable cells)
· Both have foil-spaced elements, not
the large air space you get with some recent fluorite
lenses, like Takahashi’s FOA-60 and Borg’s 90FL
The advantage of the FL80’s minimal cell and lens ring is
reduced weight and a narrower tube and dew-shield (though one unexpected disadvantage is that the FL80 is
back-heavy).
The front surface fluorite design of the FS-78 is probably slightly
better optically, but having the fragile fluorite at the back like the FL80S is
more robust (flint glasses are harder and more resistant to cleaning and dew).
I should mention that the FL series have legendary optical quality.
Bench tests results I have seen suggest that the smaller FL-series have
exceptionally low false colour, well into super-APO territory, which suggests
performance on Mars should be good.
The FLs were expensive scopes new and would be expensive to make
now – check out the prices of fluorite doublets in Taks and Borgs today.
Tube
This FL80S is the newer type, with a short, narrow dewshield
and a fixed lens cell, but with a larger focuser. Earlier example had a larger
tube and dewshield, similar to the FS-78.
The upside of the Vixen’s thinner tube, less substantial
castings and lack of adjustable cell is that it’s smaller
and lighter (600mm long, 90mm diameter, 2.3kg) than the Takahashi FS-78 (750mm
long, 95mm diameter, 2.6kg). In use the weight difference is much more marked,
because all the Vixen ancillaries (rings, finder etc) are lighter too.
These later FLs are a bit more compact than the earlier type
too.
Note: The specs claim 650mm length for the FL80, but with the
2” visual back it’s actually 600mm. By removing the dew-shield the FL80 would
easily pack in a carry-on bag.
Despite its small diameter, the tube has numerous knife-edge
baffles tapering to fit the light cone and Internally
everything has been carefully matte-painted to reduce reflections; this is one
of the most carefully baffled tubes I’ve come across (so much so the baffles
are really hard to photograph).
The Vixen FL80 is significantly smaller than the Takahashi
FS-78 and actually weighs less than a TV-76.
A Vixen FL70S in the old-style tube (the older FL80S looked
identical) with a serial number.
Focuser
The unit on the FL80 was Vixen’s premium focuser in its day:
it has a big drawtube, a cross-cut rack and a Takahashi-like M60 threaded
visual back to allow 1.25” or 2” eyepiece holders and various other accessories
to be threaded on. Like the tube, it has knife-edge baffles to kill ghosting
and help contrast.
That said, it’s single speed and cast-bodied with plastic
knobs. In use the focuser lacks the fluid feel of a Takahashi, but is light,
smooth and accurate and has plenty of travel. It has some image shift on
changing focus direction (just like the FS-78 I tested), but this isn’t
excessive.
The focuser does suffer from a tendency to rack out under
even light loads (though an effective locking knob is provided). In focus travel
is a bit lacking too, and may not be enough for some purposes.
The visual back has a flexible configuration. There are 2”
and 1.25” backs provided. The 1.25” is stopped down in stages from M60 to M54
and then M42 via adapters to allow various accessories to thread in.
Meanwhile, the 2” visual back has some clever features. You
can reverse it to create a thread-in extension tube. Also, the lock ring acts
as a clever camera rotator. If you want to rotate an attached camera or
diagonal, just loosen the ring, rotate the visual back and lock it up again (in
comparison, a Takahashi camera rotator costs ££Big).
The visual back permits several configurations: 1.25”, 2”, 2” plus extension.
The lock ring for the 2” VB acts as a camera rotator – clever!
Mounting
The Vixen comes with a couple of split
(not hinged) rings that have a single ¼-20 thread in each and a Standard
dovetail that fits numerous mounts of all types and sizes. Again, these rings
are less elegant but lighter weight than the trademark Takahashi clamshell.
For testing, I used a Vixen GP mount (on which the FL80 was
originally marketed). On the GP it’s easily possible to use the smallest
counterweight which makes the whole assembly highly portable as a unit (much
more so than the FS-78 on its matching P2Z mount, for example).
I also piggy-backed the FL80 on my AP1200 to really put it
through its paces on a range of targets.
Finder
The FL80 comes with Vixen’s usual small finder that is almost
identical to the SkyWatcher equivalent. Again, it
lacks the premium look and feel of a Takahashi 6x30 or 5x25. The eyepiece
holder is plastic, compared to the knurled metal focuser of the Takahashi 6x30
finder. In other respects, though, the Vixen finder works well: sharp, bright,
with decent eye relief.
In
Use – Daytime
You probably wouldn’t choose the FL80 as a daytime spotter,
but terrestrial performance can reveal a lot about optical performance.
My usual test of tree branches against a bright sky at ~100x
yielded minimal chromatic aberration: in focus there is no false colour; even
focusing through gives a barely detectable cast of purple on one side, green
the other. This level of performance is a significant cut above something like
a TV-76 or a SkyWatcher Equinox 80.
This shot of silhouetted branches through the FL80 (with
inset detail) shows no chromatic aberration.
In
Use – Astrophotography
Images of the Moon and M42 with a Nikon APS-C follow. The
image of the Moon has been cropped; M42 is straight from the camera.
The FL80 produces images of the Moon that are very sharp and
full of contrast. M42 is good too, with well controlled violet bloat. Whilst
curvature is well controlled for a doublet too, you would need a flattener for
serious imaging, especially at full frame.
The Moon in mediocre seeing through FL80 at prime focus with
Nikon 5100.
M42 at prime focus with some sky glow through FL80, straight
from the camera (Nikon 5100).
In
Use – The Night Sky
Cool Down
This is an area where doublets often really win over more
complex designs. The FL80 cools very quickly and benignly. On one recent
evening, I had just a few minutes between storms to enjoy Jupiter in fine
seeing. The FL80 was happily delivering
razor-sharp views at 180x just ten minutes or so from a warm room.
Star Test
The FL80 has an excellent star test with near-identical
patterns either side of focus. Trying the star test on a red star (Albireo)
produced the same result, suggesting the good optical figure is maintained at
longer wavelengths.
There is only the merest hint of chromatic aberration in the
star test, even out of focus on Vega. In this respect the FL80 is as good as
all but the very finest F8 ED triplets.
Despite that non-adjustable cell, collimation is perfect.
The Moon
The FL80 delivered some of the best views of the Moon I have
had in a sub-100mm scope: super sharp, with no chromatic aberration, even at
high power. In the FL80, shadows and space are absolutely black with no flare,
just as they should be. Detail is excellent for the aperture and at 128x with a
5mm Nagler, the Moon just fills the field to give a
superb ‘Lunar Module Porthole’ view.
In fine seeing, the 3.5mm Nagler
giving 182x is quite usable: Like the FS-78, the FL80 takes high magnifications
better than a typical F6 doublet like the TV-76, though at this magnification
getting perfect focus would be easier with a micro-focuser. Perfect focus has
an absolute snap to it.
At 182x the Moon through
the FL80 is still bright and pin-sharp and shows significant detail (I was able
to make out Hadley Rille – a difficult target for a
small scope).
Mars
The red planet was still early in its opposition cycle and so
very small (6” x 9”) when I was reviewing the FL80, however the disk was
sharply resolved with none of the chromatic aberration or softness of focus
that you get with short focal length ED doublets. In good seeing I was able to
make out the bright polar cap at 182x.
Jupiter
At 128x with a 5mm T6 Nagler,
Jupiter was very clean and sharp, with no flare or CA, no ghosting and
considerable detail. At least four belts, the Great Red Spot and polar hoods
could be seen, along with detail in the NEB and SEB at moments of good seeing.
At 182x Jupiter showed masses of detail: fine banding in the
polar hoods, changes of thickness and colour in the main belts and any shadow
transits or dark storms are easy to pick out. The crisp view at 60x per inch of
aperture is a credit to the optical quality of the FL80 and it could doubtless
take 200x or more with a suitable eyepiece in steady seeing.
Neptune
Clearly resolved into a tiny grey disk at just 107x with a
6mm Ethos
Uranus
A small, buff-coloured disk at 107x, with a noticeably warmer
colour than whitish-grey Neptune.
Overall, the FL80 delivers more
planetary detail than many would imagine possible for such a small, lightweight
scope. It’s one of the best planetary grab-n-go’s I’ve tested.
Double Stars
You would expect a high-quality doublet to be good at
splitting doubles and the FL80 certainly is. A 3.1” double in Aquarius from the
ADS catalogue was too easy. The Double Double (Epsilon Lyrae) at 2.3”
gave a perfectly clean split at 107x on both components to yield four tiny hard
Airy disks with black space between - the best I have seen in any scope under
100mm aperture.
Albireo was particularly beautiful with the orange and blue
components bright and vivid. Star colours seem to be a strength of the FL80 for
some reason; the twin orange ‘eyes’ in the centre of the Pleiades were
similarly vivid. This may well be because its perfect optical figure throws all
the available light into the Airy disk, intensifying colour.
Deep Sky
The field of view with an Ethos is virtually coma free to the
edge, with just a little curvature, so star fields and clusters remain bright
and sharp across their extent. The Pleiades were wonderful: dazzling and with
the nebulosity visible at 59x with the Ethos 13mm.
The FL80 gave perhaps the finest view of the Ring Nebula in Lyra
I’ve had in a small scope: at 107x with a 6mm Ethos it
really showed its shape and stood out very well from a flat field of pinpoint
stars. The view was so good I found myself just gazing at it for ages before
remembering I was supposed to be in test mode.
The Dumbbell Nebula was similarly very clearly defined
against a dark sky, with the smoky nebulosity almost 3D. The Crab Nebula was
easy to pick out from its background star field and again looked as good as I
have ever seen it in a small scope.
Autumn is open season for globular clusters, so I tried a few
with the FL80: M02 and M13 were excellent, with the outer stars resolved into
diamond dust; M15 and M56 were less impressive, due to the smaller aperture.
The FL80 must rank amongst the best
small refractors I’ve used for deep sky. The extra 10% light gathering compared to a 76mm and superb
contrast giving better results than I’m used to in a small scope.
Summary
The FL series are a bit of a legend, but if you expected a
harsh reality check in the face of cheap modern competition, you’ve come to the
wrong place.
True the FL80 is, frankly, rather ugly. The dew-shield looks
oddly small and truncated and I’m not keen on all
those big red stickers. The Tak’ FS-78 is in another
league if living-room beauty is your concern and has more of an ‘heirloom’
feel.
The FS-78 also impresses with general build quality and that
fully adjustable lens cell. But here’s the rub: in terms of performance, the FL80 is on a par with the FS-78, whilst
being a lot more compact and yet still very thoughtfully built where it counts.
The two scopes are hard to separate in terms of performance. The larger
aperture of the FL80 – 5% more light gathering than the FS-78 - easily makes up
for that uncoated fluorite element for reach on deep sky.
Of course, the FL80 is a small scope, but every object I set
the FL80 on (and I set it on lots by mounting it on my AP1200 and letting that
find stuff) looked just as good as it possibly could with 80mm aperture. The
planets (Mars included) show more detail than you might expect from a 3-inch
class refractor.
The FL80 would benefit from a better focuser, but the
existing one is adequate, keeps weight down and is very adaptable. That
threaded visual back would allow a slim helical (like a Borg) to be fitted
downstream for fine focussing.
The FL80 is, in my view, another example of where fluorite matters. Turn up the
magnification on a double star or planet (especially Mars) and the FL80
performs noticeably better than a fast ED doublet, even an excellent one like
the TV-76 or TV-85.
Highly recommended,
especially for refractor buffs who value a really perfect
view through their scope (buy the FS-78 for more living-room appeal).
