William
Optics 110 FLT (TEC) Review
FLT-110 with dew-shield extended (see
end photo for retracted).
The Telescope Engineering Company moved
from Kiev to Golden in Colorado some thirty years back and started making
high-end Maksutovs. But by the late 1990s, TEC had
flexed into apochromatic refractors, making their own triplet lenses, often
with a fluorite centre element; their own high-quality tubes and focusers too. If you think of a
cross between Astro Physics and LZOS you’ll get the idea.
TEC specialise in larger triplet
apochromats up to 250mm (10”), but TEC have produced smaller APOs too. Perhaps the most
famous is their 140 (reviewed here). At one time, TEC also made their own 110, called
the Eclipse. It was by all accounts a fantastic little scope – one of
that rare breed of APOs larger than 4” you can carry onto a plane –
but sadly TEC discontinued it for reasons unknown.
Meanwhile, the FLT-110 on review here is the familiar William Optics tube
and focuser, but with a 110mm TEC triplet objective replacing the usual
Chinese one. So this is a budget Eclipse, then? Nope. This objective is
F6.5 (vs F5.6 for the Eclipse) and the centre element is ED glass rather than
the Eclipse’s fluorite.
Still, this is a very interesting scope. Why? Because scopes like this
are rare and most alternatives – TEC’s Eclipse, AP’s Traveler
and their new 110 GTX etc - will cost as much or even more.
At
A Glance
|
Telescope |
|
|
Lens Design |
Oil spaced, ED glass triplet |
|
Aperture |
110mm |
|
Focal Length |
715mm |
|
Focal Ratio |
F6.5 |
|
Length |
575mm/22.6” (553mm/21.8” w/ visual
back unthreaded), |
|
Tube diameter |
115mm (4.5”) |
|
Weight |
5.96Kg tube, 7.32Kg incl. rings, dovetail |
Data from me.
Design
and Build
The tube and focuser are typical of William Optics (i.e. Chinese) fare
from a decade or more ago, a lot like their Megrez scopes. So we have a
heavy-duty CNC-made Crayford focuser with a 3” drawtube, a rotator and a
flexible back threaded onto a nicely finished tube with a sliding dew-shield
and that flashy gold lens ring.
Back in the day, WO made other scopes with objectives from LZOS, LOMO and
TEC alongside their Chinese ones, in small batches when they were available.
All such scopes are likely to be better than their Chinese-lensed equivalents,
but cheaper than the same lenses in scopes in high-end tubes from APM, A&M
and Stellarvue.
The F6.5 FLT-110 with its closest LZOS counterpart
– the TMB 115/805 (F7). Note that the TMB is much longer in use with its
drawtube extended.
Optics
To recap, the objective is what makes this different from most William
Optics scopes of the era. Rather than the F7 Chinese-made objective found in
most FLT-110s, it is a US-made F6.5 110mm oil-spaced triplet.
TEC (unlike, say, Astro Physics) employ fluorite for the centre element
of many of their lenses, including newer versions of both their triplet
and doublet 140 and the superficially similar Eclipse 110. However, this
objective employs ED glass for its centre element. I know this thanks to
testing it with a laser which vanishes in fluorite, but not here. However, I
don’t know which ED glass TEC used.
According to WO, this objective was optimised for the green 546 nm
e-line, roughly where the human eye is most sensitive. This was the standard
approach a quarter of a century ago, when the FLT-110 was designed (Telescope
Optics, Rutten and Van Venrooij, section 6.2).
However, looking at the published crossings, we can see that the 436 nm violet
g-line is less well corrected than a modern fluorite doublet (Takahashi’s
FC-100DZ). This is not an entirely fair comparison, because the FC-100DZ is F8
(vs F6.5) and employs a special dispersion flint, but it does suggest the
FLT-110 might not be up to the best current standards for digital imaging and
so it proves (see the astrophotography section below).
Published crossings for the FLT-110 and FC-100DZ, altered by me to the roughly
the same scale.
Even though this is not a fluorite Eclipse objective, it has a similar
artisanal build, with a beautifully machined and anodised, collimatable
cell and traces of handwriting around the edges of the glass, much like an LZOS
objective. However, also like objectives from LZOS and LOMO, it is a heavy cell
too.
It’s worth commenting on oil-spacing, which is rarely encountered
in recent refractors. In this lens, like say the AP Traveler’s, the three
elements are separated by a thin layer of oil, with similar refractive index to
the glasses, rather than air. This has several advantages:
·
No air spaces means nowhere for moisture to get
trapped and cause problems like fungus
·
The inner surfaces of the elements don’t need
to be as finely polished
·
With all elements in contact, cool-down should be
faster
·
No glass-air boundaries should mean less scatter and
better transmissivity
·
With no foil spacers to slip if jolted, the
objective is potentially more rugged
There are a few possible disadvantages, however. One is oil leakage
– by no means common but not unheard of either. Another is that –
allegedly, I’m unconvinced - the objective may need to be stored flat to
perform to its maximum potential. The third is more of a design constraint -
all the lens surfaces need to be spherical.
Finally, this may be an older lens now, but it is multi-coated and those
coatings look excellent.
Laser reveals the centre crown element is ED glass, not fluorite.
Tube
As I said,
the tube and focuser are like a big Megrez 90. Build quality is very high and
both the cell and focuser thread onto the tube (unlike the TMB above) - good
for orthogonality and collimation.
The tube is
finished in textured powder coat, not paint. Shinier and thinner than the stuff
on a Tele Vue or Astro Physics, it doesn’t seem as robust judging from
the scratches. I’ve personally got used to the signature WO gold accents
on the lens ring and focuser (though I have a friend who dislikes them and I kinda get that too).
The OTA is
quite compact at 553mm/21.8” without the
visual back, almost the same as the (bulkier) TMB 115/805 you see above (and
reviewed here), though
that scope needs its drawtube extending a long way in use. Yes, but is the OTA
small enough to carry on board? After all, that’s one of the main reasons
for buying a scope like this. The answer is maybe: it’s just at the limit, depending on your
airline, but see notes on the case below.
The FLT-110
is fairly heavy at ~6Kg (7.3Kg including the rings and plate), again almost the
same weight as the TMB 115/805. Given its balance point, blame that triplet
objective.
Focuser
The focuser
is a large CNC Crayford unit typical of older William Optics scopes. It’s
smooth, precise and almost free of image shift, has a flexible thread-on visual
back, a rotator and even a scale, plenty of travel too. All good then? Not
quite.
The problem
is that Crayford focusers tend to rack out on their own under heavy loads like
cameras (or large eyepieces come to that). A partial solution is a tension
adjuster that locks the drawtube, but even this can’t fix the problem of
slippage when actually focusing. In this case there isn’t any kind of
lock or tension adjust that I can find.
For imaging
with a heavy camera (and the lens is well up to it) you might consider
replacing the focuser.
Mounting
The
scopes’ short length is in its favour and it’s very stable on my
mid-size Vixen SX (see photos at the start and end of this review), but
it’s just too heavy for smaller mounts, especially once you add a
diagonal and eyepiece or camera (folks often forget this when thinking about
maximum load).
Accessories
The FLT-110 comes with CNC rings and a case (that unfortunately
isn’t quite carry-on size).
I should
point out again that a 4” plus APO you can travel with is rare. If
that’s important to you, you could have a hard case made that just fits
the tube length-wise without much protective padding (with the visual back
unthreaded there’s only about 7mm to spare on BA, for example). See the
example I had made by Thomann for the TMB 115 below.
Could you
get away with the standard case? Just maybe, depending on the airline and how
full the flight is. But the risk is that you have to check it at the gate
(eek)!
Custom
instrument case for the TMB 115 with minimal padding lengthwise for
compactness.
In
Use – Daytime
My usual
test of viewing branches in silhouette at 100x yields almost no false colour
and photos show the same. But you’ll notice some violet bloat in the star
images than other well-corrected scopes. What’s going on?
This is
likely the difference between an objective designed for visual (and perhaps
emulsion) compared to one designed for digital imaging. Visual wavelengths are
well corrected; the far violet, where a sensor is more sensitive than the eye,
less so.
Slightly over-exposed branches show minimal false
colour.
In
Use – Astrophotography
For
imaging, see the notes on the focuser above. I had no trouble with a DSLR,
however. Coverage at full-frame is good with only minor vignetting in the
corners. Field flatness is good for F6.5 too (better than a typical doublet of
this focal ratio), but you would need a flattener for wide-field imaging.
Despite
good correction for false colour for visual use, the B-class stars in the
Pleiades show more violet bloat than the optically similar LZOS 115 F7, confirming
that the g-line might not be as well corrected as I’d like for imaging,
even though this is a very well corrected objective visually. The stars show a
bit of spiking here too, see note on cooldown and star test below.
High
optical quality and a well-corrected field make for a good snap of the Moon at
this modest focal length.
Pleiades: unprocessed full-frame, 60s ISO 3200
Canon EOS 6D MkII.
Comparison of Alcyone and Merope: WO FLT-110
(left), TMB 115/805 (right), both 30s ISO 3200 Canon EOS 6D MkII.
Moon: FLT-110, Canon EOS 6D MkII.
In
Use – Observing the Night Sky
General
Observing Notes
The scope is
very front-heavy due to that TEC triplet. This means you have to extend the
dew-shield and then slide the OTA backwards when you’re mounting it in
the rings.
The dual
speed Crayford focuser has a very fine inner micro focus knob - smooth and
precise, with no image shift and well up to getting perfect focus on the fast
and snappy optic. The rotator is useful visually to get the right eyepiece
position, but a bit stiff under load.
Overall, the
focuser feels stable with its hefty drawtube and smooth action, but shows signs
of wanting to rack out with a 2” diagonal and a T6 Nagler (not an
especially heavy eyepiece). I noted some slippage on the coarse knob too.
Typical of Crayfords, this would be problem for heavy
cameras or eyepieces, unless I can find a tension adjuster!
Cool
Down
Oil-spaced
triplets are supposed to cool faster than air-spaced ones, but fast is relative
here. Compared with a doublet, it’s slow. I could still see tube currents
in the star test after ~1 hour: much the same as the air-cooled 115mm triplet
in my TMB 115/805. See note on the star test.
Star
Test
After an
hour of cooldown there was still some pinching in the star test (note the
slightly spiky stars above), so I left the scope to cool in the car for longer.
Thereafter, the star test (on Pollux) was very good: nicely concentric, evenly
illuminated, sharp rings either side of focus at 143x with a 5mm Nagler, the
outside-focus outer ring just a touch more diffuse. The in-focus Airy Disk was
excellent too, with no sign of decentring or miscollimation.
The
Moon
At 204x
with a 3.5mm Nagler, I had detailed views of Mare Crisium with lots of
craterlets on the smooth lava plains of the floor, the curious hills near the
far rim, odd-shaped Proclus with its breached wall and sweeping ray. Moving
across to large crater Petavius, I explored its
unusual clock-hand rille and the complex of central peaks. Finally, I swapped
to the 3mm setting on a 3-6 Nagler Zoom giving 238x to investigate the bizarre
pair of craters that are the Messier twins, one elongate and with a striped
floor of smooth lava as if whatever caused it grazed the surface at a low
angle.
Stopping
exploring and returning to reviewing, I noted just a trace of false colour
focusing through the bright limb at 200x+.
Jupiter
I had a very good view of Jupiter at 143x with a 5mm Nagler: the polar
hood with delicate banding, thickness variations in both equatorial belts, and
one very obvious dark storm in the NEB. I also spotted the dark shadow of
Ganymede in transit. There was no false colour that I could detect.
On another occasion, I watched a shadow transit of Europa as it crossed
to Jupiter’s limb and exited, at 143x and 204x with both 5mm and 3.5mm T6
Naglers. The bright disk of Europa was clearly picked out against the creamy
cloud belts behind and distant from the small dark spot of its shadow –
majestic stuff! Predictably, I got just a little more contrast and sharpness
out of the 5mm TMB Monocentric – my favourite planetary eyepiece.
Mars
I caught
the Red Planet at an altitude of about 45° and an angular size of 14.5” a week
before the (admittedly unfavourable) 2025 opposition. At 179x with the 4mm
setting on a Nagler Zoom, the FLT-110 showed a sharply defined gibbous planet,
with no softness and just a trace (really) of red blur outside focus and
shimmering into the seeing in focus – similar to an F8 fluorite doublet
and perhaps just a little worse than a typical F6-F7 LZOS triplet.
I was
able to pick up the bright north polar cap, the large dark patch of Mare Acidalium on the western limb, the darker region around
both poles and a dark spike reaching up towards the centre of the disk that I
mistook for Syrtis major but was actually Margaritifer Sinus.
Deep
Sky
The Pleiades
looked lovely with lots of hazy-blue nebulosity (the 21% extra light-gathering
over a 100mm APO noticeable here), with nicely glittery, pin-point stars. The cluster
was perfectly framed by a 19mm Panoptic giving 38x, stars towards the edge of
the field remaining sharp and well-corrected. Stars at the field edge are even
quite sharp in simple eyepieces like Plössls, with much less distortion than a doublet of
similar f-ratio – an advantage of triplet objectives like this one.
I enjoyed
sweeping for clusters in the Milky Way around Cassiopea too – still fun
and easy given the wide field at this focal length.
Easy doubles
like Castor and Rigel were trivial splits, given well-corrected stars with
small Airy disks.
Summary
Even though it’s an old scope now, the TEC-lenses FLT-110 is rare
and desirable, especially as a high-performance portable visual scope. Why?
Because even today there are few scopes around with similar quality and specs.
It is one of the largest-aperture (just about) carry-on scopes and likely
(much) cheaper than a TEC 110 Eclipse (or the old AP Traveler, let alone the
new AP Starfire 110 GTX).
For imaging, the objective is fast for its aperture, well corrected and
with good coverage, but produces a bit more violet-bloat than a modern
objective might. The main issue is the focuser, though. Like many Crayford
focusers, it is smooth and precise, but can rack out under load and
doesn’t appear to have a tension adjuster. It works well for a basic
DSLR, but maybe not for a heavier imaging setup.
When fitted with a TEC objective, the
FLT-110 is a premium APO in a rare and desirable format on the cheap. Highly
recommended, especially as a portable visual scope.
