TEC
APO140ED/FL Mini Review
Telescope Engineering Company’s 140 triplet
apochromat is quite a famous (if you can use that word) scope with a strong
reputation for both quality and sheer multi-purpose usefulness.
This is the latest in a series of mini
reviews where I’ve spent lots of time with a scope and formed a strong opinion
of it, but haven’t been able to put it through the full photo-visual review process.
Note: the
photos in this review are all of the APO140FL at Lowell’s Giovale
Deck Observatory.
At
A Glance
|
Telescope |
TEC APO140ED/FL |
|
Aperture |
140mm |
|
Focal Length |
980mm |
|
Focal Ratio |
F7 |
|
Length |
840mm dew-shield retracted, 1050mm extended |
|
Weight |
8.2Kg OTA (9.5 Kg incl
rings, plate, finder and handle) |
Data from TEC.
The TEC APO140FL
at Lowell’s Giovale Deck Observatory.
Design
and Build
Yuri Petrunin’s
Telescope Engineering Company started in Kiev distributing optical products
from the Russian optical contractors LOMO and LZOS.
Having moved to Golden Colorado, they
started with a range of high-quality Maksutovs and
then in the late 1990s started to get in on the burgeoning market for
apochromatic refractors, making their own lenses tubes and focusers.
TEC currently offer a range of larger
triplet apochromats up to 250mm (10”), of which the 140 is the smallest since
the 110FL was discontinued.
The 140 is by far their most popular product,
perhaps partly because 140mm is an unusual aperture but also a very useful one –
close to the big-refractor performance point of a six-inch, but not much larger
or heavier than something like a Takahashi TSA-120.
Optics
The original
TEC APO140ED had an F7 oil-spaced triplet with an ED glass centre element. A
focal ratio of F7 is ideal for APOs in this size range, allowing near-perfect chromatic
correction with a natively flattish field and still reasonably fast for
imaging.
The original
APO140ED had a great reputation, but still suffered from some residual
chromatic aberrations – false colour fringing and spherochromatism. So when TEC
updated the design in 2017, they swapped to a fluorite centre element for the
triplet. Interestingly, though, they stuck with the oil-spaced design even as
AP were moving away from it.
So what does
‘oil-spaced’ mean anyway?
Instead of spacing
the elements out with air gaps like most refractors, oiled lenses fill the space
with, well… oil: not just any oil, but one with a chosen refractive index to
match the glass. One advantage is that the inner surfaces don’t have to be as perfectly
polished – oil fills scratches – but there are others. Moisture can’t get into
the gaps and cause mould and fungus or deterioration of the glass. Some believe
oil-spaced objectives cool faster as one mass rather than three: good for quick
looks but also when temperatures are falling fast.
But oil
spaced designs can’t use the air-gaps like an extra element to help with
correction and the optical surfaces have to match so can’t be aspherised. So oil-spaced lenses are typically less well
corrected. And there is the possibility of leaks. Some even claim that oiled objectives
should be stored flat to settle into perfect alignment.
Which is
better overall, air-spaced or oil? I have had great experiences with both, so I
honestly don’t know. Does it affect the user experience, reliability? TEC have
been making oiled lenses for a long time so my guess is no.
TEC ‘rigorously
test’ during production, including with an interferometer. Optical quality
should be very high, as you’d expect. Like AP, but unlike LZOS, you don’t get a
test certificate though.
All optical surfaces
are broadband multi-coated.
Collimation
is fixed at the factory.
Tube
The tube is in lightweight aluminium with
a sliding dew-shield. It’s nicely finished in light cream textured powder coat that
resembles a modern Astro-Physics. Internally, there are several knife-edge
baffles to kill stray light (though not the fancy multiple baffles you get with
an AP).
With the dew shield retracted, the OTA
is 840mm long, 150mm diameter and weighs 8.2 Kg. That’s just a little larger
than a Takahashi TSA-120 (an F7.5 120mm triplet) and about 1.5Kg heavier. It’s
a light and compact scope for the aperture.
Focuser
Some early 140s
may have had a TEC focuser, but most ship with the 3.5” FTF3545 Starlight
Instruments Feather Touch that I know well because I owned one for 15 years
attached to a TMB 175!
The FTF3545 is
a great focuser – made in hard stainless, with a 3.5” diameter/4.5” travel drawtube
that features a wide, low-profile rack with ultra-fine teeth, a 9:1 fine focus
knob and an engraved millimetre scale.
The focuser
attaches to the tube via a capstan-wheel assembly that allows you to rotate the
whole focuser when loosened, either to change the camera angle when imaging or
the eyepiece position for visual.
In my
experience the FTF3545, Starlight’s largest focuser, is super-stable under
heavy loads and rarely needs the tension screw to avoid racking out. Precision
is excellent with minimal image shift. The only downside is that loosening the
capstan wheel to rotate the focuser body, though very secure and convenient, does
shift the image a bit at higher powers.
The 140FL’s FT
is customised with an inset TEC badge, but otherwise seems standard.
Mounting
At Kitt Peak,
the 140ED was piggy-backed on a Paramount atop a 16” RCOS in a roll-off
observatory.
At Lowell, the 140FL is mounted on a
new AP1100 mount complete with the latest control box that permits external wireless
control (from an iPad in this case). It is located in the Giovale
Deck observatory, alongside a range of other larger scopes.
At under 10 Kg all-in, the 140FL should
mount on any medium sized mount, perhaps just about on something as light as a
Vixen SX2 or an HEQ5.
TEC APO140FL on an Astro Physics AP1100
mount.
Accessories
TEC offer a
range of accessories, including a case and the lightweight CNC rings you see in
the photos. All are optional extras – something to factor in when considering
the price.
In
Use – Astrophotography
I haven’t had
the opportunity to try imaging with the TEC140. I’ll update this review if I
do. It has a good reputation for imaging, with pinpoint bloat-free stars across
a wide field.
In
Use – Observing the Night Sky
General
Observing Notes
The notes
below derive mainly from two extended viewing sessions at different times and
places. The deep sky views were had with an APO140ED at Kitt Peak under very
dark, clear and stable skies. The planetary views were with a recent APO140FL
at Lowell Observatory under hazy skies but with good to excellent seeing and I
have used the Lowell 140FL on other objects in the past.
On the night I did most of my viewing
with the 140FL, hardly anyone was about due to an approaching snow storm so I
got loads of eyepiece time. Tellingly, I thought, the other scopes stayed
parked.
All the
viewing at both locations was through Tele Vue eyepieces: low power Naglers and
Panoptics at Kitt Peak, higher power Delos at Lowell.
Cool
Down
Both scopes
were stored in unheated observatories, but kept up with falling temperatures well
during both sessions.
Star
Test
The star
test on the 140FL was excellent; I didn’t get to test the 140ED.
Mars
The final
object viewed was Mars, with a 4.5mm Tele Vue Delos giving 218x.
In steady moments,
the 140FL gave a very crisp view of the slightly gibbous planet, 12.9” across a
month after opposition, showing some albedo detail in north and south: the dark
stripe of Mare Cimmerium and Sirenum
in the south; another dark strip of Mare Boreum in
the far north, perhaps a trace of bright limb cloud.
Focusing in
and out there was no red blur visible at all: out of focus, the blur colour was
identical to in-focus: just the pale orange of the planet itself. This ranks the
140FL with the finest apochromats (the LZOS 115/805 – also
an F7 triplet, albeit with an ED centre element - gives a trace of red blur out
of focus, for example).
Jupiter
My viewing
session at Lowell started at dusk on Jupiter at 123x with an 8mm TV Delos
eyepiece. It was a good view and I noted that the Delos suited the 140FL
especially well – sharp and comfortable with lots of eye relief and no
blackouts, but seeing was unstable at first and so detail limited.
Later, they
set the 140FL back on Jupiter in much better seeing after dark and upped the
power to 218x with the 4.5mm Delos.
Now a lot of
cloud belt detail was visible on the 37.8” diameter disk, the image very sharp.
I noted lots of NEB and SEB features: little knots and changes in colour, density
and thickness. The grey polar hood really stood out with good contrast, showing
hints of fine banding. Other belts appeared in moments of extra steadiness.
The four Galilean
moons were visible at once in the 0.3° true field at 218x: proper little disks of
varying brightness and colour, with Callisto at the very edge showing off the TEC’s
flat and well-corrected field.
Saturn
Saturn was small and low and only visible at dusk. Still, it was a good
view that made the best of the conditions, with the rings and shadow, polar
hood and a hint of the Cassini Division clearly visible along with its pinkish
hue unsullied by false colour.
Deep
Sky
The 140ED
gave some wonderful deep-sky views in very dark and still conditions at Kitt Peak.
I noted spectacular
low-powered views of open clusters M41 and M37: sprays of fine stars.
Mag. 5.3
orange giant Eta-Cancri really showed off its natural colour as a sparklingly brilliant
pinpoint in-focus at moderate power, throwing all the light into its tiny Airy
disk – a sure sign of good optical figure.
Globular
clusters M79 and NGC 2419 looked great and were starting to resolve in their
outer regions.
Galaxy M81
in Bode’s Nebula really surprised by revealing its
spiral arms under the dark conditions and with long dark-adapted vision in the
observatory.
The 140ED
easily split Castor, even at quite low power.
Summary
The TEC140 is
typical of the finest highly-evolved apochromats: surprisingly
compact, virtually perfect optically and mechanically.
The objective
is of very high quality and the recent fluorite version (the 140FL) produced no
false colour under any circumstances visually, gave hyper-sharp planetary views.
Meanwhile, its high-power view of Mars suggested that it is very well-corrected
even into the red (APOs often aren’t and produce a deep red blur).
The 140 isn’t
just a planetary specialist. The aperture is bigger than most compact
apochromats and so gave more involved deep sky views under the dark skies at
Kitt Peak, including the spiral arms of M81 which I’d never seen in an amateur
scope.
If the optics
are great, so is the other end of the 140, with the 3.5” Feather Touch one of
the finest available: precise and stable, even under heavy loads and with lots
of travel.
Finally,
build quality looked really good too. The only downsides might be the usual
ones of price and availability: the 140FL has a long waiting list and the price
is quite high, a little higher than Takahashi, though
comparable with AP and LZOS.
The TEC140FL is a wonderful premium refractor,
with superb optics and a larger than usual aperture for its compact size to do
everything well.
