When Takahashi discontinued the FS series,
which spanned 60-152mm apertures, they effectively gave up on the idea of
having a single scaled design. For the smaller apertures, Tak’ continued
with fluorite doublets, retaining the FS-60 and re-introducing the FC-76. At
the upper end they introduced the TOA-130 and TOA-150, triplets with a very
large air space and two ED elements that are heavy but give the best colour
correction of any APO. For the middling apertures they deployed conventional F8
ED triplets - the TSA-120 and the TSA-102 on review here.
Very recently, the TSA-102 has been
discontinued, replaced in turn by a brace of 100mm fluorite doublets, but
that’s a shame because the TSA-102 turned out to be a very different
scope from the old FS-102 (and the newer FC-100D too) with different strengths
and weaknesses. As we will see, if you can find a good used one it’s
still a great buy.
At A
Glance
|
Telescope |
TSA-102S |
|
Aperture |
102mm |
|
Focal Length |
816mm |
|
Focal Ratio |
F8 |
|
Length |
~ 625mm (25”) minus extensions |
|
Weight |
5.4 Kg |
Data from Takahashi/Me.
What’s
in the Box?
The TSA-102 came in a typical Takahashi double box:
Design
and Build
Like other Tak’ refractors, the TSA-102 was
available in fixed (TSA-102N) and sliding (TSA-102S) dew-shield versions
– the fixed version longer but lighter. The cream tube and green enamel
livery was the same, but the dewshield had green writing in place of the
traditional Takahashi blue. Otherwise, The TSA refractors are typical
Takahashis, plain and simple but beautifully made.
The TSA-102 is long gone, but the larger TSA-120 is
still on sale as I write in late 2024. Perhaps that’s because it’s
not that much larger or heavier:
Optics
The acronym TSA stands for Takahashi Super
Apochromat and is significant. A ‘Super APO’ is supposed to be
essentially free from chromatic aberration. A ‘Super APO’ should
also be free from spherochromatism - maintaining a high Strehl across the full
visible spectrum. As we will see, in these respects the TSA label is a
statement of fact.
The TSA-102’s lens is an air-spaced
triplet made in Japan by Canon/Optron. The quality of both the cell and the
glass is of the very highest, but the design is quite conventional, unlike the
larger 130 and 150 tak’ APOs which use a very
large air gap and twin ED elements to allow even further control of
aberrations. Why doesn’t the TSA get this design? Quite simply because at
this aperture it is unnecessary: the job can be done with a conventional F8 (816mm
in this case) ED triplet that uses a centre element made of top quality S-FPL53
glass sandwiched between two crowns with small air spaces between. It’s
essentially the same kind of design that LZOS use for their own outstanding
apochromats.
Air-spaced triplets like this one are
generally harder to make (because all glass surfaces must be finely polished) and
generally perform better than the oil-spaced variety (apologies to AP, TEC et
al), but may take longer to cool. Also, the air spaces ‘breathe’ so
there is more chance of internal fogging or mould.
Takahashi don’t supply a certificate of
optical quality (unlike APM/LZOS), but nonetheless bench tests indicate Strehls of 98% for production TSAs – a result every
bit as good as the LZOS lens and better than the modal quality of the old FS
series. As you would expect, Takahashi use the finest coatings (on every
surface – I checked) and that cell is a work of art that makes for very
rapid cooling.
So how does the ED triplet TSA-102 compare to
the model it replaced, the fluorite doublet FS-102? A comparison of the two
designs, using Tak’s own data is interesting. The poly-Strehl values tell
their own tale. For one thing we can see the effect of the triplet most in the
violet: The FS-102 falls off a cliff below about 450nm, whereas the TSA-102
still manages a decent showing at 420nm which is at the limits of the visible.
This is a clear benefit to imagers. At the other extreme – the far red
– Strehl performance is very similar: neither suffers the spherical
aberration in the red you often get with faster ED doublets.
The other telling difference is the wavelength
for which the theoretical performance is highest. For the FS-102 it’s in
the yellow; for the TSA-102 it has been pushed to higher wavelengths for
reduced violet bloat in images.
In terms of spot sizes, we get some more
evidence that the TSA has been designed with the imager in mind. Its spot sizes
are all smaller (better) than those of the FS-102 in the shorter wavelengths
… until you get past green. But for yellow and red, the FS-102 actually
manages consistently tighter spots, tending to confirm my experience that the
FS series are great for Mars.
Overall,
it’s clear that the TSA-102 will be the imager’s friend, but for
visual the FS-102 runs it surprisingly close for a doublet, on paper at least.
Spot diagrams suggest TSA-102 is better for
imaging, FS-102 (perhaps) for Mars!
Tube
The TSA-102 tube is typical Takahashi –
rolled aluminium coated in white enamel with a cast lens ring in knobbly green
powder coat. Internally, the tube has a number of knife-edge baffles and is
flattened with super-matt black camera paint.
Simplicity is the theme: Takahashi Zen. Build
quality is palpably superb. The focuser screws in and is locked with a tiny
grub-screw: no push-fit and protruding screws here. Likewise, the ample
dew-shield threads onto the sliding lens ring which moves smoothly and clicks
into place.
The old FS-series cast ‘manhole
cover’ cap is replaced with a conventional pressed-tin item. The FS
manhole cover was complete overkill, but I loved it.
The fixed dew-shield TSA-102N is cheaper and
(400g) lighter, but almost 19cm longer than the TSA-102S (reviewed here) with
its dew-shield retracted. To make it shorter, the TSA-102 is designed to be
used with an extension tube (supplied), but this is only really needed for
straight-through viewing or DSLR imaging.
Remove the extension and unscrew the eyepiece
holder from the focuser drawtube, slide the dew-shield fully back and you end
up with an OTA that is barely 25” long. That’s the same as a Tele
Vue NP-101 - very compact for an F.L. of 816mm. But, unfortunately, it’s
not definitively carry-on portable.
Again, comparisons with the sliding dew-shield
version of the FS-102 are inevitable – the tube and focuser are very
similar, but despite being exactly the same focal length, the FS-102 may be
slightly shorter (see photos).
For comparison: sliding dew-shield FS-102 has
a very similar tube and focuser to the TSA-102 (the dual-speed focuser pinion
is an after-market upgrade).
Focuser
The TSA-102 uses Takahashi’s medium
2.7” focuser, much like that fitted to the defunct FS and FC series. The
focuser body is cast, not CNC, and painted the usual delicious Tak’ lime
green; the knobs are the equally delectable standard silver metal items (no
plastic imitations here, unlike the FS-60 and FS-78).
The focuser is a rack-and-pinion design, but
with a very wide rack and cross-cut teeth for smoothness and stability. The
visual back uses threads onto which you can fit various adapters including
2” and 1.25” eyepiece holders, T-rings, camera rotator, reducer,
etc.
Takahashi are apparently very proud of their
focuser and with this example it’s not hard to see why. It is a superb
unit: beautifully smooth and precise with
virtually no image shift and capable of handling heavy eyepieces and cameras
with ease. The big silver knob on top locks the focuser and it too works
perfectly, with no image shift.
No, it isn’t a Feathertouch
and no it doesn’t have a microfocuser (they
make one as an add-on), but for visual use at F8 you don’t need one
– the single speed is so accurate getting critical focus is easy.
I have
tested other Tak’ focusers that have significant image shift, but I
suspect this is due to wear from carrying heavy CCD cameras. This
focuser doesn’t suffer significantly from the problem and neither did my
(owned from new) FS-128. Best to try before buying used, though.
Mounting
The TSA uses the typical Takahashi cast
clam-shell tube ring with two 35mm spaced M8 bolt holes. Again, it’s a
beautifully made thing with thick green felt, double hinges and a heavy,
thickly chromed lock knob. Do I sound like a Takahashi fetishist?
The clamshell attaches directly to the top of
any Takahashi mount. For other mounts things are a bit trickier, but it’s
easy enough to find Vixen dovetail bars from third party suppliers with the
correct holes and threads. If you get stuck, Takahashi make a dovetail bar for
one of their dovetails that also works in a Vixen fit – ask your dealer.
One small issue with traditional Takahashi
castings, rather than CNC, is that orthogonality won’t be sufficient for
critical alignment of a GOTO mount. In particular, those M8 holes in the
clamshell just allow too much free play.
The TSA-102 is quite
heavy (due to its triplet lens). Add ring, finder, diagonal and eyepiece and
the basic weight of 5.4kg soon creeps beyond the ~7Kg limit of most small
German mounts, so you’ll need a
medium sized mount: an EQ5 will struggle. The Takahashi P2Z shown here coped,
but was straining a bit. A Tak’ EM-11 will be fine, an EM-200
super-steady.
TSA-102 on P2Z mount.
Accessories
Accessories include an extender, flattener,
reducers, camera-angle adjuster (also great for visual use, by the way), wide
T-mounts and more. Two reducers are available: F6 and the much more expensive
F5.6 TOA-35 reducer.
Another obvious accessory decision is a finder
- should you choose the 7x50 or the 6x30? It’s a tough choice. The 6x30
is a minor legend and with reason: it is small, light and has a wide bright
sharp field with masses of eye relief and a smooth helical focuser at the
eyepiece end. If weight or cost is an issue (and a fully fitted-up TSA-102 is
at the top end of the weight capacity for a small mount, as I’ve said),
then you’d go for the 6x30. Its knurled silver focus ring also looks a great
match for the focuser knobs.
The 7x50 finder is a much larger, heavier and
more costly item. What’s more it doesn’t have as much eye relief.
However, it is ‘probably’ the best 7x50 finder on the market with
an excellent reticle that leaves a small gap for the
target, rather than obscuring it in the cross-hairs like most do. You can
thread in an illuminator too, which makes it even easier to use.
In Use
– Daytime
The easiest way to push a refractor to reveal
its true colours is to turn it on a high-contrast subject during the day: tree
branches against a bright sky are perfect. Now ramp up the magnification to
over 100x and most refractors, even apochromats, will show some colour fringing
either side of those branches. Even if you don’t see any colour in focus,
try racking in and out of focus and you’ll see it. But not with the TSA.
It shares the distinction, with the APM/LZOS 100/8, of being one of the few refractors
I have tested to show absolutely no colour in this test, in or out of focus.
Bench tests have confirmed this excellence and match Takahashi’s own
published data on the lens.
In Use
– Astrophotography
Perhaps surprisingly, the TSA-102 has been the tool
of choice for some of the best imagers, usually equipped with one of the
reducer or flatteners options. I didn’t have a chance to try it, but
suspect violet bloat would be much less of a problem than it often is with
doublets (and even Petzvals).
The TSA-102 certainly takes sharp, contrasty and
detailed snaps of the Moon.
In Use
– The Night Sky
General
Observing Notes
For use on the Moon and planets the TSA-102
gives high-power images that are always sharp, high-contrast and absolutely
free from chromatic aberration or stray light bloat.
I have always been a big fan of the old FS
fluorite doublets and it remains true that they have a small theoretical
advantage in terms of contrast. However, in practice the TSA is as good as the
FS-102 and in some ways slightly better (higher optical quality on this example
and even less chromatic aberration on most things).
Cool
Down
The TSA has textbook cool-down
characteristics. Put it out into a frosty night from a warm room and it shows
quite severe spherical aberration for the
first few minutes only – no astigmatism, no pinching. This spherical
aberration fades with the tube currents in the star test for the first thirty
minutes or so of use; after that … perfection.
Overall,
cool-down is impressively fast for a triplet, thanks to the sophisticated cell,
but a doublet still cools a bit faster.
Star
Test
Once cooled for half an hour the star test is
pretty simple to describe: it’s perfect. Really. I can’t see any
difference either side of focus and the zingy rings are perfectly evenly
illuminated and very well defined; the outer ring has no fade-off.
When you see a star test that good, you know
the in-focus views won’t disappoint and that is certainly true of the
TSA-102. In good seeing, an in-focus star reveals a perfect Airy disk with a
perfect faint diffraction ring around it.
In this respect at least, the TSA beats its
FS-102 forbear. The FS-102s I have seen are typically 1/5th to 1/6th
PV with a noticeable trace of spherical aberration (like most premium scopes,
my TMB 175 included, in fact). The TSA is significantly better – I reckon
my example is up at 1/8th wave, again in-line with bench-test
figures I have seen.
Does this extra optical perfection matter?
Probably not. Still, The TSA has the best
optical quality of just about any refractor I have tested.
The
Moon
The Moon is a magnificent sight through a
really good 4” refractor like the TSA-102 - absolutely crisp, all
blinding-white uplands, blacks shadows and grey scale Maria, with no false
colour whatsoever, even focusing through the limb at high power.
Combine the zero CA with minimal stray light
and you can enjoy Lunar mountains picked out in silhouette against the black of
space, or a peak shining out from dense shadow beyond the terminator.
In terms of detail, numerous rilles can be
traced in good seeing and you can play at trying to find the end of Rima Sirsalis. Craterlets and dome fields can be explored in a
way not possible with smaller scopes. By pushing the magnification on a night
of fine seeing (the TSA-102 soaks up high powers), you can investigate those
dark patches in Alphonsus, count craterlets in Plato, glimpse Hadley Rille near
the Apollo 15 landing sight, follow the rays from Tycho out across the
highlands.
Jupiter
Jupiter is a
tough object due its brightness and low contrast, but the TSA-102 gives one of
the finest views of it I’ve seen. With a 5mm Type 6 Nagler or 3-6 Zoom on
the 5mm setting giving around 163x, Jupiter is absolutely crisp and detailed,
all creamy buffs and no false colour. One advantage of the longer focal length
(compared to say an NP-101), is that getting high powers is a bit easier and
you’re less likely to have to invest in specialist eyepieces for planets.
Numerous cloud belts are visible, some with
dark storms, whorls and bifurcations. The GRS and both grey-blue polar hoods
could easily be picked out, with a hint of pinkish-buff colour in the GRS (as
much as you ever get these days). At times of good seeing there was the hint of
more detail to come – banding in the hoods, more dark and light spots in
the belts, the thickening and vortices downstream of the GRS.
At high power, the Galilean satellites are
easily resolved and distinguished based on size and colour.
In
comparison with something like an NP-101 – good though the Tele Vue is -
I do think the extra optical quality of the TSA-102 is noticeable at high
powers on planets in good seeing.
Deep
Sky
Four inches of aperture is small for a deep
sky scope, but the tight point spread function, flat field and inherently high
contrast really help. Star fields and clusters give that brilliantly sparkling
effect, with OB stars dazzlingly luminous against a perfectly black sky (I
promised myself I wouldn’t mention diamonds on velvet ever again). The
double cluster has an almost 3-D appearance with the fainter central stars
seeming recessed from the outer ones; that red star between the clusters is a vivid
colour like a hot coal.
The brighter Messier objects reveal more structure than through many
small scopes and again that visually flat field really helps, so that
you’ll easily pick out the dark lane in Andromeda, see the hour-glass
shape of the Dumbbell Nebula standing out like grey smoke and make out the eye
shape of the Ring Nebula.
At this focal length, wide fields are still
easily possible and the whole Pleiades, Bodes’ pair of nebulae and other
extended objects and clusters easily fit in at lower powers. But the F8 ratio
makes for easier focusing and places less strain on eyepieces, so the TSA-102
is singularly unfussy about the glass you choose to pair it with.
I would expect the F6 reducer to convert the
TSA-102 into a superb imaging machine, but for casual use the field is very
flat to start with. Both curvature and off-axis coma are very well controlled.
With a flat-field eyepiece like an Ethos you get pin-sharp stars to the field
stop.
Summary
All in all, the TSA-102 is worth its premium
price. Why? Because what you get is just perfection: perfect star test, perfect
build quality, a perfect view of every kind of object. This could really be
that buy-it-once-last-a-lifetime only scope.
Even the focuser is as good as any. No,
it’s not a Feathertouch: it has a touch more
image shift and no dual-speed, but it’s arguably got an even nicer,
smoother, more fluid feel. And the threaded visual back is much more flexible
than just a 2” compression ring.
The question of which is the better scope
– the TSA-102 or its FS-102 forebear - is moot. The FS-102 is a tad
lighter and cools more rapidly. It may deliver a very tiny contrast advantage
and may be just a little better at the red end (so particularly for Mars).
However, in other respects the TSA is the better refractor – higher
optical quality on my sample, better suited to imaging.
Just about the only downsides to the TSA-102,
like most 4-inch triplets, are weight and cool-down.
Very highly recommended: with the TSA-102,
Takahashi honed the small triplet apochromat to exquisite perfection.
