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Takahashi TSA-102S Review

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?

Takahashis come in double or triple boxes:

 

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.

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. To be very clear, this kind of triplet is harder to make (because all glass surfaces must be finely polished) and generally performs better than the oil-spaced variety (apologies to AP, TEC et al).

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.

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.

Mounting

The TSA uses the typical Takahashi cast clam-shell tube ring with two 35mm spaced M6 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 M6 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 the only refractor 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 and even less chromatic aberration).

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 under-corrected 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.

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

Perhaps more than any other expensive scope I’ve tested, 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 all other respects the TSA is the better refractor – higher optical quality, better suited to imaging.

Just about the only downside to the TSA-102, like most 4-inch triplets, is its weight. Which brings us to its main competitor. For just a (surprisingly) little extra cost, weight and bulk you can have the TSA-120, which is likely quite a step up (~40% more light gathering, 20% higher resolution). Given that the TSA-102 pushes the limits of a small mount anyway, I might be tempted to opt for the larger model. And, perhaps not coincidentally, it’s the TSA-102 that got discontinued.

Very highly recommended: with the TSA-102, Takahashi honed the small apochromat to exquisite perfection.

Updated by Roger Vine 2018

 

 

 

 

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