Test Takahashi TOA130S

After about four years of use, I’m writing my thoughts on one of the highest-performing optics on the market: the Takahashi Ortho Apochromatic TOA-130S refractor in the version with a 2.7-inch focuser.

Historical introduction

The new direction of Chinese telescope manufacturing has influenced the market’s development by introducing new, very competitively priced offerings. In this new industry scenario, Takahashi Seisakusho Ltd. has been able to respond well by relaunching its range with excellent apochromats, holding its own both against Chinese production and against well-known brands.

The Japanese company, founded by Mr. Kitaro Takahashi in Tokyo in 1932, began its activity producing valves for submarines; later, after the war, it started developing optical instruments and in 1967 it switched to telescope production. In 1970, it introduced Magnesium Fluoride (MgF2) for anti-reflection coatings and Calcium Fluoride (fluorite, CaF2) for optics. In 1998, the Kyoto Protocol banned fluorocarbons, not fluorite, but during crystal processing fluorocarbons are released and inhaled by workers. Moreover, fluorite is extremely prone to scratches and sensitive to humidity (hygroscopic) and to atmospheric chemical agents. Therefore, Takahashi began replacing the fluorite in FS apochromats with more eco-friendly and less delicate FPL-53 lenses, relying on Canon’s Research and Development division. Among some amateur astronomers there is a suspicion that the move from fluorite to ED glass is due only to economic reasons and not to compliance with the Kyoto Protocol. In fact, the switch from fluorite to FPL-53 made it possible to reduce processing costs because fluorite crystals are much more fragile and easily damaged during machining. Just suspicions? I don’t know, but it is true that older production lines still keep Fluorite (e.g. Sky90, 2009). It has always been known among amateur astronomers that ED glass ensured lower contrast than fluorite, but the superb optics of recent production, such as those of the FSQ106 ED Petzval (second series), have made many enthusiasts think again.

Technical specifications

In 2003 Takahashi introduced new ortho-apochromatic triplets with ED lenses (S-FPL53), replacing the excellent FS-128 f/8 fluorite apochromat with the TOA-130 f/7.7; in 2005 it replaced the FS-152 f/8 with the TOA-150 f/7.3. In the case of the TOA-130 the triplet consists of an S-FPL 53 element placed between two BS7 ones. The stated aim of brothers Kiichiro and Eishiro Takahashi is to produce instruments that set the benchmark for correction of chromatic and spherical aberrations. The Japanese technicians defined these innovative optics as “orthoscopic-apochromatic” (the acronym TOA reads: Triplet Orthoscopic Apochromat); let’s see what it means: “Orthoscopic” is a Greek term meaning "correct vision", i.e. optics free of significant geometric aberrations. “Apochromatic”, according to Abbe’s definition, indicates an objective able to bring to the same point at least the rays of three wavelengths (red, green and blue) and is corrected for spherical aberration and coma for at least two of the three wavelengths. What matters is bringing the focus of red and blue as close as possible to that of green to minimize secondary spectrum, so an apochromat is free of false color. Compared with the previous FS and FCT apochromatic systems (the ones with polluting production under the Kyoto Protocol, so to speak), the TOA-130 can reduce the deviation from green to blue by 1/3. This new optic therefore features a new three-lens optical system, with high refractive index, able to minimize geometric aberrations and spherochromatism. The graphs supplied by Takahashi show that in this instrument spherical aberration is corrected from the G-line wavelength (blue at 436nm) to the C-line (H-alpha at 656nm) with a peak-to-peak tolerance of +/-0.01mm, so the whole visible spectrum is in focus on the same plane. The purple halo of chromatic aberration vanishes and the faint blue residue around bright stars at high magnifications disappears, benefiting shots with digital SLRs, which are particularly sensitive in blue. In addition, the excellent correction also extends into infrared and ultraviolet, benefiting CCD imaging; in fact, over the extended range from 400nm to 900nm the correction stays within +/-0.2mm. However, the direct competitor Astro Physics Gran Turismo EDF 130 f/6.3 is even more capable thanks to a +/- 0.006% tolerance from 430nm (G line) to 706nm (R line).

Takahashi also states that the Strehl Ratio of the TOA-130 amounts to 0.992 and the correction is Lambda/12. For those who like comparisons, Pentax claims that apo refractors of the SDP series have a Strehl Ratio ranging from 0.96 to 0.97. Youri Petrunin produces his TEC140 f/7 with a correction of 0.99, while Roland Christen builds his Astro Physics with a value of 0.984 and a correction close to Lambda/30. The values mentioned are all of the very highest level, placing the instruments in a sort of Olympus of amateur telescopes. A telescope’s Strehl Ratio indicates the percentage of the light of a stellar image that falls inside the Airy disk, and the maximum theoretical value possible (100%) corresponds to 1. For the optics to be corrected for aberrations, one must ensure that the spot caused by diffraction (Airy disk) exceeds that caused by aberrations; to meet this criterion the maximum wavefront error must not exceed Lambda/4, otherwise the aberration becomes visible and compromises the image. To have a benchmark with the legendary Zeiss APQ130 apochromat, Zeiss states that its lenses are figured to Lambda/29. However, one must also consider that it is almost impossible for an amateur astronomer, even with 11/10 eyesight, to catch the difference between an instrument corrected to Lambda/12 and one corrected to Lambda/30; I do think, instead, that one can grasp the differences between instruments that have the same optical purity, but with different configurations (oil-spaced triplets vs air-spaced triplets vs quadruplets). From field comparisons with the instruments mentioned, I was able to verify the superiority of the TOA-130 in geometric and chromatic correction compared to the TEC 140, at the expense of slightly less sharpness at the center. The TEC seems a bit sharper at visual wavelengths (520-560nm), while the TOA seems to have higher sharpness on average across the whole spectrum.  Based on these characteristics, I consider the TEC superior for visual use, while the TOA for CCD imaging. Compared to the Astro Physics EDFS 130 f/6, the only difference I noticed is a calmer view in the latter. The declared Strehl Ratio data are the theoretical ones stated by the various manufacturers; in practice it is very rare that they are the real ones, even if they come very close—each optic, even of the same model, is different from the other. I would be very curious to compare the TOA with the Zeiss APQ130, AP155 apochromats and the Nikon 100ED f/12. See the point-like stars (taken from the Skypoint.it site):

Two versions of the TOA-130 are produced: the F version with a wide 4-inch focuser and a usable image circle of 92mm, and the S version with a 2.7-inch focuser, a 40mm image circle and a 2.3 field, which allows prime-focus photography on 35mm. I preferred the S version because I have no need for photographic work in the 6x7 format.

I received the tube, supplied only with the eyepiece/accessory adapter, in a double cardboard package. Once opened, the first thing that struck me was the beauty and elegance of the white paintwork; the tube has a classic design and excellent looks, but is rather bulky; it seems less suited to transport than the Pentax 125 SDP and the Astro Physics 130 EDFS, which are also characterized by a rougher paint finish and more scratch-resistant. From the very first visual contact, the special care in construction immediately stood out: tube length 1015mm with focuser retracted and without accessories, diameter 156mm, weight 10.5Kg (the F version weighs 11.4Kg), 179mm-wide dew shield that extends by 160mm. The tube mass is remarkable; consider that it weighs about 3Kg more than the predecessor FS128 and 2Kg more than the average of competitors. This is an advantage to avoid tube flexure. The dimensions are also imposing, but are justified by the long 1000mm focal length. The care in construction is obsessive in order to avoid the dispersion of internal thermal currents, fast acclimation and the maintaining of collimation. Such bulk puts my SkyWatcher Eq6 Pro mount to a hard test, especially during photographic shots and focusing at high magnifications. To reduce vibrations I replaced the counterweight bar with a thick 3.1cm one (the original is only 1.8cm thick) and I fitted a dovetail rail wider than the original Losmandy type and 40 cm long (LBAstro). Now the tube with the handmade rings and the plate weighs 13Kg. I still believe that my Eq6 Pro (grease replaced and modified with SKF bearings, 31mm counterweight bar and with reinforced Geoptik tripod) is still not sufficient for CCD imaging. I recommend higher-class mounts such as those in the G41 class, Bellincioni Omega, RM-300, 1000HPS... The front lens is protected by a push-on cap and by the nice cell; the latter seats the optics with as many as 18 screws for collimation. Personally I would have preferred a screw-in cap with a central hole to stop down to 10cm. The particular tube design of the cell ensures excellent protection of the optical-mechanical system from jolts that may occur during transport and allows the optics to quickly reach thermal equilibrium as the outside temperature changes. I have never had problems with condensation and fogging. The inside of the tube is perfectly matted and blackened with sharp-edged baffles alternating with numerous micro-baffles. The three lenses are dark, air-spaced and divided into three groups; between the two crown elements an ED lens (S-FPL53) is placed, as in the Astro Physics 130 EDFS, whose lenses are oil-spaced. The triplet has as many as six multi-coatings to ensure the highest possible contrast. The stated light loss is only 0.5% on each coated surface, versus almost 2% on each surface of oil-spaced systems. In addition, maintenance is lower than that required by the latter, since there is no oil that could leak out or become cloudy over time. Looking at the objective from the outside, one notices the uniformity in transparency and the multi-coatings appear very efficient. The outer lens appears free of bubbles, streaks and Newton's rings.

The focuser is a 2.7" rack-and-pinion unit and allows smooth, backlash-free focusing but, unfortunately, it lacks the micrometric marks typical of the Pentax SDP. It has a total travel of 7cm and seems insensitive to thermal expansion. The 50.8mm eyepiece holder screws directly onto the focuser and is supplied with a 31.8mm adapter with a self-centering collar that keeps any accessory perfectly centered, preventing it from being scratched, as happens with screw systems. Unfortunately the self-centering collar is present only in the 31.8mm adapter and not in the 50.8mm one. The two large aluminum knobs for focus adjustment are easy to use even with gloves; an oversized central screw allows you to lock and keep the focuser in the correct focus position. The focuser is well made; however I would have expected a more refined system like the dual-speed reduction ones with a 1:10 ratio that, for example, TEC offers as standard. Takahashi provides a reduction system “Micro Edge Focuser” as an accessory, but from a field test it seemed too light and with loose play. For those who want to use the TOA-130 for astrophotography I suggest fitting the focuser with a Feather Touch retrofit system (about 230 Euro, 2012), or with a RoboFocus controllable via PC. A useful photographic and visual accessory is the “Camera Angle Adjuster”, i.e. the camera rotator, which screws onto the focuser before the eyepiece holder; it allows the camera to be rotated along the optical axis by 360° without losing the correct focus position and orthogonality. This accessory is very useful also with the binoviewer; however it disappointed me both because it is rather stiff to rotate and because it shows very uneven resistance during rotation. After taking it apart I discovered that the problem was due to a teflon friction ring that was not perfectly spherical; to restore proper smoothness it was re-ground by a friend of mine (Mauro Meco of Fi). In August 2012 I replaced the Takahashi CAA with the same model from the Italian company LB Astro (by Lorenzi and Bernadi). The latter is smoother and sturdier. Excluding the Japanese rotator, it seems everything was made with meticulous care and that the tube assembly was built without compromises, both in the key components and in the finishes. Other useful accessories are the focal reducer (2 lenses) that brings the focal length to 750mm f/5.8 and extends the photographic field up to 3.8° with a 52mm image circle (with dedicated rings this value can vary), the field flattener that slightly reduces the focal length bringing it to 980mm, and the Extender TOA-1.6X (5 lenses in 3 groups) that brings the focal length to 1600mm f/12.3 with a photographic field of 1.4°. This last accessory particularly impressed me for its high quality: it always provided images so crisp and clear that it felt like observing without the multiplier. Takahashi accessories are countless and allow every kind of visual and photographic application while always guaranteeing the highest quality. Fortunately there are system charts that show the placement of each accessory. However, when choosing I advise paying close attention to the nomenclature to avoid buying wrong rings and to follow only the TK codes; for example the company uses the same name: CA-35, both for a 50.8mm photo-visual adapter and for a ring that allows you to reach focus when using the focal reducer. In addition, Takahashi has developed ED-glass eyepieces optimized for this optic: LE-ED 2.8mm, the flat field LE-50mm and the Taka UW 90 (the latter are aplanatic and must be paired with the flattener).

Field test

The features I saw convinced me to buy a TOA-130S to replace my old Vixen Newtonian (see Nuovo Orione, no.198, November 2008). It is logical at this point to expect from this instrument performance and optical output close to perfection. After one year of use, let’s see whether the telescope has lived up to expectations.

Not having the chance to carry out an analysis with an interferometer, I settled for the classic visual inspection of the Airy disk. After letting the optics acclimate, I performed the star test on the diffraction image of Arcturus, examining it with the focuser in the intra-focal, focus and extra-focal positions. The optics proved to be perfectly collimated and, as expected, the intra/extra images appeared identical and perfectly spherical. I perceived the regularity and symmetry of the rings, a sign of the absence of zonal errors. I detected none of these faults: spherical aberration, zonal errors, field curvature, chromatic aberration, astigmatism, stresses, coma and roughness. The Airy disk was uniform and without halos. Even the bright limb of the Moon was free of false color. During the test there was wind and the windward side of the tube was colder than the leeward side, so I expected internal convective currents; nevertheless I did not notice the typical heat plume that distorts the Airy disk. This indicates excellent tube baffling. Long-exposure photos with a "full frame" SLR showed loss of pinpoint stars at the edges and field curvature. For this application it is necessary to use the dedicated field flattener.

In this shot of M42 you can clearly see the distorted field on the left edge and the loss of pinpoint stars. To limit the problem you need to use a field flattener. The shot was taken with a Canon Eos 5D MKII at 500 ISO with an exposure time of 30 seconds. If I had used an APS-C sensor, the defect would not have shown up (download the photo to see the defect better).

Airy disk of the Toa 130 by Stefano Arrigoni

Test carried out with CCD Inspector by Stefano Arrigoni

The images obtained with CCD Inspector by Stefano Arrigoni show that his TOA has a curvature contained within 5.9%

Sky observation

The view of star clusters, showing pinpoint stars right to the edge, is enchanting and breathtaking. The perception of colors is a unique experience. The black sky seems detached from the shining stars like pinheads. The view of M13 is gripping: you can resolve the halo and the swarming of stars extends to the edge of the field, almost as if to envelop the observer! A dark "V" in the core is barely perceived. M3 with the Pentax XW10 (100x) is truly a gem; I couldn’t resolve the whole core, yet it strikes you by how detached and contrasty it is. The Double Cluster in Perseus with the Ethos 13 and the Pentax XW20 (50x) takes your breath away; you see pockets of pitch-black sky linking with skeins of tiny, colored, ultra-fine stars; there are stars of every color and the almost three-dimensional view surpasses a previous observation with the Miyauchi 20x100ED. Even with a 25mm Erfle, of unknown brand, I had a breathtaking view. M51 at 100x appears very bright and clearly attached to NGC5194; the field is rich in tiny stars. M31 at 50x spills out of the eyepiece field and the huge amount of detail is staggering. The dazzling Epsilon Bootis “Pulcherrima” was easily split with a Pentax XW5 (200X), despite the seeing not really favorable. The colors of the components were particularly vivid. Unfortunately I had no chance to test the optics on more difficult doubles, whose separation approaches the resolving power (0.89"), such as ADS1538 Cet (0.94") and STF 1338 (0.92") in Lynx. Albireo was thrilling, as were Alcor and Mizar. In all observations the stars appeared extremely fine, right to the edge of the field, thanks also to the excellent eyepieces, and in some cases it felt like observing through the porthole of a spacecraft. 

The TOA is a perfect astrograph, in the figure you can see the different available fields:

1) Full-frame DSLR with focal reducer: 750mm, f/5.8

2) Full-frame DSLR at prime focus: 1000mm, f/7.7

3) APS-C DSLR with focal reducer

4) APS-C DSLR at prime focus

5) Kaf 400 CCD at prime focus

I observed Jupiter with a Pentax XW5 +1.6X (320x) and a Vixen Or 4mm (250x): the belts were clearly visible, some detail could be seen within the Great Red Spot and in the nearby structures; I easily spotted the bright ovals between the STB(S) and SSTB bands, and I also perceived a few small ovals in the SSTB. With a Pentax XW10+1.6X Jupiter’s disk appeared white, with no color loss due to wavelengths not in focus. I had the impression of observing a three-dimensional globe and not just a two-dimensional one against the sky background. Observing Saturn, with a Pentax XW5 and Extender-1.6x (320x), I appreciated the optics’ perfect achromaticity; the planet’s disk looked carved against a velvet-black sky background. Saturn too, as with Jupiter, seemed to stand out from the sky background!

On the lunar surface I focused on hunting down difficult details. I lingered, with satisfaction, on observing the tiny craters A and B along the Hypatia rille. The view of the terminator descending near Arzachele and along Thebit A and Thebit L was thrilling. The details inside the fractured floor of Posidnius appeared well contrasted, and the shadows cast by Alpes Vallis and Mons Piton were very sharp and seemed thrown by Gothic spires. The images were very crisp; in the past I had the same feelings observing with the predecessor FS128 and Radian eyepieces. With an AP 130 EDFS f/6 (with Radian) I saw the same amount of detail as with the Toa-130; with the EDFS the images seemed more soft and calm, while with the Takahashi they appeared more contrasted. The two instruments delivered very similar images and at the same level, but with different “plasticity”. Unfortunately I could not fully exploit the optics’ potential in high resolution because I didn’t have the chance to use high-quality orthoscopics such as the Zeiss Abbe.

2019 update: in deep-sky I’m getting a lot of satisfaction with the Televue Ethos 10 and the ES100 14 and 20. I also tried a Televue Ethos 21 whose performance is almost indistinguishable in the center compared to the ES 20; the Televue pulls ahead from 2/3 of the field toward the edges. For ultra-wide fields I use a Nagler 31.

2020 update: With an ES100 5.5 I obtained a very relaxed and scenic view of the lunar disk; I replaced this eyepiece with the Ethos 4.7, but I still haven’t perceived any advantage over the ES.

2021 update: with a Toe 2.5 eyepiece the view of the Moon is incredible, probably the best telescope/eyepiece pairing I have ever tried.

I compared the TOA-130 photographically with the Canon EF500 f/4L IS (17 elements in 13 groups) with 2x extender, to see whether the Canon super-tele could be a valid and more practical alternative for photographing events like eclipses and conjunctions. I took many shots of the moon, getting well-made files with the Canon, but not a single good shot with the telescope because of the strong wind that made the telescope tube vibrate. So I decided to continue the test by photographing a farmhouse, because that allowed keeping the tube in a more stable position. The result is clearly in favor of the TOA-130 in terms of resolution, sharpness, vignetting and color vividness. This conclusion was also predictable due to the smaller number of lenses in the telescope.

The farmhouse was placed at the edge of the frame to highlight aberrations and these images are crops of 100% enlargements: both lenses perform excellently, but the Takahashi is superior in sharpness, color rendering and vividness.

Venus transit with Taka 1.6X Multiplier and Canon Eos 5DMKII (photo by the Author)

M106 and NGC4217 (photo by Marco Burali and Marco Mancini, OSS.MTM)

NGC 7023 from Colle del Nivolet, Toa 130 with reducer at f/5.8 on Atlux mount, SBIG ST4 autoguiding Canon Eos 50D with Baader filter, 800Iso, 105-minute exposure (photo S.Arrigoni)

NGC6559 with Canon EOS 30D with Baader filter, 800 ISO, 3h exposure (photo S.Arrigoni)

Conclusion

The optical and mechanical quality of the TOA-130 ranks among the very best on the market. It features exceptional sharpness, and is aimed at advanced amateurs who want to try their hand at planetary and deep-sky observing, provided they use high-quality eyepieces. It always delivers perfect images. It is also fully usable in the field of astronomical photography, both with DSLRs and with modern CCDs. For astrophotographers I recommend also factoring in the purchase of accessories such as the field flattener, the focal reducer and a dual-speed focusing system. In short, this wonderful apochromat could be the end point for many demanding astrophotographers who, between one shot and the next, can also enjoy deep-sky and planetary observing without missing larger apertures. Of course with a Dobsonian galaxies are brighter, but it certainly does not disappoint. 

PROS

• top optical quality
• low sensitivity to turbulence
• build quality and sturdiness
• color transmission
• absence of aberrations and in particular spherochromatism

CONS

• weight and bulk
• delicacy of the paint finish
• faulty field rotator (my sample)
• focuser not up to the task

Post Scriptum

The comparisons made with the Tec 140 and AstroPhysics EDFS 130 instruments took place sporadically during various meetings and star parties.