TS-Optics 152 mm f/5 ED Rich Field Refractor with 4" RAP Focuser

TS 152 mm f/5 Rich Field Refractor and Comet Seeker

This 2-element ED is a truly extreme telescope for the ultimate in wide-field observing. The stars are needle fine, as only a well corrected refractor can produce. At the same time, the refractor is still easily transportable with a transport length of about 70 cm and 11 kg. A stable alt-azimuth mount or a good equatorial mount like the AVX or the H-EQ5 are recommended as a base. The 2-element ED lens from Japan offers an image up to about 100x without disturbing false color due to the very good chromatic correction. Sharpness is maintained up to about 250x, but we then recommend a filter to reduce chromatic aberrations.

The 2-element objective in a temperature compensated cell:

The optics and the cell are made in Japan. The imaging quality is high and even at the maximum magnification range, the contrast remains hard. The chromatic aberrations are reduced by the ED element made of FCD1 from HOYA.

Astrophotography with the TS 152 mm f/5 ED refractor:

Although the telescope is optimized for large field observation, photography of nebulae and galaxies will also succeed with it. The fast focal ratio of f/5 allows short exposure times. However, a field corrector is absolutely necessary to get sharp stars to the edge. We recommend the TSFLAT25DEL 1.0x corrector, which screws directly into the M63x1 female thread of the focuser. The working distance is 55 mm from the M48 thread.

Technical Information

Teleskop-Service has collected a lot of helpful information about refractors and provided it in English as a PDF file: refractors.pdf

First Light with the TSED152 F5

Tonight was the First Light for the TS 152 mm f/5 ED refractor. Based on my observations today, I rate the quality of the lens as follows:

Ronchitest: perfect! >>> All "fence slats" are completely straight and exactly parallel - even at highest magnification (2 "fence slats").

Startest: Intrafocal: circular, evenly illuminated diffraction slice, in which all Fresnel rings up to the point in the center of the slice are clearly visible and rich in contrast; the Fresnel rings are absolutely concentric; extrafocal: as intrafocal with the only difference that the Fresnel rings are not quite as rich in contrast, but are somewhat washed out; the chromatic aberration is noticeable intra- and extrafocally (e.g., by the fact that the intrafocal slice is not as bright as the Fresnel rings in the center of the slice). The chromatic aberration is noticeable intra- and extrafocally (e.g., the intrafocal diffraction disk is slightly yellowish and surrounded by a violet fringe).

I have already performed a star test on numerous refractors. Only on two other two-lens objectives has the star test shown equally good (but not better) spherical correction, namely a Takahashi FS-128 (f/8.1) and a Zeiss AS 100/1000. Neither a Takahashi FC-76DC (f/7.5) nor a Takahashi FC-100DC (f/7.4) showed "almost identical" intra- and extrafocal diffraction discs as the 152 mm f/5 ED; rather, only 2 Fresnel rings were visible extrafocally with these two Takahashis; the rest of the diffraction disc was featureless (chromatic correction was better with the Takahashis, of course). Even better results (completely identical perfect intra- and extrafocal diffraction discs) were achieved only with two triple-lens full apochromats, namely a Takahashi TSA 120 (f/7.5) and an APM-LZOS 152/1200.

In focus, with the 152 mm f/5 ED, chromatic aberration shows up only with bright stars and higher magnification. In particular, the colors that are not focused accurately (blue-violet and red) are "thrown out" in turbulent air. However, the latter is the case even with two-lens f/7.5 Fluorite apochromats, except that this effect is naturally stronger with the 152 mm f/5 ED. Overall, however, the color correction of the 152 ED is surprisingly good considering the large aperture and the extreme focal ratio.

Stars are reproduced razor sharp by the 152 ED even at higher magnification (217x with 3.5mm Pentax XW). The image "snaps into focus." The quality of the optics is also evident in double stars, which are sharply and clearly separated. Eta Orionis (m = 3.6-4.0 /4.9; d = 1.8") was no problem for the six-incher, of course, despite choppy air. I have no doubt that with good seeing the refractor can accurately separate double stars at the Dawes limit (0.76"). I was surprised to see the 5th star (component E) in Theta 1 Orionis (Trapezium in the Orion Nebula) by indirect vision despite the light polluted sky. Previously I had needed a 200 mm Newton for this with my 70 year old eyes. It is also remarkable that the 152 ED shows the colors of the stars beautifully despite its physically not perfect chromatic correction. For example, I could see the color of the red star near the center of M 103 very clearly.

Finally, it is remarkable how well the temperature compensating objective mount performs its function (the mount is equipped with a Zeiss-style thermal compensation ring). I moved the refractor from a well-heated room to the garden for observing today. Despite the temperature difference of more than 20° Celsius, there were no bright outbursts focally at all, and no dark indentations intra- or extrafocally, which are typical for a strained optic.

Result: The objective of the TS 152 mm f/5 ED refractor is spherically excellent and chromatically amazingly well corrected as well as equipped with a very good mount. I have great respect for the Japanese manufacturer who managed to produce a two-lens refractor lens of this quality despite the difficult combination of 6 inches of clear aperture and the extreme focal ratio of 1:5. And I am very happy to own this fine refractor!

Ulrich Steffen