TS-Optics GSO 8" f/12 Cassegrain telescope 203/2436 mm OTA

TS-Optics GSO 8" f/12 Hyperbolic Cassegrain Telescope

Cassegrain telescopes combine the benefits of a Newtonian telescope being a pure reflective system with a short-built design. In terms of optical quality Cassegrain telescopes are superior to customary Schmidt-Cassegrain systems. Cassegrain telescopes are mainly used for photography of the moon and the planets and for observation of astronomical objects. Thanks to the highly sensitive sensors built into modern astro cameras, even deep-sky photography of nebulae, star clusters and galaxies is possible.

The advantages of the TS-Optics Cassegrain telescopes in summary:

Well corrected field due to parabolic primary and hyperbolic secondary mirror with less field curvature than with SC telescopes.

Pure reflection system without Schmidt plate, as a result even Infrared photography becomes possible at full sharpness.

Significantly quicker temperature adaption than a SC, due to open design.

Brighter image due to 99% dielectric coating on primary and secondary mirror.

No shifting, because the primary mirror is fixed

High-quality 2" Crayford focuser with micro-gear reduction and compression rings for 2" and 1.25" accessories

33% obstruction caused by secondary mirror, comparable to SC telescopes.

Better sharpness on the optical axis due to precise mirror surfaces and the lack of a Schmidt plate

Less problems from dew: with Schmidt-Cassegrains you get condensation on the front plate, not with a Cassegrain

Interior baffles for even higher contrast

Generous backfocus allowing the use of 2" accessories.

Compact tube with only 580 mm length - can be operated with smaller mounts

Primary and secondary mirror are adjustable

The TS-Optics Cassegrain is a versatile telescope

Mobile travel scope: Take the compact and light telescope with you to your traveling location. It only takes a few seconds to unscrew the focuser, making the Cassegrain even more compact.

Telescope for observation of astronomical objects Due to the bright and contrasty image and also because of the large corrected and illuminated image field, the Cassegrain is optimal for observation of astronomical objects. 2" and 1.25" accessories are not a problem. The obstruction by the secondary mirror is only 33%. This is comparable to Schmidt-Cassegrain telescopes. As a result of the 99% reflection of primary and secondary mirror the image is significantly brighter. Even the field sharpness is better, because the image field is basically flat.

Telescope for astrophotography: The Cassegrain is very well suited for photography of the moon and the planets. The contrast of the image is very high. Due to interior baffles stray light is effectively suppressed. Planets and tiny moon craters can be seen without the slightest chromatic aberration.

Astrophotographic results obtained with this telescope on Astrobin

Here you can find some astrophotographs made with this telescope model: Link to Astrobin

Astrophotographic results obtained with this telescope on Astrobin

Here you can find some astrophotographs made with this telescope model: Link to Astrobin

This is an image from our customer Dodi Dierick, B

Object: Moon with craters Theophilus, Cyrillus, Catharina
Photographer: Dodi Dierck, Ghent, Belgium
Date taken: 2021-07-29
Imaging conditions: moderate seeing
Telescope: 8" Cassegrain TSCas8M
Camera: ZWO ASI290MM
Method: Mosaic of 6 images
Processing: stacked with Autostakkert, final processing using Adobe PS, with 10% magnification

Congratulations for this very good result!

This is another image from our customer Dodi Dierick, B

Object: Jupiter (only 19° height
Photographer: Dodi Dierck, Ghent, Belgium
Date taken: 2021-09-16
Imaging conditions: moderate seeing, bad transparency
Telescope: 8" Cassegrain TSCas8M
Focal extender: TMB Barlow lens 1.8x
Camera: ZWO ASI290MM
Additional information: First Jupiter image with this telescope

Congratulations for this result,too!

Just tested Classic Cassegrain 8" from TS

I have to say, I am VERY happy with its optical performance!
Mechanically its excellently made!

Its much better mechanically than Celestron C8 I had, and I have to say I like it better optically, and as well because no image shift, and flat image.

Focusser strong and smooth working, nice, def no need any upgrade even for most demanding observers like me!

One more important thing I notice: no annoying dew/moisture/water drops like on all SCT and all Maksutov telescopes with corrector plates-very important feature!

With small Baader T2 prism, I am able to reach focus with my Carl Zeiss binoviewers without need of using any GPC, barlow etc-great feature for all binoviewer users!

Overall, high quality telescope both optically and mechanically, suitable for any application, for very affordable price!

Thanxs for that great scope!
CS
Denis, binoviewers expert

Here a test report from our customer Guus Gilein, NL

Until a few years ago I owned a TS 127 mm f/7.5 triplet refractor which I used mainly for making brightness estimates of variable stars. Sometimes I wished I could see just a little bit deeper than this refractor was able to show. For that reason I bought a 180 mm f/15 Skywatcher Maksutov and the telescopes where complement to each other. With the Maksutov I could see about 0.5 magnitude fainter stars, the refractor gave wide fields at low magnification. Both delivered views rich in contrast and sharp stars till almost the edge of the field of view. Something that helps enormously with observing variable stars. The comparison stars didn?t need to be near the centre of the field.

At the end of 2016 I was able to buy a 152 mm f/8 ED Lunt/APM doublet refractor at the HATT in Hattingen for a very interesting price. Lunt was selling out its APM stock, so slightly heavier loaded than on the way to Hattingen did my astrofriend Nico and I return home.
Such a 15 cm (semi) apo refractor was a dream of me for years, and it performs as expected. In fact it performs so good that it almost bridged the difference between the old 127 mm refractor and the 18 cm Maksotuv. So this last one had actually become superfluous.

But I did miss the old situation, now and then I wished I could see just a little bit deeper than the new 15 cm refractor was able to show. Nothing human is alien to me!
But what should I do? If I wanted to go to the old situation (and I wanted that for certain!) than I needed a telescope that would again show stars some 0,5 magnitude fainter than with the 15 cm refractor. With some calculations it was clear it should be a 21 cm telescope. But which one?

A Newtonian dropped out for a variety of reasons. A 20 cm Maksutov is only available as a second-hand Intes and due to the increasingly thicker meniscus lens getting heavier and heavier.
No Schmidt-Cassegrain has ever been able to charm me, I don?t like their star images, and in contrast to a Maksutov their corrector plate fogs much faster.
My friend Nico?s 210 mm Takahashi Mewlon seems to be the perfect candidate: not so heavy, a perfect and contrasty image. But: second-hand almost none-existent and new just a little bit too expensive to my taste, I didn?t want to spend that much.

Enters the summer of 2018: Teleskop-Express announces the arrival of a new telescope type in their program: a 6? and 8? Classical Cassegrain with a parabolic main mirror and a hyperbolic secondary. No meniscus or lens that could fog, only two reflections of each 99%. The weight is even less than my 15 cm refractor and my old Maksutov: just 7.5 kg. The price is right too: a Mewlon sales for 3.5 times as much!
It comes with a Vixen style as well as a Losmandy style dovetail: very handy for me. With the first I can put it on my Skytee mount, with the other on my Celestron CGEM mount.

Delivery would be the beginning of september 2018. I informed TS about my interest in this new toy and put my trusty Maksutov on the market. That one was sold within days, the replacement took a little longer: it took until mid-June 2019 before it fell on the doormat.

I also had ordered TSRCkolli, a 2? collimation tool, but that one was not available at that moment. The secondary of the Cassegrain has a small central circle, perfect for aligning. I used a Cheshire eyepiece instead and suspected a small mis-alignment, perhaps due to some rough handling of the transport company as TS inspects the Cassegrains before shipment.
For the moment I let it for what it was.
The 1:10 focussing knob made a rattling noise when turning, but that was easily resolved with a Allen wrench. I just had to put the knob a fraction of a millimeter more outside.

To my surprise it was clear for an hour or so and first light could be carry out on the day of arrival. Just after sunset the small crescent Moon was just visible next to our neighbours house and I could align the finder. I could also check if my eyepieces came into focus.
Well, they did not with my 2? and 1.25? Baader Amici astroprisms, the focal point was more outside than the 5 cm travel of the focusser could handle. But no problem, there are three M90 rings included with the Cassegrain. Just unscrew the focusser with a big ring (also very handy to rotate the focusser in any desired position), attach one or more rings and screw the focusser on the ring. Apart from one eyepiece (my 16.7 mm Zeiss Diaskope) I was able to reach focus with all the others.

Although in bright twilight (I live 52 degrees north) at half past eleven in the afternoon I could compare my first views with the Cassegrain with that through my 15 cm ED refractor. And they were not bad at all. M57, the Ring Nebula, was noticeably brighter and showed more details through the Cassegrain than through the refractor. The Double Double was easily split.
Even in 2? eyepieces I could notice no vignetting: stars in the centre on the edge of visibility were still on the edge of visibility near the edge of the field of view.

With the 15 cm refractor and a 7 mm Vixen SSW (171x) I couldn?t observe the magnitude 13,1 comparison star near Z Cam, and the magnitude 12,5 star was just peripherally visible, just 20% of the time.
With the Cassegrain and a 17.3 mm Delos (140x) both stars were directly visible and I noticed some even fainter. That was better than expected! Does the 99% reflectivity really helps? Both telescopes had the same 1.25? Baader Amici.

With a 10 mm SSW (243x) on the Cassegrain the image quality was still good, there was no deterioration to be found. Stars were still sharp with sometimes a small first ring was seen (depending on the seeing) Then came the clouds to remind me that you can?t expect anything the first week you have new astrotoys ...

After three days it cleared again and I was able to perform some more tests. One difference with a Maksutov was immediately clear: spikes! I had Arctures centered and it showed four bright spikes with two more from the Amici. Fast forward to Alco and Mizar and to my relief there were no spikes visible anymore: just a beautifull first ring around Mizar at 140x.

The telescope is very easy to handle, I?m able to observe within a few minutes. Just putting it on my Skytee mount, aligning the finder (see picture) and you can start. The telescope is stored in an unheated shed so there is not so much difference in temperature, and although on unfocussed stars you can see it?s cooling down, the image quality is still good from the beginning: even with a 13 mm Ethos (187x) stars are sharp.

Jupiter was visible just next tot he Moon just above the house of some neighbours, and although the close proximity of the Moon I could see no reflections. The background was bright but a) it was twilight, b) there was some fog and c) Moon nearby.
Jupiter was only 14 degrees above the horizon so atmospheric refraction did hinder, but when seeing calmed down I could see more details than I could have painted. The yellow to yellow-brown color of the equatorial zone also came through clearly in those moments. I can´t remember ever seeing Jupiter like that. That was one of the better Jupiter observations in my more than 45 years of observing.

Then to the Moon and Plato viewed with my 12.7 mm Zeiss Diaskope (192x). As the Moon was near full, the small craterlets could no longer be seen as black indentations, but as light spots. I counted at least five at times when the atmosphere came to rest.

Since then the TSRCkolli had arrived and there was indeed a very small misalignment of the secondary. Just a small turn with a Allen wrench did the job. Very easy at daylight!

I also observed some more with the Cassegrain and every time I?m amazed how much deeper I see compared to the 15 cm refractor. And that one showed the same amount of stars as the 18 cm Maksutov. I have to measure it precisely yet, but I think it?s almost a full magnitude compared to the 15 cm. The view around SS Cyg was filled with much more stars than I have ever seen with the 15 cm.

Deepsky is very nice too, M13 is beautifully resolved.

Now I have to wait till August/September when there is astronomical darkness again to see its full potential. Nico and I are planning a comparative test between his Mewlon and my TS Cassegrain. The focal lengths are almost identical, very easy to compare with the same eyepieces.
Nico?s observing side is outside the city (I almost always observe within) next to the dunes so the local seeing will be better and we can push the telescopes to their limit. I will make another report on that comparison, as well on its behaviour on small faint deepsky objects.

Till now the Cassegrain does everything I hoped it would do, and even better!


The 20 cm f/12 Cassegrain on the Skytee mount and a Berlebach tripod. The finder on the left is a 6 cm Baader Vario finder, so I need only a RDF for first alignment on a bright star.




Notice the optional 3? Baader handle: very handy for putting it on and off a mount!




Baffles, baffles and even more baffles!




The Cassegrain on a Celestron CGEM. Now a 6 cm finder is attached on the Vixen dovetail.

Question:
How do I get the Cassegrain onto a mount with EQ5/Vixen level quick connection?

Answer from Teleskop-Service:
You can swap the rails on the Cassegrain or remove one of the rails completely. Simply unscrew the lower Losmandy level rail and the upper Vixen rail with the bearing blocks and screw the Vixen rail to the underside. The threads fit. You do not need to screw the Losmandy rail to the top. The telescope remains stable even without the rail.