Klasický CASSEGRAIN F/12 od TS

[sofram]

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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!

[MilAN]

Jako by autor čekal, že ten Cassegrain nebude tak dobrý jako menší refraktor. Ale to se nám tu snaží také někteří stále naznačovat, že není nad refraktor. Jenže ho nemají tak velký , jako všechny ty Newtony, MAKy a SCT. A tak nejlepší snímky jsou stále právě přes ta velká zrcadla

[Yarkho]

No neviem, keď niekto napíše, že videl farbu v rovníkovej zóne Jupiteru, a nič viac, tak mi ten ďalekohľad "nepredal".

A takú ε Lyr si dá i skromná C6 na raňajky.

[armichael]

No asi ano. Jenze jde o to ze ale z toho plyne ten zaklad. Ze je to dobry dalekohled a dobra koupe. Klidne sem dam ten clanek v anglictine. A najdi mi v cem je ten preklad zasadne lzivy. Ci neco prekrucuje.

Milane v pohode,
ja netvrdím, že preklad klame a prekrucuje. Mne sa skutočne páčila tá hra so slovami, kúzlo nechceného.
" just a beautifull first ring around Mizar at 140x." ---> "jen krásné první zazvonění kolem Mizara 140x."
Vieme o čo ide, človek by to takto nepreložil, kdežto stroj tomu nečakane dodal poetiku.

[sofram]

Jasne. Nechtelo se mi to prekladat. Tak jsem pouzil prekladac. Pro ty co nevladnou anglictinou. Ale mas pravdu. Nektere veci jsou usmevne. Souhlasim. Tak jsem dal i original.

[SIRIUS_758]

Myslím, že zrovna tato "recenze" si vůbec nezaslouží takovou pozornost...

A už jsem jednou připomenul, že náš kolega "MayJ" se ptal na úplně jiný dalekohled... Ale budiž, je to taky klasický Cassegrain.

[sofram]

S proc si nezadlouzi pozornost. Ja jich cetl vice. A vicemene se shoduji v tom v cem je sila tohoto kukru a v cem ma slabiny. Tato nijak nevybocuje. Ale mohu se mylit.

[Yarkho]

Myslím, že preto, že nehovorí nič podstatné, okrem toho, že kupujúci je s ďalekohľadom spokojný.

[Pidrman]

Mam prosbu.

https://www.dalekohledy-mikroskopy.cz/p ... 3-2436-ota

Tento dalekohled + powermate 2" 4 x a EQ-+6R, bude to fungovat ?

Chtěl bych si pořídit něco na pozorování i focení měsíce + planet. Ale nejsem si jistý s touto konfigurací.

Díky za rady.

Honza

[weszter]

No, já ho mám na svý iOptron CEM40, což je montáž s nižší nosností (18kg), mechanicky je asi slabší, a i bez barlow je to použitelné jen tak tak... Klepe se to jak drahej ratlík, i ostření jsem musel elektrifikovat, abych byl schopnej zaostřit...
Trochu bych se bál...

Budu to mít na MHV, jestli tam budeš, můžeme ozkoušet...

[Pidrman]

Jj budu tam. Tak když bude počasí, tak se moc rád mrknu díky Honza

[SIRIUS_758]

Montáž EQ-6R musí unést 20 cm Cassegrain bez problému...
Podívej se, kolik zdejších astrofotičů na ní vozí i 11"SCT a natahuje ohnisko na focení planet.

[Pidrman]

Vím že má velkou nosnost, ale přeci jen pomocí powermate 2" 4x to bude f48/9744 mm a to je masakr, aby místo obrazu nebyl sulc
Otázkou je co seeing, ten to bude asi dost shazovat a limitovat.

Možná bude powermate 4x za hranou a 2x bude stačit. Na detaily měsíce asi ano, ale na planety to bude asi málo. Je to jen 8" průměr, tak neočekávám zázraky jako má třeba Ari a jeho jupiter ( ten prostě nemá chybu ) tomu říkám zázrak !!!!!

Počkám na MHV, velká koncentrace lidí kteří fotí planety a mají velké zkušenosti ( nechám si poradit )

[astar]

Honzo, proč prodloužení 4x? Dostatečná světelnost je 6* velikost pixelu v mikronech. Ty máš 4.6 pixel(pokud nekoupíš s menšími) *6 je 1:27 to je při základu 1:12 cca 2x, tak stačí jen prodloužení 2x .
Při použití kamery i čipem IMX 678 kde jsou pixely 2 mikro, by si nepotřeboval žádné prodloužení .

[johny723]

Chcem sa spytat majitelov aky kufor alwbo tasku pouzivate na nosenie 8" modelu ? Diky