Cheap C6?

[Alfian]

Delving around in what equipment suppliers have to tempt us I came across this today.  I'm not really in the market for an SCT but thought this looked a good buy. Decent looking focuser and a 2" visual back. At £350 thats a big saving on a C6 or am I missing something?

https://www.astroshop.eu/telescopes/ts-optics-cassegrain-telescope-c-154-1848-ota/p,60781

[John]

It's a traditional cassegrain, not an SCT. Different optical design. No corrector at the front to figure and coat. Parabolic primary rather than the SCT's spherical one.

I'm not saying that it's better or worse than and SCT (I've never used a traditional cassegrain) but it's not the same as an SCT.

 

[newbie alert]

Astroshop eu are very professional ..they keep you well informed on shipping your goods..

Having never seen or used any other sct other than celestron or meade it's hard to make a comparison..it's at f12 rather than the normal f10

Good price id say

[Highburymark]

Slower than a C6 at F/12, and presumably diffraction spikes if you want to image. Good price though

[johninderby]

Quicker cool down than an SCT among other things but about 1kg heavier although part of that will be the focuser.

Link to Telescope Service. (TS)

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10748_TS-Optics-6--f-12-Cassegrain-telescope-154-1848-mm-OTA.html

[Alfian]

45 minutes ago, John said:

It's a traditional cassegrain, not an SCT. Different optical design. No corrector at the front to figure and coat. Parabolic primary rather than the SCT's spherical one.

I'm not saying that it's better or worse than and SCT (I've never used a traditional cassegrain) but it's not the same as an SCT.

 

Thanks John, when I said "am I missing something?" - clearly I was and welcome being put right.

[michael.h.f.wilkinson]

On axis, a well figured Cassegrain can be sharper than a Schmidt Cassegrain, but off-axis I would expect more coma. I do believe the Cassegrain design is very sensitive to collimation errors, and you need to collimate both the primary and secondary, as opposed to only the secondary in an SCT. My C8 hold collimation exceptionally well, I must add.  The weight of this OTA is just shy of that of a C8 (5.7 kg for the C8, 5.4 for this one) so for travel it doesn't have much of an advantage. I am not sure the baffle tube of the Cassegrain is wide enough to illuminate the full field of a 2" EP. A C8 OTA is more expensive, of course.

 

[Cosmic Geoff]

Interesting. There is also an 8" version which for some reason is far more expensive - more than twice the price. In fact Telescope Express offer an orange C8 OTA for less than the price of the 8" Cassegrain.  Note that TE prices exclude VAT.

One has not seen these Cassegrains before and one wonders if modern manufacturing technology has made them cheaper and easier to manufacture. Will prices fall? A tube, spider, focuser  and parabolic mirror should not cost a lot to make - the much cheaper Newtonian design has these.   The secondary - presumably aspheric or hyperbolic - is the only obviously exotic part.

Somebody might be tempted to take a punt on the 6" Cassegrain at that low price.

[dweller25]

I would really like a 6” Classical Cassegrain but the focal ratio offered by Telescope service is only F/12 and I’m not sure how much the largish central obstruction plus the secondary support vanes are going to affect planetary contrast. 

I doubt it will be any better than my excellent C6 but hopefully someone will post a review......

[Cosmic Geoff]

There is a 27 page thread on these Cassegrains on Cloudynights.  Mostly speculation and comment, but on page 26 or 27 somebody reports a side by side comparison of a Cassegrain and a SCT.  Seems that the performance is very similar.  So the competition is going to be on price.

The 8" GSO Cassegrain (=TS, etc) is already available in USA and Australia, it seems, but not Europe.  Australians complain of overpriced SCTs in Australia, where the Cassegrains are notably cheaper than SCTs.

[wimvb]

On 23/03/2019 at 09:18, Cosmic Geoff said:

Interesting. There is also an 8" version which for some reason is far more expensive

On the same site, an (almost) identical cassegrain from Omegon is offered. Same specs and same price. The larger 8" Omegon has a quartz primary mirror, whereas the 6" has a BK7 glass mirror. This, and the larger size, can be the reason for the price difference. Both scopes (TS and Omegon) are probably rebranded Chinese or Taiwanese products.

[Alfian]

I've recently been in touch with Astroshop.eu  enquiring about an Omegon product which is their home brand. Without saying it was definitely the same as a GSO item it seemed clear that it was from the same source but with Omegon's cosmetic changes and one or two accessory differences. Astroshop also made the point of saying that Omegon had their own quality control checks.