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Difference between Real RCOS and Chinese

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#1 Michaeljhogan

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Posted 22 February 2020 - 05:56 AM

Hello I know the Chinese RC are very good but the European RC like Planewave RC or ASA RC or Alluna Optics etc are great but would the price really make a difference and then going from the western RC to the RCOS which are even more expensive but would the mirror be that much better that is the question.

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Edited by Michaeljhogan, 22 February 2020 - 06:04 AM.

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#2 carolinaskies

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Posted 22 February 2020 - 06:22 AM

I believe the main difference is the final figure of the optics and perhaps glass choice for the mirrors themselves.

I would equate the difference to lets say top speep or 0-60 times of a car.  The average car is built to a general spec, reliable, gets you where you want to go for lets say $25,000.  But the difference you feel when you drive a Hyundai Sonata and a 600hp Labroghini is signficant.  It's more than cubic inches of the engine, but how the engine is tuned and built to eek out the last bit of performance. 

The same is true when you step from a consumer grade telescope to a true scientific research grade optic.  The last attention to detail when figuring the curve of the primary and secondary before the coatings are applied make a difference in output when you are matching all the pieces together.  The typical RCOS buyer isn't putting a $500, $1000 DSLR or Dedicated camera up to their scope, they are spending $2500-$5000 and more for a camera and other accessories as well to get all the performace possible. 

I have 8" & 10" SCTs, then I have my 16" LX200 SCT.  The 16" is considered an entry level research grade instrument by most institutions.  While some might argue the point, it is a flagship piece which to take the next step above would cost 3x-5x as much to eek out an extra bit of performance.  Would I trade my 16 away for one?  No, because it really isn't necessary becasue I'm not using my 16" for detailed research.  

For most amateurs the RCs from GSO are within reach without breaking the bank for performance they will never need.   

If you want to understand more you can look up wavefront error, etc.  

Finally I'll also say this, if you don't have a prime location to take advantage of that performance, it's like buying a lambroghini and driving it only in a parking lot or on a 20mph street.  It may look flashy, but the performance doesn't matter if you can't take advantage of it.  


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#3 Jon Isaacs

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Posted 22 February 2020 - 07:19 AM

My take:

 

Telescope optics  are rated in how close to perfect they are, cars are not, even the best cars are far from perfect

 

A 12 inch RC made by GSO is probably 90% or more perfect optically and when all is right will take images similar to a premium RC. The premium RC is mechanically more robust, optically more perfect and performs it best at all times.  The GSO, tinkering is required. RCs are very senstive to collimation.

 

Jon


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#4 skyward_eyes

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Posted 22 February 2020 - 07:55 AM

The cheaper RC telescopes on the market today offer an affordable, larger aperture option for imaging. While they do the job there are quite a few differences between them and the higher end versions.

RCOS really specialized in 10” and larger models. These were usually designed for research level work. They focused by moving the secondary mirror with a very precise motor assembly. They also feature a control box which allowed the owner to control the focuser, rotator and cooling throughout the scope. Another big difference is RCOS used high precision figuring and Ion milling to figure their optics. The tubes used carbon and other materials for improved rigidity. They also feature large field flatteners to handle large imaging sensors.

Much of this is the same for the current companies as well on the higher end market. They offer a lot of additional supporting products that would be in demand by higher end clients. High payload focuser, rotators, large format flatteners and reducers as well as low expansion glass options for their optics.

The cheaper RCs are really bare bone system in which you need to address these issues yourself. They offer a good platform but do not offer everything the higher end market does (but you do pay for it).

Edited by skyward_eyes, 22 February 2020 - 07:57 AM.

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#5 George N

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Posted 22 February 2020 - 10:20 AM

The main difference between RCOS (also OGS https://opticalguidancesystems.com/ still in business, and mostly making 20+ inch pro scopes and mounts, so they don't do adds in amateur publications anymore) versus the 'less expensive' Chinese RCs are the mechanical parts, including the tube.

 

I was told (by each party separately) that OGS and Explore Scientific were considering a joint venture, with ES providing the Chinese optics and OGS the tube assembly - the end product sold by both. In the end it never happened - but both told me that the Chinese RC optics are very good.

 

OGS no longer states the source of their optics -- probably because they come from their competitors. However, they do state on their website "Each system is diffraction limited, having a final wave error of 1/4 PV and 1/30 RMS. A Zygo interferogram with fringe analysis is provided to certify the optical quality of your telescope."

 

Also, while OGS recommends the RC, and advertises Classical Cassegrains too, they state "Recognizing that no single optical design is best for all applications, OGS can supply Newtonian, Classical Cassegrain, Wright-Schmidt, Maksutov or Ritchey-Chretien systems configured to specifically meet your needs."

 

The big cost elements in OGS (and RCOS) is the mechanical structure - made in the finest USA machine shops on the best equipment available - and are very strong to eliminate shifting as the scope moves (or is transported). The machining is aerospace industry precise, and the tubes don't bend. ?The OGS tube is a combination of Al, Mg, and carbon fiber designed to be compatible with their pro customer's IR concerns.

 

Read the stuff about collimation on this page: https://opticalguida...ystems.com/faq/

 

The owner of OGS is well-liked in his local astronomy club because he takes fellow members' SCTs into his shop and collimates them on his double-pass rig. "I can often improve their performance by offsetting the secondary a tiny bit to compensate for the mis-collimation of the primary."

 

One final note about price -- OGS (and I think RCOS) prices for telescopes 16-inch and larger includes on-site installation, with a guarantee that the scope will work before they leave. They will show you how to run everything -- and if there's time, they do a T-point run (OGS mounts use the same electronics and motors as Bisque).

 

To me - it all comes down to money. For most amateur astronomers the Chinese RCs will work just fine, but may need some "fiddling" to get full performance. For 'high healed" am's, and institutions with limited funds - there's Plane Wave -- and for those with "unlimited resources" there's OGS, Deep Sky Instruments, etc.

 

I should mention -- the owner of OGS's personal telescope is a Tak APO refractor on a modified Tak mount. wink.gif   --but I've seen him at Stellafane with an OGS 12.5" RC - used just before shipping to a customer (with permission of course).


Edited by George N, 22 February 2020 - 10:25 AM.

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#6 WadeH237

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Posted 22 February 2020 - 12:06 PM

The big cost elements in OGS (and RCOS) is the mechanical structure - made in the finest USA machine shops on the best equipment available - and are very strong to eliminate shifting as the scope moves (or is transported). The machining is aerospace industry precise, and the tubes don't bend. ?The OGS tube is a combination of Al, Mg, and carbon fiber designed to be compatible with their pro customer's IR concerns.

I think that the optics in the GSO scopes are pretty good, but I would expect an RCOS or AGO to consistently better.

 

But I think that the above point is a bigger deal.  I was at a presentation at AIC, where the owner of (I think) and RCOS scope was talking about collimation and showed us the results of a test.  He used CCDInspector on an image that showed zero collimation error.  He turned one of the collimation screws a fraction and CCDI then showed a collimation error.  Finally, he turned the collimation screw back to its original position and CCDI showed zero error again.

 

I doubt that you would ever see this consistency or repeatability with a GSO scope.

 

For what it's worth, I have a GSO 6" RC, and based on it, there is no way that I would buy another GSO RC.  The optics are decent, but the mechanical quality really lets it down.  I would assume that the newer and larger truss versions would be better.  But I'd rather not gamble on it.  Buying a 6" to play with is one thing, but I don't want to drop $3k or more on a scope that may or may not meet my expectations.  I would rather spend the extra money (even though it's a lot of extra money) and get something that will be a pleasure to use.


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