Review - GSO RC12 Truss Ritchey Chretien Astrograph

Guan Sheng Optical (GSO) is telescope manufacturing company. They are based in Taiwan. They make affording telescopes for the consumer market and also mirror sets for some of the other more expensive Ritchie Chretien (RC) manufacturers.

All their mirrors are CNC manufactured and of a very high quality. Mirrors test well with good Stehl ratios and infragrams. Though none of this information is freely available or included in purchase, you can request the information.

I first bought a GSO RC when they were introduced to Australia in 2008/09. The optical surfaces were very good as was the optical tube which was carbon fibre. I used that telescope to image quite a few objects in the night sky after I made a few modifications to the primary baffle tube and the purchase of a quality focuser.

In early 2011 I decided to upgrade to the GSO RC12. At the time it had a steel tube (still available I believe) with tube rings and dove tails top and bottom. It also came with a large focusor made by GSO. After some early trialling I found that the steel tube would not hold focus long enough in the early part of the evening to do any useful imaging.

Nor was the focusor any good despite its size. It had a fair bit of flop in it and this affected the collimation of the telescope. I was disappointed by these faults but I did know the optics were going to be useful in the long term. I had several conversations with Jim Sheng about the issues and he had indicated that a carbon truss was under development. It took several years for this truss system to be realised and available to the market. When it became available I ordered just the truss from GSO and installed the mirror set into the OTA.

Upon testing I found that the carbon system was very stable. It would hold focus for many hours before focusing would need to be conducted again. However some other problems arose. The first was that the secondary would dew up badly. To solve this issue I installed a Kendrick dew heater into the secondary assembly. This involved drilling a hole into the rear plate of the secondary and then taping the cables of the heater along one of the spider veins. It worked perfectly and dewing of the secondary has not been a problem since. It is also on my nag list to Jim Sheng for future development and incorporation of his scopes. It would be good if GSO installed secondary dew heaters in manufacture.

The next problem was that of imaging payload was being supported by the mirror assembly. Whilst, smaller payloads would not cause a problem, I found that putting about 12kgs of imaging equipment on to the OTA would cause distortions to star shapes and collimation would be affected by elevation. Gravity was working against the design. Working closely with GSO and Bintel, we came up with a design which would support heavy imaging trains and not affect collimation. The imaging assembly is now supported by a camera adjusting ring/imaging train support ring, which is supported by the rear OTA plate. The primary is unaffected by the imaging assembly as a result. Since installation of the new mirror assembly and rear plate I have had not issues with star shapes or collimation at all.

Future developments are likely to incorporate a flattener/corrector for these scopes. Currently, there is not a corrector available from GSO. This can mean for larger sensors you need to either purchase a dedicated flattener from other RC manufacturers (which are very expensive) or you simply have to crop. I have tried a couple of cheaper flatteners and they do not work, so I have opted to wait out a dedicated flattener from GSO. There is one in development and have seen the prototype. At this stage it is only 2”, but a 3” version is in planning.

What I like most about these scopes is that bang for buck they can and do compete well with the more expensive RC’s.

The OTA’s are developed enough now that great results can be obtained with them. My images would seem to attest to that. Instead of paying twenty to thirty thousand dollars you can get a scope for under ten thousand dollars which has great optics, can hold collimation well and holds focus for long periods of time.

You will need still need to do some tinkering to get the scope working at peak performance but not nearly as much tinkering that I have had to do in the past. A new focusor is a must and a dew heater for the secondary if you have lots of dew in your imaging site. You will need to learn about collimation of an RC too. Collimation of these scopes is demanding and requires careful adjustments to get things near perfect. Having the right tools for collimation will help to obtain perfect collimation.

Overall these are very good telescopes now and I will be buying a bigger one in the near future.