10" GSO RC ** Tube or Truss

RobC (Rob) · #1 16-07-2015, 05:27 PM

I am considering purchasing a 10" GSO RC and I am not sure whether to purchase a tube or truss one. I am tending to favour the tube model over the truss model to minimise dew problems. I would be interested to hear how dewing problems can be overcome with either model.

Thanks

Rob

multiweb (Marc) · #2 16-07-2015, 06:51 PM

10" is still light enough to get a full tube. If you're worried about dew with a truss a shroud can always sort it out.

Flugel88 (Michael) · #3 16-07-2015, 10:14 PM

Rob if you get dew problems you could try one this from Bintel for the Secondary mirror
http://www.bintel.com.au/Accessories...oductview.aspx

RobC (Rob) · #4 17-07-2015, 10:31 AM

Thanks Chaps.

Are there any technical reasons for choosing one over the other.

Cheers

Rob

rustigsmed (Russell) · #5 17-07-2015, 10:37 AM

are you talking about the Carbon Fibre tube or the steel tube?

Russ

RobC (Rob) · #6 17-07-2015, 12:15 PM

Russ,

I am talking about the steel tube version. It will either be the steel tube or truss. The steel tube version is appealing because it is roughly $1500 dollars cheaper. However I have heard that the truss version is a new design with better specs than the steel tube version.

Rob

glend (Glen) · #7 17-07-2015, 01:28 PM

Rob what did you decide? The sale ends in a few hours you know? I just bought an RC-8 steel tube to add to my collection and to get some RC experience. Figured carbon fibre wasn't that big a deal in that size for the price premium. Re the truss, my 10" truss imaging newt is light for its size but absolutely requires a shroud at all times. So is there a weight saving you chasing or you just want to get on the truss team - what are the real advantages that justify the price difference, same mirrors in both, same optical design, etc.

multiweb (Marc) · #8 17-07-2015, 01:31 PM

Quote:

Originally Posted by RobC

Russ,

I am talking about the steel tube version. It will either be the steel tube or truss. The steel tube version is appealing because it is roughly $1500 dollars cheaper. However I have heard that the truss version is a new design with better specs than the steel tube version.

Rob

It's still a significant saving. What are the better specs exactly? Primary mounting?

rustigsmed (Russell) · #9 17-07-2015, 02:07 PM

Quote:

Originally Posted by RobC

Russ,

I am talking about the steel tube version. It will either be the steel tube or truss. The steel tube version is appealing because it is roughly $1500 dollars cheaper. However I have heard that the truss version is a new design with better specs than the steel tube version.

Rob

if its the GSO, I believe you can upgrade to truss later down the track if you feel the need? but yeah $1500 is a lot of camera you could spend on. I have the gso 12" newt which is steel, needs a few upgrades but I don't have any issues per se with the steel itself. my mount can easily handle the weight. that's probably your main consideration 2m FL and the weight.

all the best

Russ

RobC (Rob) · #10 17-07-2015, 02:18 PM

Marc/Glen,

Thanks for you response. I heard that the truss primary mirrors were better mounted which tended to minimize collimation problems. I have no idea , whether this relates to previous truss versions , steel tube versions or is just a lot of hot air.

This scope will be my first foray into RC's and I want it to be portable as I will be taking it to dark sky sites. I am tending towards the steel tube version because of the dew , dust and stray light problems I am anticipating with the truss version. Basically I was looking for confirmation of my anticipated concerns from IIS members.

I did a bit of horse trading and have until Monday to make up my mind.

Thanks for the responses.

Rob

RobC (Rob) · #11 17-07-2015, 02:30 PM

Quote:

Originally Posted by rustigsmed

if its the GSO, I believe you can upgrade to truss later down the track if you feel the need? but yeah $1500 is a lot of camera you could spend on. I have the gso 12" newt which is steel, needs a few upgrades but I don't have any issues per se with the steel itself. my mount can easily handle the weight. that's probably your main consideration 2m FL and the weight.

all the best

Russ

Russ,

Thanks, my sentiments exactly . The $1500 will most likely go on a new Central DS modded and cooled Canon . An astro mate of mine purchased the 12' inch RC steel tube about two weeks ago and he is getting some pearler images.

Thanks

Rob

glend (Glen) · #12 17-07-2015, 04:17 PM

Rob, its pretty clear from the photos of the RC-10 scope models that the RC-10 tube models are internally baffled, where as the truss is not. I don't know if you consider that an issue.

RobC (Rob) · #13 17-07-2015, 06:52 PM

Quote:

Originally Posted by glend

Rob, its pretty clear from the photos of the RC-10 scope models that the RC-10 tube models are internally baffled, where as the truss is not. I don't know if you consider that an issue.

Glen,

How do I interpret that . Is that a plus for the tube or a plus for the truss.

Thanks

glend (Glen) · #14 17-07-2015, 07:31 PM

It minimises the effects of stray light and thus can improve contrast and provide a darker background - according to my internet search on the subject. My MN190 is heavily baffled and seems to exhibit those benefits. I would suggest that is a plus for the tube but i don't know how that is duplicated in the truss models.
PS, one thing I have discovered about shrouds is that they can allow light through if it hits it at the right angle. I was getting red casts to images taken on my truss newt at certain attitudes at the dark site - tuned out to be people walking by with red led headlights on. Tubes don't allow light through obviously. The quality of the shroud, material used, etc could negate any difference I suppose. I'll defer to the shroud experts, but my theory is that the stretch shrouds open up the weave of the lycra like material creating pores for light to enter at 90 degrees to the fabric.

gregbradley · #15 17-07-2015, 07:43 PM

Carbon truss would be better. How much better? I don't know but possibly significantly.

All the top RC, CDK etc are carbon truss. Why? Firstly lighter weight. Secondly they have less tube currents from temperature differentials between the tube and the mirror and thirdly for stability of focus.

Carbon truss type or carbon tube type scopes do not shift focus much at all with temperature shifts.

Aluminium tubes match refractors quite well as the shrinkage of the tube when it gets colder is not too different to the shift in focal length of the objective - FSQ excepted.

But steel, probably not a good match. Perhaps others who own one of these steel tubed scopes can comment. Does it need to be refocused when temperature drops and is very sensitive to temperature drops. Some scopes are.

A heavier tube will affect your mount and ability to get round stars. How much weight can your mount take easily?

If the above is not a concern dew is no different for a steel tube versus a carbon truss as the carbon truss should take a material shroud that covers it. That also blocks stray light.

You could though wrap a steel tube with a thermal blanket to reduce the onset of dew more easily than a truss bit I suppose you could do the same on the truss.

Dew is handled in a few ways.

1. Dew heaters
2. Dew shield
3. Thermal blankets to delay the cooling of the tube to dew point and keep it a few degrees warmer when temps drop.
4. Fans

I would think the big factors would be weight and the affect that may have on your mounts tracking, the focus shift with temperature drops and the thermal currents inside the tube affecting image quality.

Greg.

RobC (Rob) · #16 17-07-2015, 08:17 PM

Glen and Greg,

Thanks . You have certainly hit all the salient points.

Greg - I am light years behind you, in your professionalism and astro gear. I appreciate your comments and directions. I am thinking about jumping onto a CDK and good mount in a year or two after I have developed the necessary skill sets.

Glenn - Good point about the shroud. This was the type of info I was looking for.

Cheers

Rob

Paul Haese · #17 17-07-2015, 09:59 PM

Go with the carbon truss. I had the 12" steel tube before I bought a truss. The tubed version of these optics moved focus throughout subs. It was a pain.

glend (Glen) · #18 17-07-2015, 10:30 PM

Quote:

Originally Posted by Paul Haese

Go with the carbon truss. I had the 12" steel tube before I bought a truss. The tubed version of these optics moved focus throughout subs. It was a pain.

Paul, seeing as how I just ordered a steel tube RC08 can you give me abit more info about how long these subs of yours were and whether this was happening on a temperature equalised scope? I acknowledge that I am a rank amateur compared to what your doing. I did some reading on thermal stability before I ordered the RC08.
I shoot through a steel tubed Mak-Newt now and have no problems, that I am aware of, with optics moving during my subs. Admittedly my subs might be considered short by many at under 5 minutes always. Also I shoot OSC with a cooled full spectrum DSLR and don't need to switch filters or contend with refocus issues. I tend to set up the camera focus at the beginning of a session and don't touch it again for hours. I also don't use any focus software, just a Bathinkov mask, so I probably would not know anyway, but my subs stars look ok in processing most of the time. I should add that scope will sit on my pier in the observatory and always be at ambient when setup for use; my imaging runs are almost always between 11pm and 4am a time which is fairly temperature stable - especially at this time of year. What I am asking: is the potential for optics movement from using a steel tube likely to frustrate someone at my level. Thanks

RobC (Rob) · #19 18-07-2015, 11:01 AM

Quote:

Originally Posted by Paul Haese

Go with the carbon truss. I had the 12" steel tube before I bought a truss. The tubed version of these optics moved focus throughout subs. It was a pain.

Thanks Paul.

Good to hear you are using one of these scopes. Gives me a lot more confidence in purchasing one. I may wait now and not make a decision till after the Qld Astrofest where hopefully I will see some in action.

Cheers

Rob