Are GSO Truss RCs OK now?

[gregbradley]

I see a number of members have one but only Paul who has posted an image using one.

If you have a GSO truss RC - how are you finding?

Are the issues resolved now or would it be buying a project to get it operational?

Greg.

[baileys2611]

I'm about to put a deposit on one but before I do that I'd be interested in this also. I see there's a plethora of forums on this and some people have had problems with the mirrors flopping.

...but, is there a better alternative for about $4k for DSO photography? I like taking shots of DSO and nebula, generally using a QHY8.

[baileys2611]

Actually there's a few discussions on this already. Horses for courses, summary from what I've read so far: It's a long life, get in and experience them all if you can. :thumbsup:

[Logieberra]

Does this count?
http://www.iceinspace.com.au/forum/showthread.php?t=132933
12 x 5min and 10 x 5min exposures for these, respectively.

[baileys2611]

Yeah, I saws those earlier today Logan. Damn fine images, I know that the Sombrero holds a special place for you and is an excellent shot but the other picture is fantastic!

[Logieberra]

Greg. I really love mine. Wonderful scopes for the price. Mirror coating was pristine out of factory, as it should be. The CF trusses are a beautiful thing. Mirror is as good as fixed. They use some kind of black compound to retain the primary. Secondary housing and bolts are solid as. Holds colimation beautifully. All joints, connections and bolts etc - very rigid. GSO got it right, for the price.

[Paul Haese]

Yes the scopes have reached a level of maturity now. The 12-16" models should have the new back plate which has the collimation ring incorporated. If it does not ask for one that does. The new back plate is designed to remove loads placed on the mirror cell.

Some things you will need to do though.



The focusor is garbage and no good for lifting heavy loads. A good focusor is a must. The FLI Atlas is perfect as a suggestion.
The secondary can be prone to dewing up in areas with heavy dew. I have installed a dew heater into the secondary and that has removed that problem. If you like I can dig up some photos of how I did the install.


Other than these minor issues these scopes are good.

Careful collimation is a must though. You cannot do a good job without a Takahashi collimation scope. I cannot stress this enough. It is next to impossible to get the primary aligned without one. The primary will move during transport and will need adjusting. A laser will not work properly. The Glatter one is not going to work for you at all and gives inconclusive results. Anyone considering buying one of these scopes needs to take my advice on this.

[niharika]

What flattener options are available for medium to large format CCDs?

[baileys2611]

Fair enough on the colimation & focuser. I've got a moonlite I was going to use and will obviously need to invest in a colimator and shroud, but I use a QHY8 which is large format so will also need to look at a flattener I think.

[Paul Haese]

I've been working on using a TS Optical 3" flattener suited for RC's Getting the right spacing has proven to be a pain. I hope that TS have given me the right spacing this time.

[Logieberra]

Paul, I found your flattener post: http://www.iceinspace.com.au/forum/showthread.php?t=125409

If you're having to buy multiple PreciseParts adapters - I feel for you. They cost a fortune! I hope TS compensates you in some fashion, for the incorrect spacing advertised...

[Paul Haese]

After testing last night I can confirm that the spacing is still a little off. It is certainly better than it was but it is still not 100%. I have attached crops at 100% of the corners. Not a lot in it but enough to irk me. I have requested a response from TS Optical. So far I have had two adapters for this part of the imaging train. Though that is nothing compared to the 6 adapters I have had made up for the rest of the train because GSO don't have specs on their back focus from the back plate. I had to request back focus specs but got ones from the sagitta of the mirror. Not very useful. I think Ashley from Precise Parts loves it every time I order yet another adapter. :eyepop:

[Howie Glatter]

Paul Haese said: "The Glatter one is not going to work for you at all and gives inconclusive results."

Can you detail why ?

[Paul Haese]

In all the tests I have done with the laser and adapter for making concentric circles I have noted that little if any difference could be seen in the concentric rings and yet the collimation would be wildly out from the results using a Takahashi collimation scope. I followed your instructions to the letter and I got the same result each time.

Now I am happy to have it wrong and use the collimator rather than it become a counter weight and would welcome any tips you might have on how to get a very accurate result. I need to warn you, I am really a stickler when it comes to collimation.

In the end this is only my opinion, and I have found that using a Takahashi scope works best at solving collimation on these scopes. And then a final tweak on a out of focus star.

[gregbradley]

Sounds like you need a variable length adapter and then you fine tune it by trial and error.

I think there are some like this stock from some suppliers but Ashley may be able to make a variable one that suits your setup. If it has a range of say 20mm you should be able to nail it.

If its getting better as you go shorter then I suppose you need to go even shorter.

Of course you are assuming the corrector works perfectly at a certain distance. We aren't talking Takahashi, AP or APM quality here so there is a chance the corrector is not up to the job. Full frame is pretty demanding on the optics in my experience. But if changing the distance is getting an improvement then the variable approach is the way to go (2 adapters one that slides into the other and can be locked down).

Looking at your corners at an educated guess that looks like more than 3mm error in the spacing. More like 5-10mm.

What percentage did it change when you reduced the spacing by 3mm?

Greg.

[Paul Haese]

TS Optical did some measurements and came up with the last back focus length. Apparently some optical tech said it would be right this time.

You could be right about it being more. The improvement over the field has been about 94% looking corrected rather than about 50%.

You could be right, the flattener might not be up to what is being stated on their website but I have seen an image taken with a STL11K and this flattener on a GSO RC12 and it looked really good.

Yes a sliding adapter might be ok, but I have put the ball in their court for the moment and I have an acceptable level of correction at present.

I am with you 100% about sensor size. This camera is not for this scope long term, but now this scope has to fill my wants.

[Logieberra]

With the RCOS guys swearing by the Tak Collimation Scope, I didn't think to look elsewhere. Where I have found the Glatter comes in handy (I borrow a mate's on occasion), is aligning the focuser to the factory applied seconday 'spot'. The small laser 'dot' of the Glatter works well there.

[gregbradley]

If you can see examples where it is fully corrected then that gives you confidence it can be done.

Funnily with my experience in flatteners they have not been this sensitive to a few mm being exact. But that's with refractors and so its a different optical configuration.

If you got 94% it sounds like a few more mm should do it.

I presume you are confident the focus is spot on as I do notice with sensitive spacing correctors the stars can look off and then when you are in focus the stars all come good.

Did you allow to add 1mm for the filters and 1mm for the CCD window to the backfocus to get optical back focus as per the Astrodon site advice?

Greg.

[Eden]

I'm looking at a GSO truss as my next purchase. I'd expect that it would need collimation after purchase but ~$300USD for a Takahashi collimation scope is laughable. Are you suggesting that the many GSO truss owners out there who opted not to collimate with said scope haven't done a good job?

[Paul Haese]

Focus is with focusmax at HFD so it is about as close to perfect as you can get and you have seen my images with this scope. Though I take your point being slightly out of focus will present differing results for both the corners and centre of image.

Yes I allowed for the optical effect. Though it should not be as finicky to get it within 12%. My experience has been about 12-16% has the appearance of being flat. So 1mm for filters is not really going to make a huge impact. Right now I would be happy with 16% curvature.

[Logieberra]

Try $232.00 Australian?

http://www.astronomy-electronics-centre.com.au/prices_tak.htm

[Paul Haese]

No not laughable. It is a tool for collimation. And it makes the process fast and easy. You will use it a fair bit and I have used it to help others out too.

I can tell you that a set of mirrors will move in transit. I went to a mates observatory recently to collimate a 10" truss RC. It went out of the box and straight onto the mount. I was there a week later and he had not touched it. It was badly out of collimation. Not the easy part of the secondary, but the primary. An hour later is was in collimation and ready to image.

I doubt many people could collimate the primary of these scopes just by a star test. In fact I would be surprised if that could even be done. The margin for error is very very small.

So don't take it personally. I am not trying to say people cannot collimate the scope. Its just the degree of miscollimation that will be accepted in the end. I have done a lot of high resolution imaging and I know thing or two about collimation now. I am just trying to save people some grief.

[loc46south]

I must support Paul on this one - In the short time I owned a 12" GSO R/C Truss I found it invaluable for collimating the telescope - once mastered it is a quick and efficient way of performing the task.

Cheers
Geof Wingham