GSO 12" RC Dissambly.

[Jussi_K]

And one more.

[kirkster501]

Spectacular!

Sent from my iPhone using Tapatalk

[kirkster501]

What i have found with the RC8 scopes is that the focus changes very slightly through the imaging run.  Whether this is expansion of the tube or just focuser drift I don't know. Maybe I am too used to the FSQ where you focus and leave running all night.  This is not the case with the RC8 I have - it needs a refocus when changing filters for sure.

[Rockenrock]

Hi Rob,

I have reading with great interest your, Doug007’s and Marco’s writings about the primary mirror mounting problems. Your solution for your truss unit was to make the focuser mount to the rear cell with your new coupling. Directly mounting the focuser makes sense, but how did you decouple the mirror from the image train? Does it simply hang off the 3 collimation screws? If you have any additional pictures or sketches of your design you can post, I would appreciate seeing them. I am not looking to copy it, but don’t want to re-invent the wheel, when you already carved one.

You mentioned about a new multi point mirror cell you were having made in France. Was that the final thing that made you happy with your RC12? Are you still using your RC12? My 10" mirror is much lighter, and I do not expect that will need a new cell.

I have the 10RC carbon, and can see the Glatter laser point move around on the secondary as I load and unload (by hanging weights) the weight of the image train on the body (not drawtube) of the Moonlite focuser. That means collimation changing depending on direction OTA is pointing.

Thanks!

 Roger

 in Hong Kong

[Rockenrock]

Hi Rob and others;

I have to admit, I am now can self-classify myself as a tinkerer, trying to learn and improve my AP setup...

Motivated by all the above discussions (and your blissful tinkering  ) on the collimation, mounting, and mechanical problems of the GSO 12" RC and 10" RC, I started my tear-down and study my GSO 10" RC fiber these last 3 weeks. My goal was to understand the design from a mechanical perspective, the fallacies  of GSO design, and how to fix it. As others have mentioned, the image train weight makes the primary point in different directions (slightly) depending pointing elevation. So what elevation is best for collimation? Well, I don't want to worry about that. I decided the mirror mounting if decoupled from the image train, was pretty well fixed and no undue forces on the mirror. My 10" mirror cell does not have the 3 outer clamps seen on the 12". This left the decoupling as the change needed.

Since the OTA was now apart, I decided it was best to have a good 3D CAD file made for the overall construction. Then I could design  an isolator to decouple the image train. (Will attach picture from CAD). The Isolator (my term) bolts directly to the back plate with 6pcs M6 cap bolt. Internally the diameters go around the threaded end of the primary mirror cell flange and then steps inward to the same diameter and male threads of the GSO supplied focuser tube extensions. I left the 60deg conical on the inside in case I every want to play with the GSO focuser on it instead of my (still in the box) Moonlite CSL focuser with 68mm threaded drawtube.  

Since Hong Kong weather is pretty cloudy, I have to do as much inside as possible. So here is my plan for alignment before star testing:

1. Reassemble the OTA (I took it apart to make the 3D CAD) with Moonlite focuser, but leave off the entire secondary assembly and spider vanes.

2. "Collimate" focuser: Install the Howie Glatter laser to the 2" to 68mm adapter, and point the beam through OTA at the wall 30ft away. Check and adjust the focuser collimation by turning the rotary flange of focuser and adjust until beam movement is minimized (I think fit in 1/4" dia circle can be achieved)

3.  Install secondary assembly, turn on laser, and adjust the new Isolator (using shims) until the laser hits the center of the secondary.

The above makes the focuser in alignment with center of secondary.

4. Remove secondary assembly from tube (mark angular position to tube first), set up a point light source (maybe use a shiny ball bearing reflection) and move it around until it is at the focal point of the primary mirror. This should be the optical center line of the primary. I have never done this. Any advice on finding the optical centerline of primary?  Thanks! Can the light source be slightly off axis with something put at the center of the reflected light beam?

5. Then turn on the laser (which points along desired optical center to secondary), and adjust the primary mirror collimation until the laser points directly at the point light source which is on the optical centerline. I hope within 1/16 circle.

6. Re-assemble the secondary assembly using the mark for correct screw location.

Now I think ready to star test for final tweaks.

I would appreciate your review and advice on the new Isolator part, and the indoor collimation steps.

Thanks!

    Roger

GSO 10" RC on G11-Gemini 2 on custom pier, bolted to concrete roof in Hong Kong

Moonlite CSL, AO8T, FW8G-STT, STT8300M

[Rockenrock]

Here is the cut-away section I promised!

[rpineau]

I want one !!!

Seriously if that can be made into a commercial product, every AT10RC and AT12RC owner will buy one (and may be make a smaller one for the smaller AT RCs).

Rodolphe

[Rockenrock]

Rodolphe,

The Isolator part is easy enough for any adapter maker to crank out.  

Installation then requires drilling and tapping 6 holes in back plate using 6 holes in the Isolator part as starting guides. Some skill need to align isolator on center, and then to drill in middle of guide holes. Then the drilling and tapping chips must be cleaned out. How to do this without taking scope apart  ???? So easy is not so easy sometimes. Unless you are a tinkerer!

I have not made the part yet, and still looking for someone to comment more on my design concept and the 'collimation steps' above.

From what I have read, the smaller AT RC's are different construction, so some things must be different.

Thanks,

   Roger

[Zakalwe]

Rodolphe,

The Isolator part is easy enough for any adapter maker to crank out.  

Installation then requires drilling and tapping 6 holes in back plate using 6 holes in the Isolator part as starting guides. Some skill need to align isolator on center, and then to drill in middle of guide holes. Then the drilling and tapping chips must be cleaned out. How to do this without taking scope apart  ???? So easy is not so easy sometimes. Unless you are a tinkerer!

Could you not bond the part to the back plate? A 2-part epoxy adhesive will give huge grip, almost certainly stronger than bolts.

[Rockenrock]

Hi Red Dawn,

I agree a good epoxy bond would be permanent, but you would not know if the Isolator was in line with the secondary until after the bond dried. Then no way to adjust it. The back of the back plate is not a controlled surface. It may or may not be in alignment with the tube and secondary. With bolts, it can be shimmed and adjusted.

Thanks for your creative thoughts!

Roger

[Zakalwe]

Hi Red Dawn,

I agree a good epoxy bond would be permanent, but you would not know if the Isolator was in line with the secondary until after the bond dried. Then no way to adjust it. The back of the back plate is not a controlled surface. It may or may not be in alignment with the tube and secondary. With bolts, it can be shimmed and adjusted.

Thanks for your creative thoughts!

Roger

Good points.

What about making a mounting plate that has studs or tapped holes in it. This could be bonded to the backplate. Slotted holes in the isolator would allow for some movement to line things up. That would save disassembling the OTA to fit it?

[Rockenrock]

Wow, that is great idea. I can make a 4mm or 6mm thick ring with the 6 holes pre-threaded. Then bond it to the back of back plate without modifying the back plate. I am sure I can glue it coaxial to the center of the mirror cell. The only adjustment would be shimming between the Isolator and the ring to get better collimation.  I am going to think on it more.

Good creative problem solving!

Thanks,

    Roger

[rpineau]

@Rockenrock

I totally agree that the scope need to be taken appart and that whoever is installing the adapter need to properly center it (in addition to the drilling and tapping). How to do it might be the added value for a company willing to do this.

I'm not saying it's plug and play, but if some company makes this and offer an install service, I'll definitely would send my AT12RC to get this done (specially if they are not too far ...).

In any case .. this is a very desirable mods for these scopes.

Rodolphe

[Rockenrock]

Here are a few pics of my scope in bits, and the modified rear cell, which the focuser attaches to, rather than the rear of primary.

You can also see the amount the secondary is offcentre by. The laser is dead inline with the centreline of the focuser assembly.

Inside rear assembly.jpg

CENTRE OF SECONDARY OFFSET.jpg

Hi Rob,

I hope you are still following your old post. The entire link of posts here has been very helpful and inspirational to me.

I notice your new adaptor is bolted from inside the rear cell to the outside. You also mentioned the secondary is off center of the secondary. 

I designed and had built a similar adapter which I call Isolator since it isolates the image train from the primary cell. I chose to have my 6 pcs M6 bolts going through the isolator into the rear cell. I'll post a picture later.  

I did not machine the back of my rear cell flat since I did not know what datum would line up (orthogonal) with the secondary. After assembly, my laser dot was off center similar to yours. I spent about an hour collimating the laser dot to the secondary by shimming between the isolator and the rear cell. The shimming moves the entire image train, so the laser stays aligned with the focuser.

The huge improvement we both saw is that the image train is rock solid to the rear cell and secondary. 

Roger

[silentrunning]

I'm having this adapter built which allows for lateral adjustments as well as taking all the weight of the main mirror cell...

[silentrunning]

Here's a better view of the adapter...

[silentrunning]

Well the adapter is back from the manufacturer - Graham at Astrotec who has done a cracking job.

Here's a number of pictures of it....

[Rockenrock]

Hi Doug,

Your adapter is very nicely done. I did not consider the grub screw connection for adjustment with my isolator adapter. I think yours is more user friendly and provides lateral movement. Can you rotate also? Mine does not.  

For alignment  I shimmed between the back plate and my part. I don't expect to have to do it again. Now the next weak link in the image train is the GSO focuser which hangs all the imaging items off that shiny rectangular bar on the bottom of the draw tube. Since it could not handle (slips or could not fine focus upward) my 5-6lb imaging load when pointing up I had to upgrade. 

BTW, I used the Howie Glatter laser to align the centerline of focuser to point directly at the donut on the primary, then adjusted the secondary so it reflects directly back on itself. Next step, when I get clear skies is star collimation to balance the image..

Looking forward for your images using the new setup. 

Clear Skies for you!

   Roger

[silentrunning]

Thanks Roger

The adapter does not allow rotation but that can be done further down the chain of components. The GSO tilt adapter allows for the equivalent of shimming and screws into the new adapter. So I have lateral, rotational and tilt adjustments now possible.

The GSO focuser remains the weak link for me but I have managed to tighten everything up so it works as well as it can for what it is. I have no problem stringing FF/FR, FilterWheel, QHY11, and various over things of the back of it. Still not the best focuser in trhe world!!! I have only got around to daylight aligning at the moment using a standard chesire and everything was so much easier than the previous attempts. I'm looking at borrowing a takahashi collimation scope just to get that center spot bang on. Next step is visual star collimation using the primary screws.

Doug

[gorann]

I just found this thread and have read it with great interest as I may invest in a GSO clone RC12" one day. A lot of impressive thinking, modding and tweaking! I could not see that anyone has commented on the fact that Teleskop Service appears to have read the thread too and is now selling an "Upgrade Kit - focuser and mechanics for 12" and 16" RC telescopes" (at least for the truss tube version). It attaches the focuser to the back plate rather than the mirror cell. The problem with mirror cell support may still remain...

Here is the link:

http://www.teleskop-express.de/shop/product_info.php/info/p6686_TS-Upgrade-Kit---focuser-and-mechanics-for-12--and-16--RC-telescope.html