Collimation for GSO RC10 - need help

[lazjen]

I've done a lot of searches and read a few guides, but I'm unsure what's the best way to sort out the collimation mess that my GSO RC10 (CF version) is in right now (I seem to be getting stars that look like comets).

For those that have this scope or have used it, what do I need to get/use to sort this out properly?

[glend]

Patience and a sense of humour, and a Tak collimation scope.

[jwoody]

Hello Chris
I have a RC10 also and use the Tak collimation scope with success. I have read others have success with howie glatters and such but I think the Tak scope is the most common tool.
If you are ever down Gold Coast way bring your scope to my place and we can get it sorted out.
Jeremy

[lazjen]

Given how long it's taken to get (back) to where I am now, I think I can managed some more patience. :)

Looks like I'll be buying a Tak Collimation Scope in the near future.



Jeremy, thanks for the offer. I may take you up on that if I can't work out what to do. I think that the Tak scope is the most feasible way to go as it looks like I can actually buy one.

====

On a different path - I was reading that I should only be adjusting the secondary mirror. How can I tell that the primary mirror is not an issue?

Chris

[glend]

Chris if you bought it new then the primary should be pretty good, as they are setup in the factory. The problem comes with used scopes where people who Don't know any better try to collimate them like newts. Once that primary has been moved you could be in a world of trouble. Unfortunately that is when folks tend to sell them on to someone else.

Imho, Just follow the standard GSO RC approach, centre your focuser to the secondary centre spot first. Get the optional collimation ring from Andrews if you don't have one, it allows you to adjust the aim of your standard laser inserted into the focuser. Then concentrate on the TAK collimation scope view to get the secondary correct to show equidistant ring alignment.

[lazjen]

I did buy it new a few years ago and I've obviously never touched it before. I'll follow the normal approach and see what happens.

I got a PM that mentioned that I should get the collimation ring as well, so I will do that too.

[lazjen]

I've got the tilt plate for collimation. How do I determine the tilt from the focuser? I am assuming the circle from the tak scope shouldn't appear to move when the focuser is rotated?

[brisen]

Hi Chris

You will need to use a laser to centre the focused onto the secondary. Use the adjusters on the tilt ring to get the laser centred on the secondary. Then use the task scope to get the collimation right.

Brian

[glend]

Well the way I did it was to use my laser collimator in the focuser, you want it to hit the centre spot on the secondary precisely. Then the TAK scops after that. Where you place the Collimation ring in the spacer train is important, don't put it up front where it will block the primary adjusters.

[lazjen]

Ok laser beam it is. Will have to sort something out for that.

[glend]

Look that is just a suggestion based on how I did it others might chime in too. It maybe very possible to do it all with a TAK Scope.

[lazjen]

Maybe, but I think getting the tilt sorted will be easier by other means.

I was informed about this: https://www.rafcamera.com/adapter-m117x1f-to-m36-4x1f-to-m48x0-75m. Looks like I can get an adapter to take the focuser out of the equation. Might get it.

I can then deal with the focuser tilt as a separate issue - which will probably still need some form of laser to sort out efficiently. If I could be 100% certain that the collimation is correct, then the tilt could be sorted out by taking images and analysing the results in PI (which I will do at least as a final check anyway).

[lazjen]

An update.

I got the adapter above and eliminated the focuser from the collimation process since I was able to directly attach the tak scope to the RC10. The semi-good news though is that the focuser appears to be well collimated anyway as there was no visible change to what I could see. :)

I tried to do a collimation without touching the primary mirror, however I couldn't get the dot in the secondary to line up properly (within the little circle of the tak scope). I made some adjustments to get the larger circles aligned nicely (expecting though it wasn't going to work).

I then looked at the results under the stars. Out of focus the stars looked mostly ok, but when I moved close to focus it was quite obviously wrong - they looked like they had 'v' shaped wings (like a winged viking helmet).

It's at this point I made things worse.

I tried to adjust the spider vanes on the secondary to see if I could get the secondary lined up - no go, they're basically locked in place. I then unscrewed the secondary from the spider to examine the system further. While it gave me a greater understanding of how the push/pull system worked, I couldn't see any obvious mechanism there that would help with aligning the secondary dot to the primary.

I put the secondary back on and adjusted the collimation as best as I could. However, when I went to do a star test - couldn't find stars or get focus. At this point I realised I had severely messed up the distance between the secondary and primary mirror and had probably reduced the focus to somewhere I could now not reach.

Ok, time to find out what distance to set the secondary (the push/pull screws) and/or find out the distance between secondary and primary. Googling away hasn't given me any details though. I have found figures I think for RC12 and RC8, but not RC10.

Anyone know the figures required? If anyone has a GSO RC10 (closed tube if it matters - I've got a CF) that have a collimated scope and could measure these values, that would be great.

Back on the secondary dot and adjusting it to align - I'm open to suggestions on this as well. I'm going to see if I can get a laser to check that the dot is really the centre if I can determine a way to attach it without potential tilt.

[Star Catcher]

yes. It is:

Mirror Separation -----463.64mm


Ted

[lazjen]

Thanks. That's a very specific number. How precise do I need to be?

[Star Catcher]

You need to get as close as possible. Otherwise even with perfect collimation, you will not have good stars shapes.

From my recollection, I used one of those telescopic pointers. Like those you used to see on radios.

I set its length as close as possible to the separation distance and stuck down each segment with gaffer tape so the distance would not change. It is then possible to get your hand into the tube space and very gently test the separation. Then use the centre bolt in the secondary holder to either shorten or length the distance.

I am sure there are more elegant ways to do it but that is what I did :)

Ted

[lazjen]

I got an old broom handle and marked off the length and put some soft tape over the end to protect the mirror. Then I inserted it from the back to check the distance. I think I'm close. I can probably iterate from here with star tests,

On the issue of the secondary marker: with the use of a laser I think I've worked out that the secondary marker circle is very slightly off centre. With the focuser removed, I got the laser attached using the same adapter for the tak scope. I could see the laser form a point back on itself.

When I put the focuser back on, and attached the laser, and then rotated the focuser, it made a small circle around the mid point. I think I need to collimate my Moonlite focuser. I'm going to send off a message to find out how, since a video showing what to do has bits that mine does not seem to have. I should point out that before I put the focuser on, I made the collimation as good as I could get with the tak scope.

At this point, I'm not sure if I can properly test the system since the focuser is not correct.

[Star Catcher]

It should not scribe a circle. You cannot collimate it in that condition. There are a few videos which you have probably already checked and was not happy with.

https://www.youtube.com/watch?v=DWMQh6OvpJc

https://www.youtube.com/watch?v=Mw4hIq_byp4

[lazjen]

Right. I did the collimation of the scope without the focuser. I have the attachment to directly connect the tak scope to the back of the RC10, so the focuser can't interfere. I dislike having multiple variables to deal with at one time.

I saw one of those videos - my unit doesn't seem to have the adjustment points on it (it has for the flange part, but not on the tube). I've sent an email off to Moonlite to ask about it.

[billdan]

Hi Chris,
Before you fiddle with the focuser, just make sure your Laser is colliminated.
Make up a V block and point the Laser at a wall 3 metres away and make sure it doesn't draw a circle when rotated.
I made mine with a 3D printer but you can also make one up with Lego bits.
There should be 3 small collimation screws on the Laser that you can adjust.

This is the procedure I used from a guy on Cloudy Nights or SGL?

Once you have the laser in a static position where it can only rotate, and not slide back and forth in any way then you can rotate it through 360 degrees . Number the laser collimation screws 1, 2 and 3 with a pencil (as this can write on the black tube) and then as you rotate mark the position of the spot on the wall when screw 1 is up, then 2 , then 3. Numbering the dots will help you work out which to adjust and which to slacken.

Next join the dots to form a triangle and then put a spot in the middle of this. Now adjust the screws to move the laser spot onto this. Once again rotate the laser to make the triangle, draw another centre spot and readjust again.
By doing this I managed to get a single spot when rotated within about 10 min’s and three "triangle" cycles.



Cheers
Bill

[lazjen]

It's a moot point anyway for adjusting the collimation of the focuser - it's an old model that doesn't have the option. Ron at Moonlite has offered an upgrade path for it to the newer model that can be adjusted. I have to think about whether it's worth the postage costs involved to send to/from US if I go ahead.

Before I go ahead however, I'm going to go and recheck everything anyway. So I'll check the laser as well using something similar to your suggested test. I did do a test where it was attached to the collimated scope, without the focuser, and I rotated the laser within the compression ring attachment. It did not inscribe a circle, but reflected back on itself. I think this is a valid test, but doubts are creeping in. :)