Altair Astro RC8 - collimation or camera alignment?

[markarian]

Just got an Altair Astro RC8 - seems a really well made bit of kit.

First image with it (bubble nebula) shows star trails on the right hand side of the image only though. Is this likely to be bad collimation or alignment of the camera in the focuser? Any ideas?

RC8 f/8, Canon 350D modified, 10x180s, 7x240s, Astronomik CLS, darks, flats, ISO 800, guided

Thanks

Mark

[kookoo_gr]

i would go for bad alignment of the camera due to fact that the factory focuser can't be properly level when placed at the extensions or the scope itself. if you remove the focuser you will notice that at its base there is a V edge (don't know how else to call it) this V shape allows the focuser to move at an an angle when you screw it in the telescope. The solution in my opinion is to buy a better focuser, i bought a moonlite that doesn't have this V shape edge at its bottom and the focuser can sit level at the scope. if you can't afford for the time being a new focuser here is a method i used in order to place the focuser as level as possible at the scope.

1.first place the scope without the focuser (you can place the extensions you have at the scope) at a level table or bench (make sure the table/bench is level), you must place the scope vertical to the ground without its protective cap.

2. put the focuser at the extensions/scope but don't tighten it yet

3. place a film canister at the 1.25'' adaptor, just like as you would collimate the scope

4. place a bubble level on top of the film canister (http://astroadventures.files.wordpress.com/2010/06/level.jpg)

5. while tightening the focuser make sure that the bubble of the bubble level remains at its center

6. when finished the focuser should be as best as possible in the center of the optical path

this method doesn't eliminate this problem but you should be able to improve things, also when imaging make sure after 20 mins to check the focus since it has a habbit of loosing it every 20-30 mins

finally you can check your collimation using this method

http://deepspaceplace.com/gso8rccollimate.php

[r3i]

Looks like it could be a tilt in the image plane. Would suggest checking the following:

• Check the camera is seated squarely into the focuser - I find it easier to have the focuser sat vertically on a bench, then fit the camera into the focuser before attaching both to the scope.
  
• Once you've achieved focus ensure the focus lock is nice and tight: there's the potential for some flexure here.
  
• Check that the 3 lock screws on the primary collimation are also as tight as possible as this is another location where flexure can occur.
  

[markarian]

Thanks for the advice guys. I will give your ideas a go and let you know how I get on.

Cheers

Mark

[markarian]

Got much better alignment last night. Used a combination of your ideas guys - but basically attaching the camera/focuser when the tube is vertical makes the difference. There is still some slight trailing around the edges but that's probably because I'm not using a field flattener. Guiding wasn't so good either because of gusty winds.

Thanks for your help. Probably still some more improvements to be made but quite happy so far.

Regards

Mark

[ollypenrice]

I think Altair Astro are offering a camera tilt adjuster...

Olly

[r3i]

Got much better alignment last night. Used a combination of your ideas guys - but basically attaching the camera/focuser when the tube is vertical makes the difference.

Glad to hear you're getting sorted - that mis-alignment of fitting the camera into the focuser has caught me out a couple of times - I wish there was some screw thread based method of attaching the camera to the scope thus eliminating the 2" slide in fitting.

I think Altair Astro are offering a camera tilt adjuster...

Olly

Can't see them on the Altair site, though that doesn't mean they don't sell them. There's a few offerings that I know of in this area which may be interest:

• Optec Equuleus - bit pricey
  
• Gerd Neumann CTU - similar to the Optec but cheaper
  
• TS Focus Collimation TSRCJ90 - Specific to the GSO 6" & 8" scopes
  

[markarian]

I think Altair Astro are offering a camera tilt adjuster...

I had heard that somewhere Olly - they must think there is a need for something.

Glad to hear you're getting sorted - that mis-alignment of fitting the camera into the focuser has caught me out a couple of times - I wish there was some screw thread based method of attaching the camera to the scope thus eliminating the 2" slide in fitting.

Yes - I was hoping for a T-thread on the end of the focuser too. Would certainly help,

I was caught out with camera misalignment on my 200P too. That was sorted by using a compression ring fitting - but this focuser already has one. I wonder if 3 screws rather than 2 would help?

Can't see them on the Altair site, though that doesn't mean they don't sell them. There's a few offerings that I know of in this area which may be interest:

• Optec Equuleus - bit pricey
  
• Gerd Neumann CTU - similar to the Optec but cheaper
  
• TS Focus Collimation TSRCJ90 - Specific to the GSO 6" & 8" scopes
  

Hope I can do without spending extra but it may come to that. Thanks for the info.

Do you use one of these?

Mark

[r3i]

Hope I can do without spending extra but it may come to that. Thanks for the info.

I have the TSRCJ90 one - I had a problem with the chip in my QHY8 being tilted, so I bought the TSRCJ90 as a possible solution. However I dismantled the camera and have been able to square up the chip. Since doing the remedial work I've not done much imaging to check if the fixes have worked due to moving house, but hoping to get back in the saddle soon.

If I do find that I still need to make tilt adjustments, I'll probably look at getting one of the Gerd Neumann devices as the TSRCJ90 would only work with the RC and I'd like to have a solution that would also work when doing wide field imaging through my 70mm frac.

[ollypenrice]

Tilt is a fairly well known problem. Atik seem to get it right at the factory and SX make their chip tiltable in camera. QHY are very prone to being tilted as appears on plenty of threads but these adjusters are a great idea if they work OK. I've never seen one myself.

Olly