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Old 04-06-2020, 07:38 PM
boofhead78 (Peter)
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collimation of 8 inch rc frustration

howdy all!

this is my first post on ice in space. I've got an 8 inch gso rc, and it's been out of collimation for over a year now. every time I think I'm about to get the technique right, it seems I need more accessories. the equipment I have to do this now includes a Takahashi collimating scope, a howie-glatter laser, and a tilt adjuster on the focuser .

I would like to be able to collimate my scope inside so as not to waste precious photo time. I understand that when I shine my laser through the eyepiece and towards the wall in front of the scope, that I should see concentric rings. instead I only see a single large red ring, despite racking the focus in and out.

I reckon I can collimate my scope if I could see some rings, but only see the one

hoping for some good simple advice please!
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Old 05-06-2020, 11:19 AM
Emc2 (Jon)
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Peter, do you have a shiny metal ball - ball bearing type - lying around?
If you do, simply place it in the sun 25m or so away from your scope. You can then use this as an artificial star for collimation. You'll see an airy disk and rings in and out of focus.
Alternatively you could purchase an artificial star generator, but that's just one more bit of equipment.
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Old 05-06-2020, 11:32 AM
boofhead78 (Peter)
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hey Jon !

thank you for your advice ! I did buy an artificial star light, but have no idea how to use it. I live in a block of apartments and so don't have much room in which to fix my scope
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Old 05-06-2020, 12:21 PM
Emc2 (Jon)
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An artificial star basically reproduces the pinpoint nature of a star. You'll need some good distance between it and your scope, perhaps you can try it in your hallway or something.
Can be done outside too of course if you are willing to bring your gear down and setup outside.
Same concept as the ball bearing: just place it away from the scope: I would say at least 20m away. Point to it, find it in your eyepiece and you will then see the rings on each side of the focus and the airy disk if the conditions are right.

Just take your time in adjusting the collimation, not something to be rushed.

Here is a great article detailing the procedure:

http://www.astrophoto.fr/collim.html

Hope this helps!
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Old 05-06-2020, 12:32 PM
boofhead78 (Peter)
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thank you so much ! I'll have to give it a go when I get some time. those distances aren't something I can do at my place . will have to give it a go at someone else's place, but it's good to know I was too close at my place - 3-4 meters max!
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Old 05-06-2020, 12:43 PM
Emc2 (Jon)
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no problems - yeah you do need a bit of room for this, but again you can also setup outside if there is a bit of lawn or shared common property. Good luck with it all!
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Old 05-06-2020, 01:15 PM
glend (Glen)
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Peter, I am a former RC08 owner, and collimation of the RCs can be very tricky. Personally i wpuld not obsess about focuser tilt, it is not the main issue. The interplay of the two hyperbolic mirrors are where people get into trouble. I suggest you read some of the many RC collimation threads, like this one:

https://www.cloudynights.com/topic/6...2#entry9140153

BTW, if you have a TAK Collimation scope that should be all you need, but a bright surface and light into the TAK scope is very important.
Always adjust the secondary first, try not to touch the primary if you can, because then you have to adjust the secondary again, and on it goes. RCs are both really beginner scopes because of the collination sensitivity.
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Old 07-06-2020, 12:52 AM
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luka
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Peter, see this thread. The link with the manual is broken but you can find an updated version here.
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