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Old 20-06-2019, 05:59 PM
MarcSchafer (Marc)
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collimation of Ritchey Chretien telescope

I struggle to collimate my 8" RC accurately enough for my astrophotography. I cannot seem to find consistent focus across my image (see attached image of the Lagoon nebula) and wondered whether anyone out there can give me some advice. My RC scope only has collimation adjustment screws for the secondary mirror and the focuser column. There is no facility to collimate the primary mirror. I would have thought that this would simplify the collimation process - but not much success yet. Thank you in anticipation.
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  #2  
Old 20-06-2019, 06:30 PM
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Marc,

collimation of an RC is quite tricky but helped with the right equipment.

The first thing you want to do is centre the focuser with the centre spot on the secondary mirror. Use a laser to do this, it must be very accurate and you will need a tilt adjust for this scope. Bintel sell them if you don't have one already.

Once you have that right you will need to align the secondary and primary mirrors. This is best done with a takahashi collimation scope in my opinion. You might like to borrow one from someone but if you want to use an RC long term you will need one, so it is worth buying one. I have attached a reflection map for you to work out what goes where. It will take a little while to work out what reflection is where and what to move, but once you have the hang of it the collimation is relatively simple to undertake. Tweaking the collimation with a star test is the final part of it and it is only done with the primary mirror adjustment screws.

B is the secondary mirror centre spot.

Hope that helps.
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Old 20-06-2019, 09:55 PM
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Have a look at this thread, I found it very useful.
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Old 21-06-2019, 01:12 AM
MarcSchafer (Marc)
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Thank you so much Luka and Paul.
Will definitely follow your advice.
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Old 21-06-2019, 09:50 AM
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This post from glend 2 weeks ago may be helpful to you.

"" As someone that has spent far too many hours peering into a TAK scope attached to a GSO RC, this new device being offered by Teleskop-express may save new RC owners a few grey hairs, and lower your blood pressure.

https://www.teleskop-express.de/shop...skoptypen.html


I like the fact that this thing has LEDs, and does not involve spending more than your budget RC is worth on the tools (be it TAK scope and adaptor, Hotech, etc).

Note it is not available to ship until July. Good luck and let me know how you go with it, as I might be tempted to buy another RC if it works as advertised. ""
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Old 21-06-2019, 05:53 PM
MarcSchafer (Marc)
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Thank you for that Bill.
Sounds like just the instrument that I am looking for.
Am now trying to source some reviews from RC users.
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Old 22-06-2019, 04:51 AM
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Quote:
Originally Posted by Paul Haese View Post
Marc,

collimation of an RC is quite tricky but helped with the right equipment.

The first thing you want to do is centre the focuser with the centre spot on the secondary mirror. Use a laser to do this, it must be very accurate and you will need a tilt adjust for this scope. Bintel sell them if you don't have one already.

Once you have that right you will need to align the secondary and primary mirrors. This is best done with a takahashi collimation scope in my opinion. You might like to borrow one from someone but if you want to use an RC long term you will need one, so it is worth buying one. I have attached a reflection map for you to work out what goes where. It will take a little while to work out what reflection is where and what to move, but once you have the hang of it the collimation is relatively simple to undertake. Tweaking the collimation with a star test is the final part of it and it is only done with the primary mirror adjustment screws.

B is the secondary mirror centre spot.

Hope that helps.
Hi,

Interesting thread. As I also have a scope like that and want to colliamte it in future I have taken a look into it and have seen I have NO donut on the secondary.



What do I do now ? How can I put a donut on the secondary ?

Thanks Rainer
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Old 22-06-2019, 04:55 AM
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Quote:
Originally Posted by billdan View Post
This post from glend 2 weeks ago may be helpful to you.

"" As someone that has spent far too many hours peering into a TAK scope attached to a GSO RC, this new device being offered by Teleskop-express may save new RC owners a few grey hairs, and lower your blood pressure.

https://www.teleskop-express.de/shop...skoptypen.html


I like the fact that this thing has LEDs, and does not involve spending more than your budget RC is worth on the tools (be it TAK scope and adaptor, Hotech, etc).

Note it is not available to ship until July. Good luck and let me know how you go with it, as I might be tempted to buy another RC if it works as advertised. ""
Hi,

Your link to teleskop-express.de link does not show anything ?

regards Rainer
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Old 22-06-2019, 12:03 PM
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That was strange, when I copied Glens post it must have corrupted the link. Try this it works.

https://www.teleskop-express.de/shop...skoptypen.html
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Old 23-06-2019, 02:49 AM
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Quote:
Originally Posted by billdan View Post
That was strange, when I copied Glens post it must have corrupted the link. Try this it works.

https://www.teleskop-express.de/shop...skoptypen.html
Thank you very much. Now it worked

Rainer
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Old 25-06-2019, 01:45 PM
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DiscoDuck (Paul)
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Another useful technique to have up your sleeve is the "hall of mirrors".
It's described part way down this page
https://www.davidcortner.com/slowblog/20110815c.php

Essentially if you look down the tube at the right angle you can see an infinite set of reflections. Line them up behind a spider vane and you'll see them curving off to one side or the other if the primary and secondary mirrors aren't aligned.

I found it useful to iterate this technique to adjust the secondary with use of a laser for adjusting the primary (esp. the Glatter with the holographic circles attachment).

This gets it close enough that a minor tweak with a star test should be all that's needed.
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