Ritchey-Chretien collimation

[Karlzburg (Karl)]

Hi all,

I'm going to do a write up for collimating a Ritchey-Chretien telescope, as you know they can be a beast to deal with ( a phrase taken from a convo today, thanks Alex)

I've read the net and watched the youtubes none have given anything of much use or explanation, I will be putting up pictures as well.
I've tried quite a few different ways shown on other forums and blogs with no real success, I'm mechanical minded and excellent problem solving skills to work out the issues behind doing them.

Cheers
Karl

[DJT (David)]

Hi KarlAre you doing the write up because you have figured out how to do it? Sounds like not?

[Karlzburg (Karl)]

Yes I am doing the write up as I have worked it out.

[Stonius (Markus)]

Look forward to reading it :-)

[DJT (David)]

Originally Posted by stonius

look forward to reading it :-)

Likewise!

[pmrid (Peter)]

You can be certain of a wide audience when you do release this write-up.

The part which I would hope to see included is that dealing with collimating the primary. I have committed the cardinal sin of adjusting my GSO RC8 primary mirror - out of frustration combined with ignorance.

Currently I am working with a borrowed Tak collimating scope (thanks Rick) and believe I have managed to get it just about right. I've tried that method, the "hall of mirrors" method, a Howie Glatter projection system and others and none have been very satisfactory. No doubt this is a case of a poor tradesman blaming his tools. All of this is why I await your work with truly bated breath.

Peter

[ChrisV (Chris)]

Jeez and I thought a newt was hard to collimate. It'll certainly provoked some discussion Karl

[Karlzburg (Karl)]

Newts are a walk in the park compared to RC's. Though very fiddly and a cause for another couple of greys.
I haven't used a Tak scope, it's all been Howie with circle work.
I have my focuser squared with my secondary through full rotation of the focuser, I noticed that if I did move the focuser to allow a few more stars into a shot it there collimation off as it was set at one position, which made me think even moving the camera alone would still put one side off. So sharp stars across the sensor would be gone.

Hoping to have a clear night tonight for a star test.

[Karlzburg (Karl)]

Adjusting primary will be in it too Peter as it's one part of 3. Feom what I can work out it's like the final fine adjustment to the lot.

[Marke (Mark)]

Originally Posted by Karlzburg

Adjusting primary will be in it too Peter as it's one part of 3. Feom what I can work out it's like the final fine adjustment to the lot.

Thats correct after everything else is in alignment you finish with primary adjustment

[John K]

Also looking forward to this! About time someone from IIS took the lead on this as there are lots of CDK/RC scopes out now with forum members.

[Karlzburg (Karl)]

I've noticed quite a few for sale lately and wondered if it was due to poor collimating? Like most things these days it's easier to get rid of and get something different than fix what you have. Very much a throw away society this day and age.

[Stonius (Markus)]

I think it's the gnawing uncertainty - could it be better? Was it the seeing or my collimation? That kills people in the end, even if they're getting quite reasonable FWHM's

[glend (Glen)]

Originally Posted by John K

Also looking forward to this! About time someone from IIS took the lead on this as there are lots of CDK/RC scopes out now with forum members.

Just about all the RC collimation drama threads have to do with the nightmare that are the GSO made small models 6"-10", which are the budget end of all RCs. I have never heard any complaints about Planewave RCs.
Perhaps the write up should be GSO specific.
Good luck.

[Stonius (Markus)]

True, but ppl who can afford a planewave are probably more experienced

[RickS (Rick)]

Planewave scopes aren't Ritchey–Chrétien. They are a corrected Dall-Kirkham. The difference is that the CDK has a spherical secondary and it doesn't matter if it isn't perfectly centred. This makes them somewhat easier to collimate.

Cheers,
Rick.

[glend (Glen)]

Originally Posted by RickS

Planewave scopes aren't Ritchey–Chrétien. They are a corrected Dall-Kirkham. The difference is that the CDK has a spherical secondary and it doesn't matter if it isn't perfectly centred. This makes them somewhat easier to collimate.

Cheers,
Rick.

Ok thanks. So the next question is, who, besides GSO makes RCs for the amateur market?

[RickS (Rick)]

Originally Posted by glend

Ok thanks. So the next question is, who, besides GSO makes RCs for the amateur market?

There are some high end suppliers like Alluna and Officina Stellare. GSO is the only low-cost vendor that I know of.

[Marke (Mark)]

There is a huge leap from GSO to anything else but I think WO are working on something I have seen a 14" they did with a 12" on the way I believe.

[DJT (David)]

Hi GlenThere is a huge gap between GSO and the other manufacturers who are all pretty much in same price range, around the 10k plus mark. As I understand it, the complexity is in the mirrors? But the cost ramps up as other materials are used along with better mechanical design.


There are no other non clone manufactures doing 8 inch mirrors from what I can see and that is the sweet spot for a lot of amateurs mounts. CFF has a 10” but that’s still going to cost 10k landed, 3x the cost of the GSO RC10 and would stretch most mounts capacity.


so whilst mechanically the GSO is a bit needy, there are plenty of astrophotographers out there using them successfully. Kudos to GSO for coming up with a way to produce the mirrors so they are affordable and quite good.


Fabiomax posted up a couple of really great images recently and he has the budget RC8 with QSI CCD setup.


Very much looking to see a simple Collimation write up. But I still think dropping $1500 for a decent focuser, t-ring and tak scope is well worth it for the images you can get from these scopes given focal length.