57 replies to this topic

[Staradventure21]

Hello there. I've been using my Nexstar 4se for three years, and now I'm seriously contemplating to buy a new OTA. I will have an AVX Eq mount really soon, and I'm going to put the OTA on it. So, here's the question: Is it hard to collimate GSO CC6 classical cassegrain? I've heard that it's quite tricky to collimate CC, is it true? If so, how much is difficult to collimate a CC?

[quilty]

It's easier than a Rutten Mak. You can first use the spider vanes to adjust the primary mirror in the HOM (Hall of Mirrors) then adjust the sec. mirror.
Then center and straighten the HOM again then sec. mirror, iteratively. The final tiny tweaks, sec. mirror only, at the true star at high pow.
All the HOMwork before comfortably in daylight.

It's more complicated than an SC but with the help of the spider vanes the primary mirror is fix soon and then it's chidlsplay.
First iterations involve the primary mirror, too until there's a straight concentric HOM. The tiny rest is done at the star. But with the HOMwork done properly you're near perfection already, good enough for any observations, just the star pattern might not be all symmetric.

The good thing is, this CC6 is very stable and it keeps its collimation when you transport it.

Only thing to see to: The primary mirror might be loose then any collimation is pointless.

So in case you're off collimation I'd check that first and fix the ring finger tight. (Unaware of this point collimation once drove me crazy because no screw turn yielded a logical effect but since that mirror fix I didn't need to collimate the scope again)

Edited by quilty, 29 April 2025 - 05:39 AM.

[Staradventure21]

It's easier than a Rutten Mak. You can first use the spider vanes to adjust the primary mirror in the HOM (Hall of Mirrors) then adjust the sec. mirror.
Then center and straighten the HOM again then sec. mirror, iteratively. The final tiny tweaks, sec. mirror only, at the true star at high pow.
All the HOMwork before comfortably in daylight.

It's more complicated than an SC but with the help of the spider vanes the primary mirror is fix soon and then it's chidlsplay.
First iterations involve the primary mirror, too until there's a straight concentric HOM. The tiny rest is done at the star. But with the HOMwork done properly you're near perfection already, good enough for any observations, just the star pattern might not be all symmetric.

The good thing is, this CC6 is very stable and it keeps its collimation when you transport it.

Only thing to see to: The primary mirror might be loose then any collimation is pointless.

So in case you're off collimation I'd check that first and fix the ring finger tight. (Unaware of this point collimation once turned my crazy because no screw turn yielded a logical effect but since that mirror fix I didn't need to collimate the scope again)

Big thanks for your advice. Seems like you had used/or are using a CC. Can I ask one more question? Some says that even if we collimate CC like 99%, the quality of images would not be the same as before, is this true?

[quilty]

no. The CC design is more delicate at good collimation than an SC but as said above when the star pattern is not quite symmetric there's no image degradation noticeable at Jupe or the moon.
It's easy without any collimation tool except wrench (two sizes, or three?) and star. Don't remember what wrench sizes are needed for the primary mirror, (done once lasts forever) the sec. mirror is 4 mm Allen key (quite a different torque from what you might know from SC scopes)

Edited by quilty, 29 April 2025 - 05:28 AM.

[Staradventure21]

no. The CC design is more delicate at good collimation than an SC but as said above when the star pattern is not quite symmetric there's no image degradation noticeable at Jupe or the moon.
It's easy without any collimation tool except wrench (two sizes, or three?) and star. Don't remember what wrench sizes are needed for the primary mirror, (done once lasts forever) the sec. mirror is 4 mm Allen key (quite a different torque from what you might know from SC scopes)

Your advice actually helped me a lot choosing my new OTA. Thank you.

Edited by Staradventure21, 29 April 2025 - 07:45 AM.

[Airship]

I have an RC8, a CC8, and two CC45s (the little 4.5" CC). I also collimated a 6" f/20 and a 20" DK from scratch. I haven't had any problems collimating them. They can get tricky if the alignment of the primary is off, but most of the new RCs and CCs that I have used only required tweaking the secondary, which is the same as collimating an SCT. If on-axis stars show astigmatism, then the primary is off a bit. The overall procedure is to align the secondary and check for on-axis astigmatism. If necessary, make a _tiny_ adjustment to the primary to reduce the astigmatism. Repeat until you converge to a solution. It's not hard, but take a little time and patience. Once done you should never have to do it again.

 

Food for thought.

 

Enjoy!

[Bill Barlow]

When I owned a CC6 a few years ago, I just needed to adjust the secondary alignment a slight amount.  Never touched the primary mirror and wouldn’t recommend it unless it is absolutely necessary.  

[GrassLakeRon]

My CC6 hasn't moved since I bought it.

[quilty]

This may say either that you didn't move it or it didn't move.

It was my most used one since the Skymax6 which now is and the CC doesn't move anymore

[azure1961p]

Can't be more difficult than a C90, pain in the posterior.

 

Pete

[Staradventure21]

Can't be more difficult than a C90, pain in the posterior.

 

Pete

Lol, what a relief! Thanks for very persuasive example

[Staradventure21]

My CC6 hasn't moved since I bought it.

when did you buy your CC?

[Staradventure21]

I have an RC8, a CC8, and two CC45s (the little 4.5" CC). I also collimated a 6" f/20 and a 20" DK from scratch. I haven't had any problems collimating them. They can get tricky if the alignment of the primary is off, but most of the new RCs and CCs that I have used only required tweaking the secondary, which is the same as collimating an SCT. If on-axis stars show astigmatism, then the primary is off a bit. The overall procedure is to align the secondary and check for on-axis astigmatism. If necessary, make a _tiny_ adjustment to the primary to reduce the astigmatism. Repeat until you converge to a solution. It's not hard, but take a little time and patience. Once done you should never have to do it again.

 

Food for thought.

 

Enjoy!

Thank for advising me. 

[Staradventure21]

I'm also considering to buy an SCT 6", C6 xlt if a CC is not suitable for my goal. I want to image of course planets, and lunar-- and small DSO's like planetary nebulae, clusters and maybe a small galaxies and bright galaxies. I think CC provides well detailed view of objects due to its special optical design, and also a nice performance in imaging. So CC's kind of attractive to me. Compared to C6, what's good about CC6? I'd like to inform you guys that, my budget is quite limited. 

[quilty]

Yes the CC6 is more of a scope for the money that any other except Newts.
My best purchases however were second hand. The Skymax6 I got last autumn for 200€, and it outperforms the CC6 optically.
Though at imaging I think the CC is preferable due to its larger illuminated field. And the focusser is not too enjoyable but it can be locked for imaging.
(It can't move or lift more than one pound so at long term I think a better focusser is necessary.) Visually I prefer the Skymax' mirror focusser

Larger illuminated and better corrected field than the C6, too


Funny though, all starters try with new stuff, me too. why don't they try second hand first? Like at horse riding, car driving...
Like my wristwatches, my first one was purchased new, then I found out the most beautiful specimen were made in the 60ies

Edited by quilty, 30 April 2025 - 02:32 AM.

[Staradventure21]

no. The CC design is more delicate at good collimation than an SC but as said above when the star pattern is not quite symmetric there's no image degradation noticeable at Jupe or the moon.
It's easy without any collimation tool except wrench (two sizes, or three?) and star. Don't remember what wrench sizes are needed for the primary mirror, (done once lasts forever) the sec. mirror is 4 mm Allen key (quite a different torque from what you might know from SC scopes)

How about DSO's? Planets perhaps would be okay even if the collimation slightly moved, but wouldn't it decrease the quality of DSO's images?

[Bill Barlow]

I'm also considering to buy an SCT 6", C6 xlt if a CC is not suitable for my goal. I want to image of course planets, and lunar-- and small DSO's like planetary nebulae, clusters and maybe a small galaxies and bright galaxies. I think CC provides well detailed view of objects due to its special optical design, and also a nice performance in imaging. So CC's kind of attractive to me. Compared to C6, what's good about CC6? I'd like to inform you guys that, my budget is quite limited. 

I have owned the CC6 and a C6, both had very good optics.  I thought the CC sky background was a bit darker than the SCT.  The main differences to me was the CC6 weighed about 4 pounds more than the C6 and was very back heavy with the Crayford focuser.  

[Staradventure21]

I have owned the CC6 and a C6, both had very good optics.  I thought the CC sky background was a bit darker than the SCT.  The main differences to me was the CC6 weighed about 4 pounds more than the C6 and was very back heavy with the Crayford focuser.  

Are there some significant optical performance differences CC6 and a C6?

[Magnus Ahrling]

I bought a GSO CC8 second hand last april so I have now had it for a year. Used it quite often. I am not an imaginer, only a visual observer! I have done a slight collimation on the secondary, the same way as I collimate my C8 . No troubles so far. But I have not touched the primary as I found no need for that. In good seeing, in my opinion, stars and planets are very razorsharp in this CC8 GSO Classic Cassegrain. I   like observing double stars/planets and when seeing permits I can go >400X on doubles. ~250X on Jupiter and ~300X on Mars when it was in opposition. I would say it`s very much like a bigger version vs my Intes MK66 Mak.

 

Indeed it`s a bit heavy, 9-10kg. Still works fine on my Vixen GP+Celestron tripod with 2" steellegs. I use a simple Sky-Watcher RA drive for tracking.

 

I bought the scope because I was intressted how I should like a Classic Cassegrain. So when I got the opportunity to get a used one for a good price I took the chance. And yeas I like it after 1 year of using it

 

So my conclusion is collimating a Classic Cassegrain can be easy but I don`t say it can`t be difficult..... The GSO manual has instructions how to collimate the CC8/CC6.

 

 Clear & Steady Skies to you all,

Magnus

 

PS collimation was done using real stars in the sky.

[Bill Barlow]

Are there some significant optical performance differences CC6 and a C6?

As I mentioned before, the sky background is a little darker in the CC6 and focused stars seemed more pinpoint.  A nicer view, but the excessive back weight made me return it.  If the weight doesn't bother you, I would go for the CC6.

 

Bill

[Staradventure21]

As I mentioned before, the sky background is a little darker in the CC6 and focused stars seemed more pinpoint.  A nicer view, but the excessive back weight made me return it.  If the weight doesn't bother you, I would go for the CC6.

 

Bill

Thx Bill!! Could buying a new focuser decrease the weight of the OTA?

[rmollise]

Hello there. I've been using my Nexstar 4se for three years, and now I'm seriously contemplating to buy a new OTA. I will have an AVX Eq mount really soon, and I'm going to put the OTA on it. So, here's the question: Is it hard to collimate GSO CC6 classical cassegrain? I've heard that it's quite tricky to collimate CC, is it true? If so, how much is difficult to collimate a CC?

"Difficult" is relative. Certainly, when you've got two adjustable elements, primary and secondary, it becomes more difficult than a system with one, like the SCT.

 

Back in the glorious days, Celestron's white-tube scopes had adjustable primaries in addition to secondaries, which caused no end to customer confusion.

 

Like most things, knowing what to do, and how to do it, and getting a little practice makes it easier. 

[Staradventure21]

"Difficult" is relative. Certainly, when you've got two adjustable elements, primary and secondary, it becomes more difficult than a system with one, like the SCT.

 

Back in the glorious days, Celestron's white-tube scopes had adjustable primaries in addition to secondaries, which caused no end to customer confusion.

 

Like most things, knowing what to do, and how to do it, and getting a little practice makes it easier. 

Thank you for such a good advice. I think I will have to face a lot of troubles while collimating a CC lol. But as you said, I believe it would much be easier when I knows what to do, and how to do it! Thank you agian, Rmollise.

[Staradventure21]

I bought a GSO CC8 second hand last april so I have now had it for a year. Used it quite often. I am not an imaginer, only a visual observer! I have done a slight collimation on the secondary, the same way as I collimate my C8 . No troubles so far. But I have not touched the primary as I found no need for that. In good seeing, in my opinion, stars and planets are very razorsharp in this CC8 GSO Classic Cassegrain. I   like observing double stars/planets and when seeing permits I can go >400X on doubles. ~250X on Jupiter and ~300X on Mars when it was in opposition. I would say it`s very much like a bigger version vs my Intes MK66 Mak.

 

Indeed it`s a bit heavy, 9-10kg. Still works fine on my Vixen GP+Celestron tripod with 2" steellegs. I use a simple Sky-Watcher RA drive for tracking.

 

I bought the scope because I was intressted how I should like a Classic Cassegrain. So when I got the opportunity to get a used one for a good price I took the chance. And yeas I like it after 1 year of using it

 

So my conclusion is collimating a Classic Cassegrain can be easy but I don`t say it can`t be difficult..... The GSO manual has instructions how to collimate the CC8/CC6.

 

 Clear & Steady Skies to you all,

Magnus

 

PS collimation was done using real stars in the sky.

Thank you for sharing your experience, Magnus! I'd like to ask you something. Have you tried to see some clusters like M13 or M5? How was the resolution of the OTA?

[GrassLakeRon]

when did you buy your CC?

I bought it from Agena in spring of 22.  Agena collimated it and its still perfect today.  I have a handmade case with 3" of foam to hold the scope in.