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Orion 8" Classical Cass giving soft view - collimation?

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#26 rexowner

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Posted 24 July 2021 - 03:03 PM

For visual use, what EP’s are you using? I am using in 56mm to 7mm without having to swap extensions. The EPs are a mix of 50’, 82’, and 44’ othros. The focus is sharp on the moon, open clusters, globular clusters, and few diffuse objects, Galaxies are a challenge from bortle 8 and an 8” scope.

Those I´ve had in the diagonal:

- 10, 20, 30, 40MM Pentax XW

- 55mm Tele Vue Plossl

- 25mm ES 100

- 21mm Ethos

- Several Delos

 

Honestly, I need to spend more time with the scope, and maybe it needs some tuning, but

with everything I've done so far, the view from my 5" refractor shows more detail, and is

not noticeably dimmer.  I'm trying to like this scope and find a reason to keep it.



#27 David Boulanger

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Posted 24 July 2021 - 03:59 PM

Mine came two days ago.  Collimation seems O.K. even after the UPS guy did not treat it like the fragile words on the box would expect.  Imaged Jupiter.  Imaging with out a diagonal required all three spacers before the focuser and then another 35mm of spacers before my ASI 183.  That puts the focuser in about the middle of its travel.       



#28 pweiler

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Posted 24 July 2021 - 09:10 PM

Those I´ve had in the diagonal:
- 10, 20, 30, 40MM Pentax XW
- 55mm Tele Vue Plossl
- 25mm ES 100
- 21mm Ethos
- Several Delos

Honestly, I need to spend more time with the scope, and maybe it needs some tuning, but
with everything I've done so far, the view from my 5" refractor shows more detail, and is
not noticeably dimmer. I'm trying to like this scope and find a reason to keep it.

I hope you get it tuned to your liking and keep it. I am interested how the views through the 100’ EP’s look once collimated. I “only” have 82’ max and I am surprised how flat through the entire eyepiece the view is in the 82’s. Wondering if that is true with even wider field eyepieces in the cc8. If you already have a high quality 5” refractor, it is probably going to be hard to beat. Where I am at, the cc8 is nice to not have to deal with dew management. Back on the topic of collimation, you and others may be interested that after 14 hours of driving (7 hours each way with bumps and not in a luxury vehicle). I thought the collimation on the cc8 would be a wreck - didn’t have to tweak it at all.

Edited by pweiler, 24 July 2021 - 09:12 PM.


#29 rexowner

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Posted 25 July 2021 - 12:12 AM

I would be concerned about "oval". If it is noticeably oval, and the major axis rotates 90 degrees when you go to the other side of focus, that is astigmatism (which can be in your eyes or your eyepiece, too, of course).

Good point.  Oval is *very* slight.  I don´t normally rotate my head at the eyepiece, but when I did,

the oval seemed to follow, so likely my right eye.  Last checkup was about a year ago, and about

0.5 diopter of astigmatism.



#30 titanio

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Posted 25 July 2021 - 02:23 AM

One thing very important to avoid soft views,  together with a good collimation and cool down, it is very important also the quality of the diagonal and eyepieces and to use the correct power do not put too much power and do not observe the planet when it is over the roofs.

 

Cheers 



#31 quilty

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Posted 25 July 2021 - 04:31 AM

Those I´ve had in the diagonal:

- 10, 20, 30, 40MM Pentax XW

- 55mm Tele Vue Plossl

- 25mm ES 100

- 21mm Ethos

- Several Delos

 

Honestly, I need to spend more time with the scope, and maybe it needs some tuning, but

with everything I've done so far, the view from my 5" refractor shows more detail, and is

not noticeably dimmer.  I'm trying to like this scope and find a reason to keep it.

You're at the same point as me. I own a 6 inch CC but the issues are the same. Like how it looks, the built-in dewshield and the easy assembly, everything is plain to see. And the design in general, but:

Are you aware that your scope is just a 7.34 inch one? Mine is a 5.4. And my true 5 inch Maksutov provides more detail and contrast.

I collimated the scope with almost maximum mirror distance and since then I only need 1 inch extension with the 2 inch diagonal no matter what eyepiece. (any mm more mirror distance yields about 15 mm less focal length). And still: see if the primary mirror is fixed otherwise sharp views  just come by incidence.

Maybe a better alternative would be the 180 mm Skywatcher Maksutov, when you're used to refractors and after razorsharp views on planets, moon and small objects.

 

Question to all 8 inch CC observers: even if the 6 mm 1.25 66° golden edge eyepieces might be sub-level to you but when you watch through it the termnator, do you also see that annoying very bright golden ring in the middle of FOV? I do and this seems to be another disease of these scopes.


Edited by quilty, 25 July 2021 - 06:07 AM.


#32 petert913

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Posted 26 July 2021 - 03:49 PM

My CC8 gave great views last night during First Light.  Details on Jupiter and Saturn were much sharper than with my Celestron C8.  I notice when focusing on a far away tree, it took ALL 4 of my extensions to come to focus.  But when focusing on stars, the single 2" extension was fine for all my EP's.   Still running it through "do you love me yet?" testing :)


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#33 pweiler

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Posted 26 July 2021 - 05:03 PM

You're at the same point as me. I own a 6 inch CC but the issues are the same. Like how it looks, the built-in dewshield and the easy assembly, everything is plain to see. And the design in general, but:
Are you aware that your scope is just a 7.34 inch one? Mine is a 5.4. And my true 5 inch Maksutov provides more detail and contrast.
I collimated the scope with almost maximum mirror distance and since then I only need 1 inch extension with the 2 inch diagonal no matter what eyepiece. (any mm more mirror distance yields about 15 mm less focal length). And still: see if the primary mirror is fixed otherwise sharp views just come by incidence.
Maybe a better alternative would be the 180 mm Skywatcher Maksutov, when you're used to refractors and after razorsharp views on planets, moon and small objects.

Question to all 8 inch CC observers: even if the 6 mm 1.25 66° golden edge eyepieces might be sub-level to you but when you watch through it the termnator, do you also see that annoying very bright golden ring in the middle of FOV? I do and this seems to be another disease of these scopes.


No weird rings viewed, but I have only gone up to 343x with a 7mm and that only provides a better view under really clear and steady skies. Your 6mm would deliver 400x in the CC8 - that is a lot of power I think for a CC8. One of the nice aspects of f/12 in a CC8 is that you don’t have to use a pin hole eyepiece to get a comfortable, wide field of view at well over 100x.

#34 rexowner

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Posted 26 July 2021 - 10:27 PM

...I notice when focusing on a far away tree, it took ALL 4 of my extensions to come to focus.  But when focusing on stars, the single 2" extension was fine for all my EP's. ...

I have used, 0, 1, 2 or all three extensions to come to focus in different situations. 

 

I'm all in for a science project, but would like to understand what it is about the optics of this CC

design that seem to require a focuser without extensions to need on the low end 4", and the high

end 6", of travel to accommodate different setups.

 

I guess this is OK if you like fussing with your equipment and threading extensions on and off.

Doesn't seem ideal for concentrating on observing.



#35 pweiler

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Posted 26 July 2021 - 11:11 PM

I have used, 0, 1, 2 or all three extensions to come to focus in different situations.

I'm all in for a science project, but would like to understand what it is about the optics of this CC
design that seem to require a focuser without extensions to need on the low end 4", and the high
end 6", of travel to accommodate different setups.

I guess this is OK if you like fussing with your equipment and threading extensions on and off.
Doesn't seem ideal for concentrating on observing.


Daytime will need extensions, achieving focus at nearby objects will be a much different setup.
Astrophotography will most likely need a different setup.
Night Visual Use from around 50x to 300x should be able to use the same extension length, extreme low and high power might need an adjustment depending on the EP and diagonal used. Eye sight issues can also be a factor.

#36 quilty

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Posted 27 July 2021 - 06:31 AM

I have used, 0, 1, 2 or all three extensions to come to focus in different situations. 

 

I'm all in for a science project, but would like to understand what it is about the optics of this CC

design that seem to require a focuser without extensions to need on the low end 4", and the high

end 6", of travel to accommodate different setups.

 

I guess this is OK if you like fussing with your equipment and threading extensions on and off.

Doesn't seem ideal for concentrating on observing.

I'm quite sure that any scope of that focal length, unless it focusses by the primary mirror, will require long backfocus adaptions every once in a while. In order to give you more stuff to fuss:

I've just got rid of my last 1 inch extension by increasing the mirror distance by some mm, see pic (c by Russkiy). You can losen the baffle and screw the fixing ring and baffle in to the end. The result in my case is 30 mm less backfocus. This is powerful to adjust the need of backfocus. Don't know how this affects aspheric correction, my guess is nothing visible.

I wonder if the GSO design is so appropriate that they have forseen the fact that this mirror distance shift possible seems to match the 4-5 inch focus shift on the backside possible by the extension rings

Attached Thumbnails

  • mirror distance.jpg

Edited by quilty, 27 July 2021 - 08:33 AM.


#37 jgraham

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Posted 27 July 2021 - 09:32 AM

SCTs have a huge focal range since they move the focal plane by moving the primary. With CCs the position of the focal plane is fixed, so you need to moved the focuser. One spacing should work for visual, but you need different options to accommodate different cameras.

I really like the fixed optics of the CC design. You can do something similar with an SCT by adding an external focuser and fixing the primary in a sweet spot.
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#38 rexowner

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Posted 27 July 2021 - 09:50 AM

I also like the fixed optics position of the CC design.  Make more sense to me to be able to see where the

focuser is moving -- if nothing else, it makes it easier to compare different eyepieces e.g. if one wants

to make them parfocal.  Not sure why this isn´t standard for SCTs or Maks since as you point out

you can basically retrofit a movable focuser to an SCT - I guess a strong focuser with 

4 or 6 inches of movement is more expensive than the parts to move the mirror inside the tube,

so it´s basically a cost-saving thing, even for high end SCTs?


Edited by rexowner, 27 July 2021 - 09:51 AM.


#39 quilty

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Posted 27 July 2021 - 10:13 AM

my guess is like this:

1. The Celstron SCT-design dates from the late seventies where stargazing was visual in the first place.

2. less weight. In the beginning hobby scopes used to be smaller, the mounts as well.

3. aspherical correction: CC and RC mirrors are more delicate concerning the optimum distance compared to spherical mirrors



#40 jgraham

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Posted 27 July 2021 - 10:56 AM

Here’s an interesting data point… I happen to own an early production Meade LX 2080, Meade’s first SCT introduced in 1980. It’s an excellent, well built scope with a few quirks found only on this early version. One characteristic is that the focal range is shorter than the contemporary C8s and later Meade SCTs, it works fine for all of the contemporary 1.25” eyepieces and diagonals as well as standard 35mm camera bodies (and modern DSLRs), but the focus range is too narrow for most 2” visual backs, diagonals, and eyepieces. This is the only SCT that I have used where I ran out of focus when trying to use my 2” eyepieces. Sooooo, there’s good reason to design flexibility into a system and a challenge for telescopes with fixed optics is accommodating a broad range of eyepieces and cameras. Accommodating cameras can be particularly challenging due to the back-focus requirements.

 

Food for thought.

 

P.S.

 

P.S.

 

Back in my ATM days I used to build Newtonians with a moveable mirror cell; one location for visual, the other for imaging. The difference between the two was about 1.5”, the depth of a 35mm camera body. :)



#41 quilty

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Posted 27 July 2021 - 11:11 AM

yes and that's another reason for the mirror focussing design: Maximum variablity. My 2080 dates from maybe 83 and is up to from 20 m distance till infinity without any spacer. You can use your artificial star for collimation in the backyard or identify insects on your flowers, count their legs, a true garden microsope without leaving your seat



#42 BobW55

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Posted 05 September 2021 - 12:53 PM

Having a hard look at this for planetary imaging on my CEM40 mount,

 

So those of you that have the CC8, have you used it for planetary imaging?

How do you like it for imaging, or would you get some thing else for planets?  



#43 David Boulanger

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Posted 05 September 2021 - 03:34 PM

I bought my C.C. for planets and lunar.  I'm happy.  Maybe a C8 would be more versatile with a focal reducer and Fastar option though.  



#44 Phil Barker

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Posted 05 September 2021 - 06:52 PM

these are good scopes collimation is a bit tricky IF both primary and secondary need tweaking.

 

I've done this with a cc200 and have plenty of experience doing cassergains including a big f17 14 inch.

 

Happy to provide  you with quick instructions simply ask :)

Makes a huge difference they are good optics for the money.



#45 BobW55

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Posted 05 September 2021 - 07:13 PM

these are good scopes collimation is a bit tricky IF both primary and secondary need tweaking.

 

I've done this with a cc200 and have plenty of experience doing cassergains including a big f17 14 inch.

 

Happy to provide  you with quick instructions simply ask smile.gif

Makes a huge difference they are good optics for the money.

May end up taking you up on that offer if I get one.




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