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LOOKING FOR ADVICE-8" RC Push On or Return It?

Beginner Equipment Reflector Collimation
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#1 Jax_Images

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Posted 25 October 2021 - 09:16 AM

I recently purchased an 8” IOptron RC Scope. My first images have been disappointing. I am attaching a two images that I took based on advice from my local Astronomy club. I am convinced that my collimation is off. I’ve read numerous threads and watched several videos on collimating RC scopes. Right  now I am leaning towards returning the scope and saving up for either a nice refractor or another type of reflector. I paid $1,000 for the scope and while I am willing to try and refine the collimation, I won’t spend $100-500 on accessories to fix something that is right out of the  box, literally. Opinions?

PS- My primary interest is in photographing DSO, Distant Galaxies and Nebula. I’ve been happy with using some telephoto lenses and a H-alpha modded DSLR. Was looking to move into the ~1500mm focal length.Small fomalhaut 100ms out of focus.jpg median stack m25 test file tight crop centyer of image.jpg



#2 John Miele

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Posted 25 October 2021 - 09:39 AM

Yep. You are severely out of collimation. 

 

I personally would never buy the 8" RC scope again for this reason ( I owned 2 of them). I spent more time trying to collimate than image. some people just seem to have no issue but I struggled. When collimation was on the money, the scope was a terrific performer. But when it goes out...


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#3 GaryShaw

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Posted 25 October 2021 - 09:43 AM

Hi

We don’t know from your post what mount or other key gear you are using or what your experience level is. If your club is coaching you on how to image, perhaps that’s an indication of your current experience being at the novice/ newbie level - nothing wrong with that but EAA observing or Imaging woes time to learn and requires the right equipment and a reasonable degree of experience to pull off the images we all see here in CN. All these factors are important in determining what results to expect with a new scope. It took me six months + to learn to use my first setup and to learn to operate my observing process with Sharpcap. Things in this pursuit take time and patience to master.
 

So, the above is my perspective after nearly 4 years of experience - perhaps you have that experience, we don’t know. One thing is clear however, any reflector scope that was shipped through the mails is bound to need collimation prior to use. I have no experience with RC scopes, but I know that Newtonians need collimation once in a while and definitely after being shipped, bumped, or just knocked about a bit during normal use. Assuming RCs are not that different from Newtonians, you should expect to have to purchase a few simple collimation tools ( a cheshire and laser collimator from Farpoint are adequate at 120 usd) and then learn to use them correctly. It’s a required part of the process with any reflector.

 

Before returning the scope, I suggest that you collimate it, be sure you’re clear on how to use it with your other gear, and do some more thorough testing to verify if there’s really a problem with the RC. Good luck.

Gary 
 


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#4 bobzeq25

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Posted 25 October 2021 - 09:57 AM

I spent several weeks collimating my 6RC.  It bears no resemblence at all to collimating a Newtonian.  The two mirrors interact.  You can't collimate one then the other, you have to go back and forth sneaking up on it.

 

You could try just collimating the secondary.  Maybe you'll get lucky, and the primary collimation will be good.  Mine wasn't.

 

Then I found out that the sloppy focuser messed with my careful collimation at various altitudes.

 

Many people solve that with a Moonlight focuser.  $$$.   At that point I already had about $1200 in the "$400" scope.

 

I personally bought a nice 3.7 inch rack and pinion focuser

 

It came attached to a TS 130mm F7.  <smile>


Edited by bobzeq25, 25 October 2021 - 10:00 AM.

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#5 John Miele

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Posted 25 October 2021 - 02:36 PM

 

 

I personally bought a nice 3.7 inch rack and pinion focuser

 

It came attached to a TS 130mm F7.  <smile>

I love this every time I see you post it...lol!


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#6 Rasfahan

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Posted 28 October 2021 - 06:43 AM

So, to be helpful before you send back the scope. Your collimation is severely off. You need to go back to basics. Here‘s a (my) workflow. It gets me to acceptable performance, I have not cracked perfect yet for APS-C sensor on a RC. I‘ve been practicing for a year, first with a 8“ GSO RC (like yours), now with a 10“ CFF RC (a truss design). 

 

A: The below seems too daunting? Yes => X, No => 1.

  1. Remember the number 1. Check with a good laser if your focuser is pointing to the center of the secondary. Yes => 4. No => 2.
  2. Can your focuser be tilt-adjusted? Yes => 3, No => X.
  3. Adjust the tilt of the focuser with help of your laser. Does it keep centered in all sky positions of the scope? Yes => 4, No => X
  4. Use a good Cheshire (or Takahashi collimating scope or the REEGO) to get secondary alignment good. Do a star test. Is on-axis good? Yes => 5. No => 6.
  5. Are off-axis aberrations balanced (= the star shapes are point symmetrical to the center)? Yes => F, No =>7
  6. Carefully, with very small adjustments, use the primary to make the on-axis performance somewhat better. Repeat until off-axis is balanced and on-axis is good or until off-axis becomes unbalanced. Off-axis unbalanced => 7, Both good => F
  7. Carefully, with small adjustments, use the secondary adjusters to make star shapes balanced with regard to the center. Get this close to perfect. Add one to your number. Is it 30? => X. Is on-axis good? Yes => F, No => 6.

F: You did it.

X: Return the telescope.

 

Although presented here a bit tongue-in-cheek, this is actually what I am doing. This method is tedious but it works without expensive equipment. It also leaves out the not-unimportant separation between primary and secondary mirrors (but that does not cause strange star shapes if off a bit). The REEGO (also known as TSRCColli) can bring you close. You might need to remove the central baffle tube extension to be able to use it correctly. The only other collimation aid I have found to work is the Hotech Advanced SCT laser collimator. It is $600, and not faster to lead to a result but can be used inside.

 

I need between 15 and 90 minutes to get an acceptable collimation. So, plan for a few hours. I’m a bit daft, I needed 20 on my first try. I’m sure you can do better. If this does not seem like a good pastime => X.

 

Good luck!waytogo.gif


Edited by Rasfahan, 28 October 2021 - 06:46 AM.

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#7 Jax_Images

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Posted 28 October 2021 - 09:18 AM

Thank you for the inputs. I have since purchased the following gear. 2” Cheshire eyepiece; 2” HG Collimator w/the concentric ring holograph; and the Self-Barlowed attachments.

 

Here is my Plan. First using the Cheshire look to see if the Secondary mirror is where it is supposed to be. Then do the same for the primary mirror. I found this on the web and it seems to capture some of the basics AND it looks doable.

https://www.astronom...-manual-pdf.pdf

 

If i can get those steps complete do a star test. Based on the star test. I may go to the steps outlined in the Video I found online which seems a bit complicated but I think I can manage with the help of a friend.

https://www.youtube....h?v=a3UOGDUaq6o

 

Next purchase is a decent set of T-handle Allen wrenches. If I can get through all these steps and still can’t get good images I may either get a focuser tilt adjustment plate or even a new focuser. At that point I might re-evaluate returning the scope. Thank you for all that chimed in. I’ll report back when I get results.
Respectfully
Jack


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#8 bobzeq25

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Posted 28 October 2021 - 09:34 AM

So, to be helpful before you send back the scope. Your collimation is severely off. You need to go back to basics. Here‘s a (my) workflow. It gets me to acceptable performance, I have not cracked perfect yet for APS-C sensor on a RC. I‘ve been practicing for a year, first with a 8“ GSO RC (like yours), now with a 10“ CFF RC (a truss design). 

 

A: The below seems too daunting? Yes => X, No => 1.

  1. Remember the number 1. Check with a good laser if your focuser is pointing to the center of the secondary. Yes => 4. No => 2.
  2. Can your focuser be tilt-adjusted? Yes => 3, No => X.
  3. Adjust the tilt of the focuser with help of your laser. Does it keep centered in all sky positions of the scope? Yes => 4, No => X
  4. Use a good Cheshire (or Takahashi collimating scope or the REEGO) to get secondary alignment good. Do a star test. Is on-axis good? Yes => 5. No => 6.
  5. Are off-axis aberrations balanced (= the star shapes are point symmetrical to the center)? Yes => F, No =>7
  6. Carefully, with very small adjustments, use the primary to make the on-axis performance somewhat better. Repeat until off-axis is balanced and on-axis is good or until off-axis becomes unbalanced. Off-axis unbalanced => 7, Both good => F
  7. Carefully, with small adjustments, use the secondary adjusters to make star shapes balanced with regard to the center. Get this close to perfect. Add one to your number. Is it 30? => X. Is on-axis good? Yes => F, No => 6.

F: You did it.

X: Return the telescope.

 

Although presented here a bit tongue-in-cheek, this is actually what I am doing. This method is tedious but it works without expensive equipment. It also leaves out the not-unimportant separation between primary and secondary mirrors (but that does not cause strange star shapes if off a bit). The REEGO (also known as TSRCColli) can bring you close. You might need to remove the central baffle tube extension to be able to use it correctly. The only other collimation aid I have found to work is the Hotech Advanced SCT laser collimator. It is $600, and not faster to lead to a result but can be used inside.

 

I need between 15 and 90 minutes to get an acceptable collimation. So, plan for a few hours. I’m a bit daft, I needed 20 on my first try. I’m sure you can do better. If this does not seem like a good pastime => X.

 

Good luck!waytogo.gif

Comments. 

 

You're not daft.  It takes many people _more_ than 20 hours.   I speak from (6RC) experience.  <smile>

 

The mirrors interact.   Some get lucky and get away with only adjusting the secondary.  People should definitely try that idea first.

 

Otherwise, instead of trying to get either mirror "perfect" on the early rounds, I suggest making small adjustments to each, and going back and forth.  I think that saves time, and lowers frustration.  It also may better tell you about if and when you've hit "X".  <smile>


Edited by bobzeq25, 28 October 2021 - 09:38 AM.


#9 Paul Sweeney

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Posted 31 October 2021 - 02:53 PM

I have a VC200L, which is an RC with a built in field flattener. Collimation can be a long and tedious task. But I have never seen an oval star test pattern.

Look into the tube from the front. You will see the secondary reflected in the primary. Putting your head in the same position left, right, above and below the view should look the same. If it looks significantly different, then the primary is off and not aiming at the center of the secondary.

Is your secondary tight. If it is not snug, it can move as the scope cools and the metal shrinks. This happened to me.

Is the secondary centered? Using the Cheshire, you should be able to look through it at the secondary. It should be centered and you should be able to see your eye in the middle. Many scopes use cast aluminum for the secondary spider, so there is no centering adjustment possible. Because the secondary is on a stalk, it will appear off center if it is out of collimation.

It could also be that the focuser is way off and not pointing at the secondary. Has the scope been dropped?

As you can see, all the components are linked. For the above, you are looking for rough alignment. Even a roughly collimated scope should show a round star test pattern but the central shadow will be well off center.

If mechanically everything is centered and nothing is bent or broken, try bringing the star through focus. Does your oval star test pattern change from vertical to horizontal as you pass through focus? If the scope is collimated and this happens, then you have astigmatism.

Does this happen visually, or only with the camera? With a diagonal? With different eyepieces?

I'm thinking that something is seriously out of alignment and light is being cut off. See if you can identify which, if any, component is out of alignment. Don't be afraid to mess with the collimation. It takes time and patience. Let us know what you find out.

Edited by Paul Sweeney, 31 October 2021 - 02:58 PM.


#10 osbourne one-nil

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Posted 31 October 2021 - 03:26 PM

Moved from Reflectors.



#11 Rasfahan

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Posted 31 October 2021 - 05:02 PM

I have a VC200L, which is an RC with a built in field flattener. Collimation can be a long and tedious task. But I have never seen an oval star test pattern.

Look into the tube from the front. You will see the secondary reflected in the primary. Putting your head in the same position left, right, above and below the view should look the same. If it looks significantly different, then the primary is off and not aiming at the center of the secondary.

Is your secondary tight. If it is not snug, it can move as the scope cools and the metal shrinks. This happened to me.

Is the secondary centered? Using the Cheshire, you should be able to look through it at the secondary. It should be centered and you should be able to see your eye in the middle. Many scopes use cast aluminum for the secondary spider, so there is no centering adjustment possible. Because the secondary is on a stalk, it will appear off center if it is out of collimation.

It could also be that the focuser is way off and not pointing at the secondary. Has the scope been dropped?

As you can see, all the components are linked. For the above, you are looking for rough alignment. Even a roughly collimated scope should show a round star test pattern but the central shadow will be well off center.

If mechanically everything is centered and nothing is bent or broken, try bringing the star through focus. Does your oval star test pattern change from vertical to horizontal as you pass through focus? If the scope is collimated and this happens, then you have astigmatism.

Does this happen visually, or only with the camera? With a diagonal? With different eyepieces?

I'm thinking that something is seriously out of alignment and light is being cut off. See if you can identify which, if any, component is out of alignment. Don't be afraid to mess with the collimation. It takes time and patience. Let us know what you find out.

 

The VC200L is very probably not a corrected RC (with two hyperbolic mirrors). Vixen calls it a "sixth order aspherical" - which, if I understood the theory of describing aspherical surfaces, really does not tell us anything useful. When the VC200L was released (2003), making precise hyperbolic surfaces was still extremely expensive and probably not possible to make to the price point of the VC200L. GSO still seem to be the only ones who can (or maybe want to) do it on the cheap with enough precision to get acceptable optics. The GSO RCs were released in 2008.

 

When collimation is off, the RCs will have these elliptical star shapes out-of-focus (mine do). To be as elliptical as the OP's image shows, it needs to be way out, of course (I haven't had mine as bad yet). The trick with collimating them under the stars is, basically, to get them nice and round on- and off-axis in the whole field.



#12 Jax_Images

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Posted 05 November 2021 - 03:39 PM

I received the Chesire EP. I was able to get a huge improvement using it and only adjusting the secondary mirror today, before and after images. Tonight I will try the star test. 

 

DSC1050 3new
DSC1055

 

 


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#13 jgraham

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Posted 05 November 2021 - 09:15 PM

+1

 

I hope that you can get the colimation under control. I love my RC8! I use it with my full frame EOS Ra and a Baader Mk III MPCC with wonderful results.



#14 Jax_Images

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Posted 05 November 2021 - 09:38 PM

I was able to get a pretty decent star test tonight. this is 10 shots mean stack in PS

Untitled 1 copy


#15 Rasfahan

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Posted 06 November 2021 - 01:33 AM

I was able to get a pretty decent star test tonight. this is 10 shots mean stack in PS

This is, of course, a lot better than the first one. It‘s still a bit off, though - how are the off-axis stars? I think it shows a bit of a triangular shape, too, which would hint at pinched optics. It‘s easy to pinch the secondary. Still, I‘ld call it 90% good. If your off-axis stars are balanced and your in-focus stars look decent in the corners, you‘re finished.


Edited by Rasfahan, 06 November 2021 - 01:35 AM.

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#16 GaryShaw

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Posted 06 November 2021 - 09:50 AM

This is, of course, a lot better than the first one. It‘s still a bit off, though - how are the off-axis stars? I think it shows a bit of a triangular shape, too, which would hint at pinched optics. It‘s easy to pinch the secondary. Still, I‘ld call it 90% good. If your off-axis stars are balanced and your in-focus stars look decent in the corners, you‘re finished.

Excellent advice!

We’d all be smart to remember the time-proven adage: “The perfect is the enemy of the Good.” 
 

Enjoy your RC

Gary



#17 PiotrM

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Posted 09 November 2021 - 07:10 AM

Takahashi collimating scope or the Teleskop Express similar collimator can handle RC/DK collimation quite easily.



#18 Rasfahan

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Posted 10 November 2021 - 03:47 AM

Takahashi collimating scope or the Teleskop Express similar collimator can handle RC/DK collimation quite easily.

As all other such collimation aids afterwards you need to fix collimation under the stars.


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#19 bobzeq25

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Posted 11 November 2021 - 04:00 PM

Takahashi collimating scope or the Teleskop Express similar collimator can handle RC/DK collimation quite easily.

There's a very large difference between collimating a DK with eliptical primary and spherical secondary, and a RC with two hyperbolic mirrors.  One of the many advantages of a DK.


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#20 Jax_Images

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Posted 12 November 2021 - 09:10 AM

here's my result from last night. glad I decided to push on. thanx to all who commented 

M33 For Web

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#21 Rasfahan

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Posted 12 November 2021 - 10:32 AM

Nice work - that must be quite a large sensor. Full frame?



#22 Jax_Images

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Posted 12 November 2021 - 12:51 PM

Yes it is, i displayed the entire frame so folks could look at the slight elongation of the stars in the corners. there is a little but the axis of the stretch seems to point to the center of the frame. from my reading this is about as good as i will be able to get. one thing that drew me to the RC design is how flat the field is w/o any correctors or other optics.


Edited by Jax_Images, 12 November 2021 - 12:56 PM.


#23 Rasfahan

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Posted 12 November 2021 - 12:58 PM

Yes it is, i displayed the entire frame so folks could look at the slight elongation of the stars in the corners. there is a little but the axis of the stretch seems to point to the center of the frame. from my reading this is about as good as i will be able to get. one thing that drew me to the RC design is how flat the field is w/o any correctors or other optics.

Yes, you won‘t get better stars full frame without a corrector. Well done.



#24 Jax_Images

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Posted 12 November 2021 - 01:02 PM

thanx again to you and everyone else that helped me out

Jack 


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#25 jgraham

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Posted 13 November 2021 - 04:09 AM

Fantastic! Quite by accident I found that the Baader Mk III MPCC does a nice job cleaning up the corners. My first night out I forgot that I had the MPCC installed on my camera. I took it off for my second night, put it back on for my third and it has been there ever since. :)

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