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8SE - Can't get point like stars

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#1 Curious Developer

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Posted 20 August 2019 - 06:49 PM

All, this is my first post. I am very new to this hobby and I hate for my first post to ask for help, but I am getting frustrated and I do not know anyone that can assist.

 

I bought a Celestron 8SE a few months ago. I was never able to get good focus for anything so I bought a Celestron Focus Motor. It helps but does not seem to be able to focus that much better than my manual focusing was doing. I also just bought a camera (ASI 294) so I could take some basic pictures. 

 

I have attached an example image that shows what stars look like from the camera. It supposed to be a picture of the Lagoon Nebula (I hope). Stars appear to be bright and point-like on the right hand side and really fuzzy on the left hand side. I thought it might be collimation, but when I defocus on a star the black spot appears to be centered.

 

image2.jpg

 

I am not sure if I have defective optics or if it really is a collimation problem, or if maybe there is some other problem and what I should do. I would really appreciate if anyone could look at my image and provide some guidance for me. Thank you in advance for any assistance you can provide.

 

Sincerely, Curious.



#2 spereira

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Posted 20 August 2019 - 06:55 PM

I'm going to move this over to Cats & Casses for better visibility for those who may be able to assist.

 

smp



#3 GoFish

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Posted 20 August 2019 - 06:56 PM

Are you able to bring objects into focus with a diagonal and eyepiece?

 

How is your camera connected to the back of the scope?



#4 Curious Developer

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Posted 20 August 2019 - 07:01 PM

Thank you for the quick reply.

 

Stars look just like this in my eye piece. I have also tried to remove the diagonal (which is the one that came with the telescope) but the stars still look like that pattern. 

 

The camera is inserted directly into to the diagonal. I can pull it out and put in an eye piece and it looks the same though.



#5 Eddgie

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Posted 20 August 2019 - 07:10 PM

The scope is badly out of collimation.

 

https://www.youtube....h?v=hqRVIDj4aZA

 

Look at the pattern at 37 seconds in the above video and note how similar that appears to the stars in your image (though in the video they are intentionally out of focus).


Edited by Eddgie, 20 August 2019 - 07:14 PM.


#6 Gary Z

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Posted 20 August 2019 - 07:22 PM

ok, Is this a new scope, or used?

 

What eyepiece are you using?

 

What eyepieces do you have?  What camera do you have and is zoom on?

 

Where do you live?  

 

Forgive the questions, but they do pertain to what you are seeing.  

 

When you took this image, how long had the telescope been with you outside?

 

 

When you are trying to check for collimation, you need to wait for about an hour for a C8.  This allows the telescope to get thermally adjusted.

 

Second, you want a 10 or 12mm eyepiece while viewing a 1st magnitude star, be sure whenever viewing thru the telescope for a star test that you center the star in your eyepiece.  

 

Now, if you can, reach out to a local or as local an astronomy club nearest you for assistance.  Having someone that can help collimate will serve to keep you calm while learning.  A friend of mine taught me and it helped me considerably.  That's why I asked where you live as we can help you locate the nearest club to your location.

 

If that isn't possible, we'll guide you further.

 

Gary



#7 GoFish

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Posted 20 August 2019 - 08:18 PM

Thank you for the quick reply.

 

Stars look just like this in my eye piece. I have also tried to remove the diagonal (which is the one that came with the telescope) but the stars still look like that pattern. 

 

The camera is inserted directly into to the diagonal. I can pull it out and put in an eye piece and it looks the same though.

While I agree it could be collimation, I’m betting you just haven’t turned the focuser enough times to reach focus. Seems like that knob will turn about 100 times before getting to the stops!

 

Have you run the focuser all the way to the stops in both directions?

 

I just haven’t ever seen a SCT that far out of collimation. 



#8 Boom

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Posted 20 August 2019 - 08:23 PM

Maybe you defocused too far out when you were checking collimation. If you defocus excessively, you will always get a centered donut.

#9 stryker66

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Posted 20 August 2019 - 08:40 PM

This is probably not collimation issue, its more of a misfocus issue. The high contrast white dot in the middle indicates misfocus. Maybe you need to check on your camera's backfocus distance.. 



#10 Bill Barlow

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Posted 20 August 2019 - 09:14 PM

If I were looking through a scope and saw this, I would say it's collimation is way off like some others have said.  The collimation error seems to extend between the 2 o'clock and 7 o'clock positions.  Try and adjust the secondary mirror screws if they are in these positions.  Don't give up hope as it should be an easy fix, just take your time.

 

Bill



#11 astro_1

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Posted 20 August 2019 - 09:36 PM

Maybe work with it during the day looking at a distant light pole or something. See how well the focus is with what ever eyepieces you have. If it focuses to a sharp image then move on to the camera and see if you can attain a sharp focus thus finding your back focus.

 

Then try the star test at night.



#12 Jetfuel

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Posted 20 August 2019 - 09:52 PM

Yes the collimation is out.  Check that the screws for the red dot finder etc. are blocking the mirror movement.  Look inside the scope and see if it clears them.  Then you will have collimate.



#13 Asbytec

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Posted 21 August 2019 - 09:22 AM

Looks like miscollimation to me.



#14 John Miele

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Posted 21 August 2019 - 02:20 PM

Classic miscollimation.

#15 Curious Developer

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Posted 21 August 2019 - 08:30 PM

Thank you all for the insights and helpful advice. Let me provide the requested information:

 

  • Is the scope new or old? - It is new as of 3 months ago. I purchased it from a local camera store. It was all sealed, and I think it had been shipped to his store about 3 months prior.
  • Has the focuser been configured? Yes. I used the focus motor and accompanying software to perform a setup on the focuser that initialized its minimum and maximum bounding positions.
  • What eyepiece are you using? I have experienced this exact artifacting with the Plossl 32mm, 25mm, 17mm, and the other ones are just too blurry to be used at all (12,8,6).
  • What camera do you have and is zoom on? There is no zoom, it is the ZWO ASI294MC Pro.
  • Where do you live? Near Toronto, Canada (London, Ontario to be specific)
  • When you took this image, how long had the telescope been with you outside? About 3hrs.

 

Some other (hopefully useful) details:

 

  • I have used it a fair amount. In the last three months my wife has complained a lot...almost every night that I can see a star or two I am out there for hours.
  • I used the focuser for about 2 months before purchasing the focus motor. I purchased the motor because I thought perhaps it required finer tuning to focus correctly.
  • It has looked like this since the beginning, so it has not degraded over the time I have used it.
  • After each use I replace the lens cap. I never leave any of the lens equipment exposed directly for any length of time. I also always keep the lens covers facing down so they won't collect dust.
  • I also have the Celestron 1.25" eyepiece/filter kit.
  • I have used the red-dot finder to setup the scope to an object about 400 meters away. It was fuzzy and I could not get a sharp focus. I have used this object several times.

I have attached an image from the camera. This is the image I get through the scope to an artificial star that is about 40 feet away. The focuser is at minimum. This looks exactly how I see it with the PLOSSL 32mm eyepiece as well.

Attached Thumbnails

  • Capture_00002-1.png

Edited by Curious Developer, 21 August 2019 - 08:56 PM.


#16 Gary Z

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Posted 21 August 2019 - 08:57 PM

Thank you all for the insights and helpful advice. Let me provide the requested information:

 

  • Is the scope new or old? - It is new as of 3 months ago. I purchased it from a local camera store. It was all sealed, and I think it had been shipped to his store about 3 months prior.
  • Has the focuser been configured? Yes. I used the focus motor and accompanying software to perform a setup on the focuser that initialized its minimum and maximum bounding positions.
  • What eyepiece are you using? I have experienced this exact artifacting with the Plossl 32mm, 25mm, 17mm, and the other ones are just too blurry to be used at all (12,8,6).
  • What camera do you have and is zoom on? There is no zoom, it is the ZWO ASI294MC Pro.
  • Where do you live? Near Toronto, Canada (London, Ontario to be specific)
  • When you took this image, how long had the telescope been with you outside? About 3hrs.

 

Some other (hopefully useful) details:

 

  • I have used it a fair amount. In the last three months my wife has complained a lot...almost every night that I can see a star or two I am out there for hours.
  • I used the focuser for about 2 months before purchasing the focus motor. I purchased the motor because I thought perhaps it required finer tuning to focus correctly.
  • It has looked like this since the beginning, so it has not degraded over the time I have used it.
  • After each use I replace the lens cap. I never leave any of the lens equipment exposed directly for any length of time. I also always keep the lens covers facing down so they won't collect dust.
  • I also have the Celestron 1.25" eyepiece/filter kit.

I have attached an image from the camera. This is the image I get through the scope to an artificial star that is about 40 feet away. The focuser is at minimum. This looks exactly how I see it with the PLOSSL 32mm eyepiece as well.

Great responses to our questions and comments!!!! So, that 12mm eyepiece is the one you want to use to collimate.  I believe everyone sees that your scope needs collimation.  If you use that artificial star to get you going with that 12mm and you review that video from Astronomy and Nature TV about collimation, you should get so much closer to collimate.  I've used an artificial star to collimate, but nothing beats a true star to collimate on.

 

Remember as the video instructs repeatedly, always center in the eyepiece when checking collimation or making adjustments.  And, You should be able to determine which screw to start with.  Some folks recommend trying to tighten, but you won't need to put much force in it.  This is why I prefer Bobs knobs over screws.  I'd rather place my fingers near the glass than the tip of screw driver, but to each is own.  

 

Here is a link of instructions by Mr. Rod Mollise that in addition to the video link provided to you early in this thread, may help:

 

https://skywatch.bra...collimation.pdf

 

Gary



#17 Boom

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Posted 21 August 2019 - 09:02 PM

That's way too much defocus to do any meaningful collimation.

 

The PDF linked by Gary is a good guide.


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#18 Curious Developer

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Posted 21 August 2019 - 09:17 PM

Great PDF. Thank you.


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#19 GoFish

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Posted 21 August 2019 - 10:31 PM

I believe that working on collimation before you fix the focus problem is a waste of time and will potentially make things worse. 

 

There is is something wrong with either your focuser, or the way you are using it. 

 

I’m assuming you have done this, but I’m going to suggest it anyway because it is methodical and will set a baseline of information for the cast of characters trying to help lol.gif :

  • Point the scope at a star, real or artificial
  • Put the visual back (only) on the scope
  • Insert a 90 degree, 1.25” diagonal into the visual back
  • Insert of medium focal length EP, say 25mm, into the diagonal
  • Turn the focuser clockwise as far as it will go 
  • While looking through the eyepiece at the star, turn the focuser counter-clockwise
  • Is there a point of best focus* reached before hitting the focuser stop?  What does the star look like at that point of best focus, if any?
  • How many full rotations of the focus knob are required to go from one stop to the other?

Until we know if your focuser is operating like it should, I’m outta here. 

 

* best focus = the point where turning the knob either way makes the focus worse 


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#20 Astrojedi

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Posted 22 August 2019 - 08:13 AM

The first image looks like miscollimation / misalignment of the secondary and/or the corrector. But I have a couple of questions.

The first image you posted... was it a crop from the center of the frame or one of the corners? What about the donut? Was that star centered in the fov?

Even with miscollimation / misalignment it is possible to get a somewhat centered donut somewhere in the field. But if it is off center it is likely because the secondary is misaligned and as a result the seagull stars will be more pronounced in the other corner / edge.

Another thing to keep in mind is that a regular SCT cannot produce pinpoint stars to the edges with a 4/3 sensor without a corrector due to spherical aberrations. That is just asking for too much. Even with the 6.3 corrector you are unlikely to get sharp stars across the fov with a 4/3 sensor.

If you want to image with a 4/3 or larger sensor you need to get the EdgeHD version.


Edited by Astrojedi, 22 August 2019 - 08:15 AM.


#21 starbuckin

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Posted 22 August 2019 - 12:23 PM

Just to reiterate Boom's point that if you're way out of focus, you will always get a nice looking donut.

 

Try to bring the focus to a point slowly. The donut should stay perfectly centered (not in the scope, I mean should look like a nice donut) all the way to a point. (you may have to keep re-centering in the scope while you do this).

In other words, you should see a perfect donut all way in until it becomes a point.


Edited by starbuckin, 22 August 2019 - 01:49 PM.

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#22 Curious Developer

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Posted 22 August 2019 - 05:32 PM

Thank you both for providing more things to think about.

 

To respond to the questions:

 

Was the first image a crop from the center of the frame or one of the corners? It was sort of from the center-ish. I have attached a full reference image with the highlighted area that was cropped to.

whole.jpg

 

What about the donut? Mostly centered. I have attached the full reference image (resized and compressed)

whole2.png

 

Was that star centered in the fov? yes, as best I could get it.

 

Please note that I cannot focus this to a point. This is at about the minimum the focuser allows me to go. 


Edited by Curious Developer, 22 August 2019 - 05:34 PM.


#23 elwaine

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Posted 22 August 2019 - 05:43 PM

If you can't focus the donut to a point, it's time to take it back to your dealer or contact Celestron and send it to them. It's under 2 years old, so it's still under the Celestron warranty. 


Edited by elwaine, 22 August 2019 - 05:46 PM.


#24 Boom

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Posted 22 August 2019 - 05:50 PM

Minimum close focusing distance of the 8SE is 25 feet I believe?  That's with a normal diagonal and eyepiece.    If you are sure the artificial star is at 40 feet, and you're using nothing but the stock diagonal and eyepiece, then something might be wrong with the scope if you can't reach focus.



#25 whizbang

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Posted 23 August 2019 - 09:15 AM

For proper collimation:

 

1) High power eyepiece, 6 to 9mm for your scope, and

 

2) Very near, or just off focus.

 

A 32mm eyepiece is wide field and will never help you collimate.  Your attached image is de-focused far too far.  When one de-focuses too much, a badly collimated scope will still produce a donut.  High power, near focus, is where the collimation errors show up.


Edited by whizbang, 23 August 2019 - 09:15 AM.



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