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PHD2 Calibration with Celestron 11’’ Edge HD Issue

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#1 Mikhail_K

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Posted 22 April 2019 - 09:30 PM

Hello,
I hope this is the right forum and someone can help me solve an issue I have been struggling with for at least three months. I am trying to venture into astro photography, and cannot get past PHD2 Calibration step. The equipment I use is:

        Celestron CGX mount
        Celestron 11’’ Edge HD
        Celestron 0.7 Focal Reducer
        Orion TOAG or Celestron OAG
        ZWO ASI 290 MM Mini guiding camera
        Canon 6D Mark II for now (but this is not relevant for this issue)

 

Initially I thought that I have a problem with my mount and it cannot track correctly. A friend came over and we used his equipment on my mount (a refractor with a guiding scope). Here is a screenshot of PHD2 calibration with his equipment:

 

https://photos.googl...U0wRVJScFB2dlhR

 

Then we tried to exchange different pieces of my setup trying to isolate a problem area. We have changed cables, laptops, guiding camera, switched from Orion TOAG to his Celestron OAG (which he used previously successfully on his SCT). No matter what we did, we would always get the same results. Tried default PHD2 setting, recommended settings found in various online posts, called High Point Scientific for a technical advice – same results. Here are some screenshots of “questionable” calibration results:

 

https://photos.googl...U0wRVJScFB2dlhR

 

https://photos.googl...U0wRVJScFB2dlhR

 

https://photos.googl...U0wRVJScFB2dlhR

 

https://photos.googl...U0wRVJScFB2dlhR

 

The scope was aligned using two alignment stars, four calibration stars, and then polar aligned. Once we got a perfect calibration with my friend’s equipment, we changed it to mine keeping the same polar alignment.

 

Has anyone ever seen this issue with PHD2 and similar equipment? PHD2 has recognized my guiding camera and has a correct pixel size. I entered 1960 as my focal length to account for 0.7 reducer.

Thank you for your help,
Mikhail.



#2 jdupton

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Posted 22 April 2019 - 09:43 PM

Mikhail,

 

   In the first two screen shots with your equipment, the focus of the guide star is way off. You can see that in both the enlarged guide star view and the star profile. Nothing will make much sense when the focus is that far out. In the first screen shot using your friend's equipment, notice the nice tight star pattern and steep pointy profile. 

 

   It also appears that your calibration step size needs to be tweaked. Even after you got better (but not great focus) in the last two screen shots with your equipment, the calibration steps do not seem to be far enough apart. Double check your camera pixel size input and then use the wizard to suggest a better calibration duration for each step. (Your focal length sounds close for the 11" with focal reducer. That's the same setup I use.)

 

 

John

 

EDIT: By the way -- Welcome to Cloudy Nights! -- I just noticed this was your first post here...


Edited by jdupton, 22 April 2019 - 09:58 PM.


#3 Dereksc

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Posted 22 April 2019 - 09:44 PM

One thing that stands out if you compare your friends PHD2 calibration to all of yours is that he has a much higher SNR on his guide star and it is not saturated. A saturated star will give poor results. Also focus should be better on your guide star.



#4 TelescopeGreg

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Posted 22 April 2019 - 09:51 PM


The scope was aligned using two alignment stars, four calibration stars, and then polar aligned. Once we got a perfect calibration with my friend’s equipment, we changed it to mine keeping the same polar alignment.

You need to do the polar alignment first, then align the telescope controller to the sky.  If you move the mechanical position of the mount, it's going to invalidate where the controller thinks the telescope is pointing. 



#5 jerahian

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Posted 22 April 2019 - 10:41 PM

I wouldn't worry about calibration until you figure out why your guide star looks like a smeared cloud.  No calibration will be a good calibration until that is resolved.

 

So, the things to think about are:

  1. Is it in focus?  Do you have the correct back focus spacing to your guide camera sensor?  From the google photos of your imaging train setup, it looks like you have a helical focuser for your guide camera, so be sure that you adjust that and see if your star profile changes to look more like your friend's setup.
  2. Is your OAG prism clean?
  3. Is it peaking out far enough into the light path (but not blocking your main camera sensor along its longer edge) to get good light?
  4. What does a single 3s shot from your 6D show?

Resolve this issue and I bet your calibration process will go smoother.

 

-Ara



#6 rgsalinger

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Posted 23 April 2019 - 12:11 AM

The guide star that you showed is useless.

 

I believe that you have the prism too far out. First, center the prism just above and parallel to the main camera chip. Then lower the prism until it casts a shadow on the main camera and then back it off just a bit.

 

Using a full frame camera means that you will inevitably have to have the prism pretty far off center. SCT's are not corrected that well and that guide camera has really small pixels. Make sure to bin the camera 2x2 which will help some.

 

Rgrds-Ross



#7 Mikhail_K

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Posted 23 April 2019 - 10:32 PM

Thank you very much for your suggestions. I'll try them all next time the weather permits (hopefully soon).

Appreciate your help!

-Mikhail.




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