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AI based wave front sensing and collimation

Collimation
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#426 Corsica

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Posted 29 April 2024 - 10:53 AM

In a few weeks, we'll release a new SKW update that will add some exciting features.

 

-1-    Balanced astigmatism score using a star field.
SKW computes automatically the level of balance even if the stars in the field are not at a constant distance from the chip center, as long as there are enough stars spread well over the field.

 

-2-    Sensor/image tilt score using a star field.
This SKW score is based on the scope's CFZ.

 

This update will be available free of charge for current and future SKW Collimator and Pro users.


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#427 Rasfahan

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Posted 29 April 2024 - 11:05 AM

What an awesome update! I had hoped for something like this to become available.

#428 arbit

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Posted 29 April 2024 - 11:59 AM

In a few weeks, we'll release a new SKW update that will add some exciting features.

-1- Balanced astigmatism score using a star field.
SKW computes automatically the level of balance even if the stars in the field are not at a constant distance from the chip center, as long as there are enough stars spread well over the field.

-2- Sensor/image tilt score using a star field.
This SKW score is based on the scope's CFZ.

This update will be available free of charge for current and future SKW Collimator and Pro users.

Great features. Looking forward to them.

Sent from my SM-S908E using Tapatalk

#429 RonaldNC

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Posted 29 April 2024 - 03:41 PM

Gaston,

 

This is great!

 

So, currently I get a 9.8 score on collimating my Hyperstar on my Celestron HD Edge 8"... but I still get crescent stars on the top part of the sensor/image.  Can I use this new feature to adjust the tilt on my ASI2600MC Pro?

 

Thanks,

Ron



#430 taraobservatory

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Posted 04 May 2024 - 02:30 AM

Hi Paul, 

 

 

Thank you :) 



#431 Object_FS

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Posted 10 May 2024 - 01:46 PM

In a few weeks, we'll release a new SKW update that will add some exciting features.

 

-1-    Balanced astigmatism score using a star field.
SKW computes automatically the level of balance even if the stars in the field are not at a constant distance from the chip center, as long as there are enough stars spread well over the field.

 

-2-    Sensor/image tilt score using a star field.
This SKW score is based on the scope's CFZ.

 

This update will be available free of charge for current and future SKW Collimator and Pro users.

Very interesting features Gaston laugh.gif

 

Will you update the SkyWave documentation as well, and add the detailed information about these new features?


Edited by Object_FS, 10 May 2024 - 01:46 PM.


#432 KTAZ

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Posted 19 May 2024 - 10:06 PM

This weekend I used SkyWave to collimate my 9.25" Edge. I ended up having to do trial and error at first in order to get a defocused star of the size and quality needed, but I was able to get everything dialed in eventually.

 

Very happy with the software. Many would say it is a bit pricey; however, I found it to be the best that I've used from the perspective of providing very clear analysis and tracking of your progress. I think I burned about a dozen credits; but 2/3 of those were burned after I foolishly decided an 8.9 score wasn't good enough. I ping-ponged back and forth for over an hour until I got, you guessed it, an 8.9.

 

I did gain a fresh appreciation for just how sensitive those collimation screws are. Seriously, the last adjustment that took me literally from an orange zone to the green was literally 1/32 turn. I barely knew that I turned it; I could only be sure by the slight movement on my loop.



#433 RonaldNC

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Posted 20 May 2024 - 01:57 AM

This weekend I used SkyWave to collimate my 9.25" Edge. I ended up having to do trial and error at first in order to get a defocused star of the size and quality needed, but I was able to get everything dialed in eventually.

 

Very happy with the software. Many would say it is a bit pricey; however, I found it to be the best that I've used from the perspective of providing very clear analysis and tracking of your progress. I think I burned about a dozen credits; but 2/3 of those were burned after I foolishly decided an 8.9 score wasn't good enough. I ping-ponged back and forth for over an hour until I got, you guessed it, an 8.9.

 

I did gain a fresh appreciation for just how sensitive those collimation screws are. Seriously, the last adjustment that took me literally from an orange zone to the green was literally 1/32 turn. I barely knew that I turned it; I could only be sure by the slight movement on my loop.

I agree with your experience.  It took a few trials and errors to get the image just right... orientation, exposure, focus setting, etc., but now it's pretty easy.  I was surprised at how a very small change makes such a big difference... particularly with my HyperStar.  That thing is very, very sensitive.

 

Now I'm wrestling with another problem with the HyperStar.  The center stars are very good, but the out-lying stars... not so much.  I'm assuming it's sensor tilt, but who knows.  I'm hoping that Gaston's new version will help me determine the issue.

 

Ron


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#434 KTAZ

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Posted 20 May 2024 - 10:33 AM

I agree with your experience.  It took a few trials and errors to get the image just right... orientation, exposure, focus setting, etc., but now it's pretty easy.  I was surprised at how a very small change makes such a big difference... particularly with my HyperStar.  That thing is very, very sensitive.

 

Now I'm wrestling with another problem with the HyperStar.  The center stars are very good, but the out-lying stars... not so much.  I'm assuming it's sensor tilt, but who knows.  I'm hoping that Gaston's new version will help me determine the issue.

 

Ron

Yes, tilt will be my next focus. I already have a CTU in the imaging train, and had adjusted it before, but Gaston is right that we should get the collimation nailed before moving on the tilt adjustments.

 

However, backfocus is the second step after the collimation. In particular, the Celestron Edge HD reducers will impart some CA to stars if this isn't dead on. I will then move on to tilt. Then I plan to go in reverse order; verify tilt is good, check the back focus one more time, then check the collimation one more time.


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#435 RonaldNC

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Posted 20 May 2024 - 01:34 PM

Yes, tilt will be my next focus. I already have a CTU in the imaging train, and had adjusted it before, but Gaston is right that we should get the collimation nailed before moving on the tilt adjustments.

 

However, backfocus is the second step after the collimation. In particular, the Celestron Edge HD reducers will impart some CA to stars if this isn't dead on. I will then move on to tilt. Then I plan to go in reverse order; verify tilt is good, check the back focus one more time, then check the collimation one more time.

Not to derail this thread too much... but using "correct only" with BlurXterminator in PixInsight as a first step is a game changer.  I am amazed how it corrects deformed stars.

 

Ron



#436 KTAZ

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Posted 20 May 2024 - 01:39 PM

Not to derail this thread too much... but using "correct only" with BlurXterminator in PixInsight as a first step is a game changer.  I am amazed how it corrects deformed stars.

 

Ron

I'm waiting on Russ to release "CollimationXterminator"...

 

Then we're all set...lol.gif


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#437 KTAZ

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Posted 17 June 2024 - 02:16 PM

I made the investment in Skywave and have some issues ATM. I might be using it incorrectly or folowing the wrong steps.

 

Initially, I spent 2 hours tweaking my 9.25 Edge SCT with .70 reducer. I ended up with a score around 8.9 and said "good enough". Unfortunately, my star shapes are elongated. Double checked my balance, PA, tilt, etc., and all were dialed in very tight. Tracking was around .50 in PHD2.

 

I made a second attempt and cannot even get it close now. I am able to get the coma adjusted to a 10, but that makes the astig drop into the red zone. If I get the astig close, maybe into the yellow zone, the coma goes back out of the green zone. It is like ping pong with adjusting for the astig; it bounces from one side of the red ring to the other with only minor adjustments.

 

HELP. Any tips or suggestions would be appreciated.



#438 KTAZ

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Posted 18 June 2024 - 11:56 AM

I made the investment in Skywave and have some issues ATM. I might be using it incorrectly or folowing the wrong steps.

 

Initially, I spent 2 hours tweaking my 9.25 Edge SCT with .70 reducer. I ended up with a score around 8.9 and said "good enough". Unfortunately, my star shapes are elongated. Double checked my balance, PA, tilt, etc., and all were dialed in very tight. Tracking was around .50 in PHD2.

 

I made a second attempt and cannot even get it close now. I am able to get the coma adjusted to a 10, but that makes the astig drop into the red zone. If I get the astig close, maybe into the yellow zone, the coma goes back out of the green zone. It is like ping pong with adjusting for the astig; it bounces from one side of the red ring to the other with only minor adjustments.

 

HELP. Any tips or suggestions would be appreciated.

Ok, I went back through the training videos and from what I can ascertain ONLY the coma is important when adjusting an SCT. If spherical is also OK, then the astig is just what is is.

 

Am I correct in this?



#439 Corsica

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Posted Yesterday, 02:48 PM

Ok, I went back through the training videos and from what I can ascertain ONLY the coma is important when adjusting an SCT. If spherical is also OK, then the astig is just what is is.

 

Am I correct in this?

You are correct that SCTs EdgeHD have a spherical secondary mirror. For alignment (collimation) of both mirrors, all you need to monitor is coma for an on-axis (at the center of the camera's chip) defocused star.

Here are a few points to consider:

 

1. Ensure that you do not clip (saturate) the image. Any hot/dead pixels are automatically handled by the SKW pre-processing. We recommend aiming for half to 2/3 of the maximum ADU using at least a 16-bit FITS file format (float format is fine). All the images must be monochrome FITS files.

 

2. Due to seeing conditions, you may want to use a long enough exposure time, at least 10 seconds or so. You could use longer exposures at the end of the collimation for higher accuracy. SKW's engine is a wavefront sensor, which means that it will measure the wavefront distortion from the optics and the atmospheric turbulence. The latter contribution decreases as integration time gets longer.

 

3. When coma is canceled on-axis, you should have a minimum of astigmatism, at least inside the corrected circle of the scope (where you are diffraction-limited) and none on-axis. If you see some astigmatism, there are two likely explanations:

 

-a- Tracking drift during the exposure: Keep in mind that the diffraction limit is around 0.075 wave RMS, which is not that much. At that level of wavefront error, you will not stop the defocused star elongation by just human inspection; this is too little to see. This also means that very little drift leading to an elongated star (not from any aberration) may be reported as astigmatism. If exposures of 10 seconds or more are an issue, you could use shorter exposures and either stack time (using an auto-correlation algorithm, not centroid) or just look on SKW at the center of the score cluster (blue dot) to estimate the average astigmatism value (enable the scatter plot option in SKW collimator tool).
  
-b- Astigmatism off-axis is expected but not on-axis: If tracking drift is not the source, you may have some tilt in the optical train, or even at the level of the field lens (corrector). I would assume that the optical surfaces themselves are near perfect.


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#440 KTAZ

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Posted Yesterday, 03:15 PM

Thanks much, Gaston. I do see some tilt that is showing up after the collimation, so that is very likely the source.

 

I do appreciate the feedback!




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