Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

SkyWave wave front analyser questions from a newby.

  • Please log in to reply
3 replies to this topic

#1 George P Dunham

George P Dunham

    Viking 1

  • -----
  • topic starter
  • Posts: 773
  • Joined: 24 Jun 2012
  • Loc: Crawford,CO USA

Posted 21 April 2021 - 12:59 PM

I am just starting to use SkyWave for collimation.  Remarkable software.  I have a few questions if there some users out there.

1. Using a OSC camera.  I am taking pictures that I hope are within the parameters set by the software.  I use nebulocity to extract the red channel and use that for the wave analysis.  I have not been able to find a way to get live images analysed and I am under the impression that I should be able to.  Can someone clarify?  My initial results are very ugly but that was expected.

2. If I need a live feed from my SX25C camera in monochrome, can the raw undebayered image be used or do I have to do something like use a filter (all I have are NB filters.  Can I use one of those?) and change the raw fits to a debayered fits? 

3. I use a ASI1600MM pro for the autoguide camera. Should I swap the ASI1600MM pro for the SX25C OSC camera?  I was hoping to avoid such a labor intensive undertaking.

4. I experimented last night and have 4 exposures of the same star and same settings.  They give me 4 different solutions.  They are 10 second exposures.  Is this purely seeing?  Do I need to make these longer like 20 seconds or more?

5. I am using a C14 EdgeHD in which I removed the corrector a few years ago for cleaning.  I noted a trefoil aberration and I am wondering if I might have tightened the set screws too tight when I returned the corrector.  What are your thoughts?

6. I have a Optec FastFocus so I have no spider but I have a thin cable from the secondary fastfocus to the edge of the tube.  It is not a straight line but slightly curved and runs at a small angle from perpendicular from the optical axis.  Will this confuse the solution?

 

More later.

Thanks in advance.


Edited by George P Dunham, 21 April 2021 - 02:35 PM.


#2 LauraMS

LauraMS

    Ranger 4

  • -----
  • Posts: 361
  • Joined: 29 Mar 2011
  • Loc: Germany

Posted 22 April 2021 - 12:49 AM

I don't have the SkyWave  but some experience with seeing measurements.

 

4. The seeing can vary considerably over 10 seconds.  As you want to use the SkyWave to assess your telescope you need to intent to get as stable seeing as possible - longer exposure time, and stacking multiple images from several minutes such that seeing effects cancel out. That's what I would try. Check earlier posts on WinRoffier Software - it did the same as SkyWave but with other methods, but that may give you some hint.

 

5. TreFoil can have different sources. Tyically it is pinched optics. In a SCT it may be the corrector plate which may be the case here because you mentioned it had been removed earlier. You say it is an Edge - maybe one or more of the corrector plate adjustment screws are too tight. They should just fix the corrector plate but not exert pressure on it. Loosen each one and then gently fix it again without pressure. Observe in the SkyWave what happens.

If its not the corrector plate fixation check the holding ring which keeps the corrector plate from falling out of the tube. None of the screws should be too tighened as well. Check with SkyWave if things have improved after gently relaxing them in way that the corrector plate is prevented from falling out.

 

If not improved after that is done, you may rotate the corrector plate by small amounts like 30-45° to see if the pattern has rotatet as well. Then it would be the corrector plate or secondary. Otherwise it would be somewhere else in your Edge, e.g. in the corrector lenses in the baffle, or later in your optical train.

 

But I guess the corrector plate is the key part you should concentrate in on the beginning. It is easy to make something wrong here, e.g. after removing it inserting it not with the mark at the side of the corrector plate at the 3 hour position.

 

To elimiate the cable from the Optec front focuser can you temporarily remove it.Just to make shure it has no significant influence. It certainly causes asymmetric diffraction but I wouldn't expect it so severe that it shows significant trefoil. How huch trefoil do you have ? It would be interesting to see your data.

 

Good luck!

Laura



#3 George P Dunham

George P Dunham

    Viking 1

  • -----
  • topic starter
  • Posts: 773
  • Joined: 24 Jun 2012
  • Loc: Crawford,CO USA

Posted 22 April 2021 - 12:37 PM

I appreciate your reply.  I am looking for SkyWave specific user directions.



#4 George P Dunham

George P Dunham

    Viking 1

  • -----
  • topic starter
  • Posts: 773
  • Joined: 24 Jun 2012
  • Loc: Crawford,CO USA

Posted 24 April 2021 - 11:09 AM

After spending some time and developing a work flow, I have answered most of my own questions.  At one point in my alignment process I achieved a status of "good" per software.  My trefoil aberration whet to nearly zero as did other other aberrations.  So I consider this thread completed.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics