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

SCT collimation with APT

  • Please log in to reply
4 replies to this topic

#1 Ken82

Ken82

    Explorer 1

  • -----
  • topic starter
  • Posts: 73
  • Joined: 29 Jan 2017

Posted 31 October 2019 - 08:17 AM

Trying the get the best possible collimation on my 11”edge hd using the collimation tool in APT. Has anyone else been using this ? Does my image look about right ? 
 

I collimated it visually first and then set up the camera centred the star and it looks good to me ? 

Attached Thumbnails

  • A091A1A8-B9E6-459B-81D6-9E35B3EF90C2.jpeg


#2 Poochpa

Poochpa

    Surveyor 1

  • *****
  • Posts: 1,848
  • Joined: 12 Feb 2005
  • Loc: Buffalo Burbs, NY

Posted 31 October 2019 - 08:35 AM

Hi Ken,

The star you’re using is way overexposed. You need to see the defocused diffraction rings, so use a dimmer star or reduce your exposure, gain, or iso. See the sample image used in the APT User Guide for the collimation aid.

Mike


  • Kegan128 and AJK 547 like this

#3 Ken82

Ken82

    Explorer 1

  • -----
  • topic starter
  • Posts: 73
  • Joined: 29 Jan 2017

Posted 05 November 2019 - 08:15 AM

Thanks Mike I’ve had a further look and changed exposure down plus kept binning to 1x1 and gain 90. But although the image is much nearer to the APT one with the diffraction rings I’m just not able to get the rings to show on screen. I found it much easier with an eye piece but that clearly won’t work for imaging. 

I tried multiple different exposures, gain and binning but the closest I could get is this image -

 

any tips would be great !

  
 

Attached Thumbnails

  • 87634703-BF57-4241-9511-C4D896B773DB.jpeg


#4 Poochpa

Poochpa

    Surveyor 1

  • *****
  • Posts: 1,848
  • Joined: 12 Feb 2005
  • Loc: Buffalo Burbs, NY

Posted 05 November 2019 - 12:27 PM

No reason you can't collimate with the eyepiece and see how your subs look when imaging. Also, what your showing above is usable for collimation. I see the offset is towards the 3 o'clock position. The first dark diffraction ring thins on that side. Turn the appropriate screw to move the offset the opposite way. You know your turning the screw the correct way if the entire star moves in the direction of the thicker part. Make sure you recenter the star. Alternatively, to improve the definition of the diffraction rings, use a brighter star and/or a star at higher altitude. You may have to wait for a night of better seeing.

 

Finally, I've been using a tri-bahtinov mask for collimation when imaging for the past 3 years and it works great. Here's a link to the mask generator to have one made:

https://github.com/c...rain-Telescopes

 

Here's before and after images of the collimation of my 9.25" using a tri-B mask:

Tri-B Image Before Collimation.jpg

Tri-B Image After Collimation.jpg

 

Mike


Edited by Poochpa, 05 November 2019 - 12:28 PM.


#5 macdonjh

macdonjh

    Aurora

  • *****
  • Posts: 4,696
  • Joined: 06 Mar 2006

Posted 05 November 2019 - 01:08 PM

 You may have to wait for a night of better seeing.

 

+1

 

You may have to be patient.  When I initially collimated my C11 I ended up tweaking collimation over the course of six months or so.  I got close the first night in bad seeing.  then I checked each night I observed, just looked at my last alignment star.  If the defocused image made me think seeing was better than the last time I was out, I tweaked.  If seeing was worse, I started observing.  After five or six iterations of that I had collimation dialed in as well as I could.  After that I checked every few months to be sure I was still good.




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