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

Null test image of 90s era C11

  • Please log in to reply
5 replies to this topic

#1 Darren Drake

Darren Drake

    Skylab

  • *****
  • topic starter
  • Posts: 4,380
  • Joined: 09 Oct 2002
  • Loc: Chicagoland

Posted 03 December 2021 - 03:37 PM

A friend recently got a used C11 settup and brought it over to evaluate the optics.  Using my excellent 12.5 inch Discovery to produce a collimated star we got an image that showed a bit of overcorrection but with a relatively smooth surface.   Then we took out the 2 inch diagonal and got a near perfect null but with radial spokes.  These I suspect are ground into the primary as a result of print through from the back of the mirror.  In any event it is an excellent overall sct optically.  The best result is without the diagonal unfortunately but still with it it is fairly good.

Attached Thumbnails

  • IMG_20211203_21288.jpg
  • Screenshot_20211202-204857_Video Player.jpg

Edited by Darren Drake, 03 December 2021 - 03:40 PM.

  • cookjaiii likes this

#2 cookjaiii

cookjaiii

    Apollo

  • *****
  • Posts: 1,157
  • Joined: 23 Nov 2015
  • Loc: Southeast PA, 10mi north of Philadelphia

Posted 03 December 2021 - 04:43 PM

Is there a written description of the "collimated star" set up that you could point me to?  Thank you.



#3 Borodog

Borodog

    Soyuz

  • *****
  • Posts: 3,771
  • Joined: 26 Oct 2020

Posted 03 December 2021 - 05:19 PM

Yes I'd be very interested in a description of exactly what you're doing here.



#4 Darren Drake

Darren Drake

    Skylab

  • *****
  • topic starter
  • Posts: 4,380
  • Joined: 09 Oct 2002
  • Loc: Chicagoland

Posted 03 December 2021 - 05:23 PM

Yes actually I wrote an article here on this many years ago...

https://www.cloudyni...null-test-r1586


  • Borodog likes this

#5 Darren Drake

Darren Drake

    Skylab

  • *****
  • topic starter
  • Posts: 4,380
  • Joined: 09 Oct 2002
  • Loc: Chicagoland

Posted 03 December 2021 - 05:59 PM

Today I use a focuser insertable artificial star with stacked barlows to produce a disk that's about 2.5 arcseconds across.  That's good enough to do some revealing star and null tests in my basement...

Attached Thumbnails

  • IMG_20211203_16308.jpg


#6 cookjaiii

cookjaiii

    Apollo

  • *****
  • Posts: 1,157
  • Joined: 23 Nov 2015
  • Loc: Southeast PA, 10mi north of Philadelphia

Posted 03 December 2021 - 10:08 PM

Thanks!




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