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

If using a Paracorr is there any benefit to using a coma correcting Barlow?

  • Please log in to reply
3 replies to this topic

#1 Blueox4

Blueox4

    Viking 1

  • *****
  • topic starter
  • Posts: 518
  • Joined: 26 Nov 2015
  • Loc: Upstate New York

Posted 22 January 2020 - 05:34 AM

If you have a Paracorr 2 in your Dob is there any benefit or negative to using a coma correcting Barlow such as the APM 2.7 CC Barlow in the Paracorr? It seems like they do the same thing. The Barlow is optimized for F/4. My incoming Dob will be f/4 so I’m wondering if the Barlow will compliment views in the Paracorr or is not needed because I have a Paracorr? 



#2 happylimpet

happylimpet

    Skylab

  • *****
  • Posts: 4,324
  • Joined: 29 Sep 2013
  • Loc: Southampton, UK

Posted 22 January 2020 - 05:53 AM

it shouldnt be needed. If anything, it should make the views worse by correcting an issue which isnt there.


  • Jon Isaacs, Jeff Struve and Blueox4 like this

#3 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 81,829
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 22 January 2020 - 07:55 AM

At F/4, the Paracorr 2 fully corrects the coma a field of view larger than the 31mm Nagler..

 

A coma correcting Barlow would only add more reverse coma which would have a negative effect, it would be like using the coma correcting Barlow in a refractor or other scope corrected for coma.  

 

I have never used the coma correcting Barlow but I've been suspicious about how well they might work.  Historically, the myth that a Barlow corrects for coma has been around the internet forever.   If it doesn't have have a way to adjust the spacing, then that's a red flag for me.

 

Jon


  • Vic Menard, Jeff Struve and Blueox4 like this

#4 Starman81

Starman81

    Soyuz

  • *****
  • Moderators
  • Posts: 3,712
  • Joined: 06 Mar 2008
  • Loc: Metro Detroit, MI, USA

Posted 23 January 2020 - 10:52 AM

I struggle to think of a use case for a coma correcting barlow. If coma in your newt bothers you, then you probably already have a coma corrector... Is it to allow barlow usage without having to use the coma corrector while still retaining coma correction? That would make for a smaller optical stack.




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