1. Final Announcement: We're Saying Goodbye to AstronomyConnect. Read Our Closing Notice.
Dismiss Notice
New Cookie Policy
On May 24, 2018, we published revised versions of our Terms and Rules and Cookie Policy. Your use of AstronomyConnect.com’s services is subject to these revised terms.

Prism diagonals

Discussion in 'Eyepieces, Barlows, and Filters' started by Gabby76, Aug 16, 2023.

Prism diagonals

Started by Gabby76 on Aug 16, 2023 at 9:31 PM

3 Replies 633 Views 2 Likes

Reply to Thread Post New Thread
  1. Gabby76

    Gabby76 Well-Known Member

    Joined:
    Dec 16, 2016
    Posts:
    568
    Trophy Points:
    63
    Location:
    Slovakia
    Prism diagonals can be a handy accessory when you are in a situation that requires more drawtube travel.
    1.25" prisms have the shortest lightpath when compared to mirrors and a 2" prism lightpath falls between a 1.25"and 2" mirror. This can get you into focus without adapters or extension pieces.

    The issue with using a prism is that if the telescope is not made for prism use it can actually degrade the views.

    So how do you find out if a prism will work with your refractor? Keep reading and I will explain :)

    Once you are set up use a mirror diagonal and a high power eyepiece, something that will get at least 50x per inch of aperture. You may need to use a barlow. A 6mm with 2x barlow will give 59x with a 102 f/7

    Aim your telescope at a bright star and defocus inwards. Look at the first ring around the airy disk. If it has a red/ orange/ pink tint to it a prism will work with your telescope.
    If the ring remains white then a prism will not work with your telescope.

    Hopefully this quick test will save some people money.
     
    Ed D and sojourneyer like this.
  2. sojourneyer

    sojourneyer Well-Known Member

    Joined:
    Oct 17, 2020
    Posts:
    183
    Trophy Points:
    43
    That is very interesting Gabby. Thanks for sharing this information

    As an aside I read something about prism diagonals being better than a mirror diagonal for reflectors or vice versa.:(
     
  3. Ed D

    Ed D Well-Known Member

    Joined:
    Jan 12, 2017
    Posts:
    855
    Trophy Points:
    93
    Location:
    Sunny South Florida
    Thank you for the very useful information.

    I have always had both types of diagonals. I use mirrors for observing deep space and prisms for planetary and lunar observation. This in both my refractors and Maks.

    Ed
     
    Gabby76 and sojourneyer like this.
  4. Gabby76

    Gabby76 Well-Known Member

    Joined:
    Dec 16, 2016
    Posts:
    568
    Trophy Points:
    63
    Location:
    Slovakia
    Prisms and mirrors are both tools in the toolbox so to speak.
    I must say that I tend to use mine in the same way Ed.
     
    Ed D and sojourneyer like this.

Share This Page