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?
If using a Paracorr is there any benefit to using a coma correcting Barlow?
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
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.
- Vic Menard, Jeff Struve and Blueox4 like this
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.