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use of Barlow on a 14 inch Cestron Cassegranian

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#1 michael mckinney

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Posted 04 December 2022 - 05:01 PM

Oh learned ones, Oh brothers and sisters of the guild, quench my ignorance with the calm steely eyed reserve of your respected knowledge.


I have a 22 inch Dob with a 100 inch focal length and a Teleview binoviewer. It has a 2X amplifier (BARLOW) attached so when I use 24 mm old style Teleview widefield eyepiece I'm getting a magnification of 200 because of the attached 2X Barlow. I get good planetary views but I want more magnification. I see C 14 for sale with a focal length of 154 inches. If I used my binoviewer with the Barlow attached would I get a magnification of 308? In other words can I use the 2X Barlow on the C 14? I want around 400X or more with a comfortable view. Would I be better off buying two widefield 12MM eyepieces and fit them to my Dob?

#2 ngc7319_20



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Posted 04 December 2022 - 06:20 PM

You could add another 2x Barlow in the optical chain with the Dob.  For example, a 2" 2x Barlow ahead of the BinoVue.  That might be the cheapest solution.  And it would preserve the comfort of the TV 24 Wide Fields.


A pair of ~12mm eyepieces is another solution.  


The C14 would also work.  And your current bino setup with the 2x should be fine with it. But it is a larger investment, and a new bunch of equipment to learn and troubleshoot.

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#3 Eddgie



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Posted 04 December 2022 - 07:12 PM

Better would be to get a Televue 4x PowerMate and continue to use our current telescope. You can get PowerMates in a variety of powers. 


Be aware that the 1.25" 2.5x PowerMate only gives about 2.1x when used with binoveiwers.  Best to get the 4x. It will maintain close to 4x when used with a binoviewer..

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#4 12BH7



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Posted 04 December 2022 - 09:17 PM

Your scope has 2540mm of focal length with another 150mm added for the binoviewer. This gives you a total FL of roughly 2690mm with the BV. 


2690mm / 24mm = 112x power

112 x 2 (Barlow)  = 224x power


Adding a

3x Barlow would give 336x

4x Barlow would give 448x


Being an avid  BV user, there is a limit on magnification and image quality.  What I've found is that there is a sweet spot between magnification and a good workable image with a BV.   I would first try a 3x and see how the image holds. Then up it to 4x or even 5x if it's working out.


Not having any experience with a 22 inch scope, you're going to have to find at what point the image is more degraded then it's worth. For me using a 12" SCT that is around 170x. After that the image is just big and lacking any useful detail. 

Edited by 12BH7, 04 December 2022 - 09:17 PM.

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