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Tele Vue 31mm Nagler eyepiece question

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#1 jkevn

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Posted 18 September 2019 - 03:49 PM

I am buying a 31mm Nagler eyepiece, to be used in a Celestron 11" EdgeHD. I have a Baader clicklock visual back and a 2" Televue diagonal that has a light path length of 3 ½". Should I attach the diagonal to the 1 ¾" long Baader clicklock, or a longer visual back to avoid possible vignetting problems? I know that for the 11" EdgeHD the ideal back focus distance is 5 3/4", but I understand this is important mainly for imaging, not visual.

 

Does anyone have experience using the 31mm Nagler eyepiece? Do you like it?



#2 Neptune

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Posted 18 September 2019 - 03:54 PM

I don't think you will have a problem with vignetting. I have the same basic setup.  The field stop of the 31mm Nagler is 42mm the largest in a 2" eyepiece is approx. 46mm.



#3 SeattleScott

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Posted 18 September 2019 - 05:50 PM

I wouldn’t worry about it. One guy used a 40mm swa with a focal reducer on his C11.

#4 areyoukiddingme

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Posted 18 September 2019 - 07:36 PM

I used the 31 Nagler when I had an 11” edgehd. I used the Astro-physics visual back with a Televue diagonal with excellent results. I think the optimal spacing really only applies for critical planetary viewing, especially if you are using binoviewers


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#5 Roragi

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Posted 19 September 2019 - 03:21 AM

Many are going to put their hands to the head, but from my point of view I do not like this eyepiece. In my configurations I have only borrowed a friend to use in the refractor when an object is too large and I want to use it with a filter. 

In the Newton the exit pupil is excessive and I do not see any reason for purchase, my cap is 21mm. The position of the eye bothers me, I can't focus my eyes well, horrible.



#6 Jon Isaacs

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Posted 19 September 2019 - 04:33 AM

Many are going to put their hands to the head, but from my point of view I do not like this eyepiece. In my configurations I have only borrowed a friend to use in the refractor when an object is too large and I want to use it with a filter. 

In the Newton the exit pupil is excessive and I do not see any reason for purchase, my cap is 21mm. The position of the eye bothers me, I can't focus my eyes well, horrible.

The scope in question is an F/10 SCT so the exit pupil will only be 3.1 mm.  

 

I have a 31mm Nagler that I use extensively in my various Dobs, including my 12.5 inch F/4.06, mostly I use it with a Paracorr but not always.  For some the exit pupil may exceed the diameter of their dark adapted pupil... It's an eyepiece that should be used with a coma corrector in a faster Newtonian, the view is just so perfect.  

 

But the question here is about an SCT and back focus.  

 

Jon



#7 Roragi

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Posted 19 September 2019 - 05:11 AM

The scope in question is an F/10 SCT so the exit pupil will only be 3.1 mm.  

 

I have a 31mm Nagler that I use extensively in my various Dobs, including my 12.5 inch F/4.06, mostly I use it with a Paracorr but not always.  For some the exit pupil may exceed the diameter of their dark adapted pupil... It's an eyepiece that should be used with a coma corrector in a faster Newtonian, the view is just so perfect.  

 

But the question here is about an SCT and back focus.  

 

Jon

Hi Jon,

 

In my situation, I have tested it with my 16" f4 with integrated Sips paracorr, 31mm / f4 = 7.75mm exit pupil. It is not pleasant, maybe with the use of the filter I can tolerate it somewhat but as I said previously the position of the eye is very uncomfortable for me, it is a very thick eyepiece, On the other hand the E 21 is perfect in all its senses.


Edited by Roragi, 19 September 2019 - 05:12 AM.


#8 Jon Isaacs

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Posted 19 September 2019 - 02:13 PM

In my situation, I have tested it with my 16" f4 with integrated Sips paracorr, 31mm / f4 = 7.75mm exit pupil.

 

 An F/4 with the Parcorr is operating at 4.6 and the exit pupil with the 31mm Nagler 31mm/4.6 = 6.6mm.  

 

At such large exit pupils, it is likely that it's the inherent astigmatism in your own eye you are seeing rather than in the eyepiece/telescope.  I happen to have a large dark adapted pupil and zero correction for astigmatism and I see sharp stars right to the edge with the Paracorr 2.  There is slight vignetting.  

 

But again, this is not about the 31mm Nagler at F/4 or F/4.6, it's about the 31mm Nagler in an F/10 Edge with a 3.1mm exit pupil and the proper spacing of the eyepiece.  

 

Jon


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#9 Roragi

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Posted 20 September 2019 - 12:15 AM

Hi again, F 4.6? As I calculated this, I'm curious. The paracorr increases 1.15x. Only my personal opinion, I have not tried this eyepiece in a C11 but in my scope it is horrible.



#10 scotsman328i

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Posted 20 September 2019 - 05:20 AM

Many are going to put their hands to the head, but from my point of view I do not like this eyepiece. In my configurations I have only borrowed a friend to use in the refractor when an object is too large and I want to use it with a filter. 

In the Newton the exit pupil is excessive and I do not see any reason for purchase, my cap is 21mm. The position of the eye bothers me, I can't focus my eyes well, horrible.

TeleVue cult followers come in waves with torches and pitchforks in T Minus 5...4...3...2...1...



#11 Jon Isaacs

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Posted 20 September 2019 - 05:38 AM

Hi again, F 4.6? As I calculated this, I'm curious. The paracorr increases 1.15x. Only my personal opinion, I have not tried this eyepiece in a C11 but in my scope it is horrible.

You said your scope is F/4.  Add the Paracorr:  F/4  x 1.15 = F/4.6  

 

I don't know what is horrible about it, I have never had anyone look through the 31mm with a Paracorr or in a refractor and not be amazed.  Maybe you could explain what you are seeing.  

 

Jon


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#12 Roragi

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Posted 20 September 2019 - 05:52 AM

Well, I find it hard to put the eye in the correct position and I have many blackouts, I notice that this eyepiece is too thick, it also has a lot of curvature, everything above looks curved and in the lower part the same but with different parabola, in addition to the aforementioned a lot of pupil Well I don't want to dirty the post anymore, if anyone can add their experiences with N31 + C11.


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#13 Jon Isaacs

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Posted 20 September 2019 - 06:10 AM

Well, I find it hard to put the eye in the correct position and I have many blackouts, I notice that this eyepiece is too thick, it also has a lot of curvature, everything above looks curved and in the lower part the same but with different parabola, in addition to the aforementioned a lot of pupil Well I don't want to dirty the post anymore, if anyone can add their experiences with N31 + C11.

 

I will just add that the curvature you are talking about is pincushion distortion and not a curved focal plane.  The eyepiece positioning issue could be related to the diameter of your dark adapted pupil versus the exit pupil. I have never experienced blackouts with this eyepiece but I never do with any eyepiece except during the day when my pupil is not dilated.  My pupil is quite large.

 

That said, yes, it's time to discuss the 31mm in the C-11.

 

Jon




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