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Best barlow for a Nagler 13T6

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#1 Adam Long

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Posted 20 November 2019 - 05:28 AM

I was considering buying a 5-6mm wideangle eyepiece when I realised I should be able to achieve something similar by barlowing my 13mm Nagler.

 

The only Barlow I have is the little screw-on 2.25x Baader Hyperion intended to be used with the BH zoom. It's not an enjoyable combo with the Nagler - you can't see the full field and the edges are blurred.

 

Has anyone had a better experience with other barlows? Guessing a powermate would be better but that's more $$$ than a Meade 5.5mm UWA or ES 6.7/82...


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#2 astrophile

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Posted 20 November 2019 - 06:04 AM

You might try an older used TeleVue 2.5x barlow. OPT appears to have one available.

#3 TOMDEY

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Posted 20 November 2019 - 08:18 AM

The TeleVue PowerMate is the only way to eliminate the vignetting you are experiencing... which is due to the inexorable exit pupil back-shift caused  by ~regular~ barlows.    Tom



#4 Jon Isaacs

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Posted 20 November 2019 - 08:28 AM

The TeleVue PowerMate is the only way to eliminate the vignetting you are experiencing... which is due to the inexorable exit pupil back-shift caused  by ~regular~ barlows.    Tom

 

The vignetting is caused by the limited clear aperture of the Baader zoom, it's only 13.2 mm.

 

https://agenaastro.c...oom-barlow.html

 

The 13mm Nagler has a 17.6 mm field stop.. vignetting cannot be avoided.

 

I have a 2X 1.25 inch TV Barlow, it works well with the 13mm Type 6 Nagler. Its longer than a shorty Barlow but not too long.. I suspect the 2.5x TV Barlow that John suggested would be a good choice as well.

 

Jon


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#5 Adam Long

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Posted 20 November 2019 - 09:13 AM

Thanks for the help. I guess there's no escaping the exit pupil problem without ponying up for a Powermate. But looks like a bigger clear aperture might be a start.



#6 esd726

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Posted 20 November 2019 - 10:03 AM

I think my 2x ES Focal Extender works great with my 13 T6.  


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#7 dan_h

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Posted 20 November 2019 - 10:14 AM

Thanks for the help. I guess there's no escaping the exit pupil problem without ponying up for a Powermate. But looks like a bigger clear aperture might be a start.

 

I don't think the exit pupill thing would be a problem here.  The 13T6 doesn't have an exceptionally long eye relief to start with and adding a little to it may very well be an advantage.  

 

I use my 13T6 with a three element Antares 2X Barlow which is apparently the same as the Celestron Ultima.  I have never noticed any issues but I don't Barlow a lot as I also have a 7T6 in my kit. 

 

https://www.cloudyni...-some-thoughts/

 

dan


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#8 F.Meiresonne

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Posted 20 November 2019 - 01:52 PM

The vignetting is caused by the limited clear aperture of the Baader zoom, it's only 13.2 mm.

 

https://agenaastro.c...oom-barlow.html

 

The 13mm Nagler has a 17.6 mm field stop.. vignetting cannot be avoided.

 

I have a 2X 1.25 inch TV Barlow, it works well with the 13mm Type 6 Nagler. Its longer than a shorty Barlow but not too long.. I suspect the 2.5x TV Barlow that John suggested would be a good choice as well.

 

Jon

I agree, a TV2 is a very good Barlow. Love it. But i cannot use it in my diagonals, she might hit the mirror.



#9 F.Meiresonne

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Posted 20 November 2019 - 01:53 PM

I don't think the exit pupill thing would be a problem here.  The 13T6 doesn't have an exceptionally long eye relief to start with and adding a little to it may very well be an advantage.  

 

I use my 13T6 with a three element Antares 2X Barlow which is apparently the same as the Celestron Ultima.  I have never noticed any issues but I don't Barlow a lot as I also have a 7T6 in my kit. 

 

https://www.cloudyni...-some-thoughts/

 

dan

Indeed, exactly my thinking too



#10 SteveG

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Posted 20 November 2019 - 03:19 PM

I don't think the exit pupill thing would be a problem here.  The 13T6 doesn't have an exceptionally long eye relief to start with and adding a little to it may very well be an advantage.  

 

I use my 13T6 with a three element Antares 2X Barlow which is apparently the same as the Celestron Ultima.  I have never noticed any issues but I don't Barlow a lot as I also have a 7T6 in my kit. 

 

https://www.cloudyni...-some-thoughts/

 

dan

I use my 13T6 with a Celestron Ultima barlow for my travel kit. It does not vignette, and in fact it works very well. The barlow actually magnifies about 2.2x, so I figure it becomes a 6 mm Nagler.

 

I have read very good reports on the new Celestron shorty:

https://bhpho.to/2QMTEpZ


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#11 SteveG

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Posted 20 November 2019 - 03:21 PM

I agree, a TV2 is a very good Barlow. Love it. But i cannot use it in my diagonals, she might hit the mirror.

Which diagonals? Almost all 1.25" diagonals have an internal ring stop.


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#12 havasman

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Posted 20 November 2019 - 06:07 PM

Thanks for the help. I guess there's no escaping the exit pupil problem without ponying up for a Powermate. But looks like a bigger clear aperture might be a start.

Either the TV 2x Barlow or the Celestron Ultima 2x Barlow should work fine. Neither are Powermates and both are less expensive. If your system contains a 2" diagonal you have to check clearance and you may need a "hi-hat" 2"-to-1.25" adapter to provide clearance.

IMO, best long-term satisfaction is via discreet focal length eyepiece.


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#13 Adam Long

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Posted 21 November 2019 - 08:00 AM

Thanks folks. I've found a good deal on a used Celestron Ultima SV so will give that a go and report back...

 

Both scopes are dobs so no diagonal issues.


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#14 F.Meiresonne

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Posted 21 November 2019 - 12:43 PM

Which diagonals? Almost all 1.25" diagonals have an internal ring stop.

Really , i got to check this then, it a TS 2 inch diagonal with 1.25 adapter,91% reflection,not the highest quality allthough i really see no difference if i use my TS 1.25 diagonal with 99% reflection.


Edited by F.Meiresonne, 21 November 2019 - 12:45 PM.


#15 SteveG

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Posted 21 November 2019 - 01:27 PM

Really , i got to check this then, it a TS 2 inch diagonal with 1.25 adapter,91% reflection,not the highest quality allthough i really see no difference if i use my TS 1.25 diagonal with 99% reflection.

I’m not as familiar with the TS products. I would carefully measure how far the 1.25” barlow protrudes into the 2” diagonal. I’ve not had one interfere yet, using (2) different 2” diagonals and (5) different barlows.


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#16 F.Meiresonne

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Posted 21 November 2019 - 03:46 PM

I’m not as familiar with the TS products. I would carefully measure how far the 1.25” barlow protrudes into the 2” diagonal. I’ve not had one interfere yet, using (2) different 2” diagonals and (5) different barlows.

yes indeed , so that is why , in rare cases now ,i use a TAL 2x Barlow because it is short, sharpness a bit less then the TV2 but great contrast and pretty  dark..

 

But i will check the ring ...



#17 nicoledoula

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Posted 21 November 2019 - 07:14 PM

Buy and install an O-ring to protect your diagonal glass from being touched. 




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