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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. 



#18 Adam Long

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Posted 09 December 2019 - 08:03 AM

So... the 13T6 gives a nice sharp view with the Celestron Ultima SV 2x, but is quite heavily vignetted. The barlow doesn't vignette my Meade 5.5mm UWA or ES 26/62.

 

I use my 13T6 with a Celestron Ultima barlow for my travel kit. It does not vignette, and in fact it works very well.

Guessing this must be a different model?



#19 Starman1

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Posted 09 December 2019 - 02:34 PM

Vignetting isn't directly related to the clear aperture of the Barlow, but how the focal length of the barlow lens results in a light cone entry into the eyepiece.

I found the Baader VIP barlow a good match for the T6 Naglers, optically.

Though, I generally find telecentric barlows like the PowerMates a bit less of a problem to use because the distance between eyepiece and lens isn't important.



#20 YAOG

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Posted 09 December 2019 - 02:47 PM

I'm a fan of the TeleVue PowerMates, I used to use them a lot but as the collection filled out to include more discreet eyepieces, not so much. They work very well with the Panoptic and T6 Naglers I have.  


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#21 Jon Isaacs

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Posted 09 December 2019 - 03:00 PM

I am sure the Powermates work well with the T-6 Naglers.  I use a 1.25 inch 2X TeleVue Barlow and it works very nicely.  It's not a shorty and it's not an old style long Barlow, it's a mid length Barlow that also happens to be parfocal. 

 

Jon



#22 SteveG

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Posted 09 December 2019 - 03:40 PM

So... the 13T6 gives a nice sharp view with the Celestron Ultima SV 2x, but is quite heavily vignetted. The barlow doesn't vignette my Meade 5.5mm UWA or ES 26/62.

 

Guessing this must be a different model?

Mine is the original Celestron Ultima 2x barlow (shorty, 3-element). It actually magnifies by about 2.2x.

 

I’ve checked it many times, it does not vignette a 13T6, or even many lower powered eyepieces.


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#23 YAOG

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Posted 09 December 2019 - 03:47 PM

The only reason I don't use the Celestron Ultima SV 2x anymore is the thumbscrew marks up eyepiece barrels, owning a TeleVue 2x Barlow, 2x 4x and 2.5x PowerMates, owning enough discreet eyepieces to not need it. Other than this it is an excellent Barlow for shorter f/l eyepieces. 


Edited by YAOG, 09 December 2019 - 04:39 PM.

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#24 SteveG

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Posted 09 December 2019 - 03:52 PM

The only reason I don't use the Celestron Ultima SV 2x anymore is the thumbscrew marks up eyepiece barrels, owning the 2x 4x and 2.5x PowerMates, owning enough discreet eyepieces to not need it. Other than this it is an excellent Barlow for shorter f/l eyepieces. 

I replaced my thumbscrew with a larger nylon lock screw.


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#25 Jon Isaacs

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Posted 09 December 2019 - 04:03 PM

I have a Japanese 2x Ultima Barlow that I purchased more than 20 years ago from Farah at Woodland Hills.  The difficulty with it, something they all shared, is the barrel was a very tight fit, the eyepiece would slide in but it was very slow.  

 

Playing with it right now, I see that it is simply an air compression issue, it's like a slip fit piston so the air has to flow between the barlow and the eyepiece barrel.

 

It is much easier with eyepieces with undercuts.  This must be the reason the vast majority of eyepieces today have undercuts, so they fit nicely into a 1998 Celestron Ultima Barlow.  :)

 

Jon


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