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Best barlow for a Nagler 13T6

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#26 YAOG

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Posted 09 December 2019 - 04:36 PM

I'm sure that's why. LOL!


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#27 MitchAlsup

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Posted 09 December 2019 - 04:45 PM

Thanks for the help. I guess there's no escaping the exit pupil problem without ponying up for a Powermate. 

There are other telecentric focal length extenders.



#28 YAOG

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Posted 09 December 2019 - 04:52 PM

Does anyone know if there was more than one version of the Celestron Ultima SV 2x Barlow? I've owned several over the years/ decades and they were all exactly the same high quality.

 

Mine were all purchased used and marked Japan, were the popular shorty style with a chrome barrel, black metal body and red/orange markings, thumbscrew eyepiece retainer and gave me very good to excellent results when used with medium Plossl and ortho eyepieces. A handy size but maybe not as good as the longer TeleVue 2x with longer, wider AFOV eyepieces. The Ultima SV 2x can vignette and cause a loss of edge sharpness but it has been a while since I have used it for anything other than medium length 50 degree or less AFOV eyepieces.



#29 CollinofAlabama

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Posted 11 December 2019 - 02:02 AM

Adam, I had poor results with loss of color contrast with any eyepiece and the TeleVue 2x Barlow. See “Latest acquisition” in this forum for all the gory details, but I’ve had very, very good luck with the GSO 2.5x Barlow. It functions as a 2.1x magnifier, btw, but it’s marketed as the GSO 2.5x barlow. Excellent performance at a bargain price. Recommended!
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#30 CeleNoptic

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Posted 11 December 2019 - 02:26 AM


Does anyone know  if there was more than one version of the Celestron Ultima SV 2x Barlow? I've owned several over the years/ decades and they were all exactly the same high quality.

 

Mine were all purchased used and marked Japan, were the popular shorty style with a chrome barrel, black metal body and red/orange markings, thumbscrew eyepiece retainer and gave me very good to excellent results when used with medium Plossl and ortho eyepieces. A handy size but maybe not as good as the longer TeleVue 2x with longer, wider AFOV eyepieces. The Ultima SV 2x can vignette and cause a loss of edge sharpness but it has been a while since I have used it for anything other than medium length 50 degree or less AFOV eyepieces.

 

AFAIK, there were shorty #93506 (I had one) and long version of the Ultima SV, not sure, but seems like #93505. The shorty was vignetting e.g. a 14mm Meade 5K UWA, 20mm ES68, but overall worked nice with any shorter FL eyepieces except increasing spherical aberrations in UWA eyepieces, but all telenegative Barlows do that anyway. That why I prefer a Meade TeleXtender. 



#31 Adam Long

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Posted 12 December 2019 - 08:14 AM

There are other telecentric focal length extenders.

Any recommendations?

 

AFAIK, there were shorty #93506 (I had one)

Yeah that's the one I've got. Be interested to know which model SteveG is using.



#32 MrJones

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Posted 12 December 2019 - 12:33 PM

I've bought and sold quite a few Barlows at this point. I also didn't find the TV 2x Barlow to be very good and even a Parks and Japan Ultima were ultimately beat by these two for me:

 

My favorite shorty is the Baader 2.25. Q-Barlow. CN user Peter Besenbruch recommended the X-cel LX 2x Barlow a year or two in a discussion about this one. He complained about the Q-Barlow vignetting with longer FL EPs and it does. I do use it only for planetary and double stars. I was a little hesitant after I found the X-cel LX EPs mediocre but the X-cel 2x Barlow was cheap enough to try and I've found it an all around excellent performer. I use it often now and did try it with a 13T6 and I don't remember any issues other than I didn't keep the 13T6. I remember Peter saying he also use the X-cel 3x and I might try one as it's also cheap enough.


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#33 CeleNoptic

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Posted 12 December 2019 - 06:44 PM


Yeah that's the one I've got. Be interested to know which model SteveG is using.

 

Not sure but suspect he uses the same shorty Ultima which is more popular. The longer version is quite rear and I saw it only in classifieds maybe a couple of times. As I've said the shorty Ultima was vignetting my 14mm Meade UWA, but while it was noticeable I'd classified it as mild vignetting. I'm pretty sure SteveG doesn't see any vignetting in his 13mm NT6 because its FS is 17.6mm vs 18.9mm FS in the Meade.

 

 


I remember Peter saying he also use the X-cel 3x and I might try one as it's also cheap enough.

 

I can confirm the 3x X-Cel LX is an excellent Barlow, I was surprised when used it for the first time that so inexpensive Barlow can be that good. It's buffled pretty well, no scatter light, IMO. I think the 2x also made up to the same specs so you might notice that nice contrast when used your X-Cel LX.



#34 SteveG

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Posted 12 December 2019 - 07:32 PM

After reading these posts I decided to do a daytime test with my Ultima Shorty model 93506. In daylight, it's much easier to discern the field stop. I'm sad to report that the Ultima does indeed cause a small amount of vignetting frown.gif

 

I tested both the ES 24/68 and 20/68, and the N13T4. All three eyepieces showed a very tiny bit of vignette - about 2%. So I now stand corrected and sorry for the bad advice. I wasn't seeing it at night, but it's there. If I had to guess, the 68 deg eyepieces become 65 deg and the 82 become about 79 deg.

 

Now the question is; What shorty or lightweight 2x barlow does not vignette these eyepieces?

ES makes some nice focal extenders, but they are huge and heavy (I had the 3x).

 

I wonder if the newer E-Cel LX can do a better job? I've read nothing but great reports on this barlow. Seems like I'm going to have to try one now.


Edited by SteveG, 12 December 2019 - 07:33 PM.

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#35 SteveG

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Posted 12 December 2019 - 07:36 PM

I was a little hesitant after I found the X-cel LX EPs mediocre but the X-cel 2x Barlow was cheap enough to try and I've found it an all around excellent performer. I use it often now and did try it with a 13T6 and I don't remember any issues other than I didn't keep the 13T6. I remember Peter saying he also use the X-cel 3x and I might try one as it's also cheap enough.

If you still have the 2x X-Cel, can you report on its use with any of your longer focal length wide-fields?



#36 Starman1

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Posted 12 December 2019 - 07:45 PM

After reading these posts I decided to do a daytime test with my Ultima Shorty model 93506. In daylight, it's much easier to discern the field stop. I'm sad to report that the Ultima does indeed cause a small amount of vignetting frown.gif

 

I tested both the ES 24/68 and 20/68, and the N13T4. All three eyepieces showed a very tiny bit of vignette - about 2%. So I now stand corrected and sorry for the bad advice. I wasn't seeing it at night, but it's there. If I had to guess, the 68 deg eyepieces become 65 deg and the 82 become about 79 deg.

 

Now the question is; What shorty or lightweight 2x barlow does not vignette these eyepieces?

ES makes some nice focal extenders, but they are huge and heavy (I had the 3x).

 

I wonder if the newer E-Cel LX can do a better job? I've read nothing but great reports on this barlow. Seems like I'm going to have to try one now.

Baader VIP.



#37 SteveG

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Posted 12 December 2019 - 07:50 PM

Baader VIP.

For $270 I hope so. My barlow is only used with my $200 travel scope. I could buy a used N7T6 for that kind of money, and forget the barlow.



#38 MrJones

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Posted 13 December 2019 - 10:23 AM

If you still have the 2x X-Cel, can you report on its use with any of your longer focal length wide-fields?

Oh I still have it, it's a keeper for me. With daylight tests my BCO 18mm and ES68 24mm both have the outer 1-2% vignetted. So not much but enough to see in the day. It's very slightly more with the Q-Barlow, maybe 2-3%. The ES68 24mm was very slightly more vignetted than the BCO 18mm in both and is strange in the Q-Barlow, the eye relief actually seems less. My 15x Nikon microscope EP (about 16mm FL with 30mm barrel) showed no vignetting in either.


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#39 SteveG

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Posted 13 December 2019 - 02:48 PM

Oh I still have it, it's a keeper for me. With daylight tests my BCO 18mm and ES68 24mm both have the outer 1-2% vignetted. So not much but enough to see in the day. It's very slightly more with the Q-Barlow, maybe 2-3%. The ES68 24mm was very slightly more vignetted than the BCO 18mm in both and is strange in the Q-Barlow, the eye relief actually seems less. My 15x Nikon microscope EP (about 16mm FL with 30mm barrel) showed no vignetting in either.

OKay, thanks for checking. Seems like the Powermate/focal extender is the way to go if you don’t want vignetting. I might have to try the ES 2x telecentric.

 

This is one of those “now that I see it, I can’t unsee it” moments!


Edited by SteveG, 13 December 2019 - 02:51 PM.

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#40 JimV

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Posted 13 December 2019 - 11:21 PM

I would use a 1.25" to 2" adapter with a 2" barlow.

That will solve the vignetting problem.  Any quality 2" barlow will work well.



#41 YAOG

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Posted 14 December 2019 - 01:11 PM

Oh I still have it, it's a keeper for me. With daylight tests my BCO 18mm and ES68 24mm both have the outer 1-2% vignetted. So not much but enough to see in the day. It's very slightly more with the Q-Barlow, maybe 2-3%. The ES68 24mm was very slightly more vignetted than the BCO 18mm in both and is strange in the Q-Barlow, the eye relief actually seems less. My 15x Nikon microscope EP (about 16mm FL with 30mm barrel) showed no vignetting in either.

If you can see the vignette it is a lot worse than you think. IMO the best solution is a 2" PowerMate for wider and/or longer focal length eyepieces. One of the great things about the 2" PowerMates is they can be used for imaging too. On the C11 when used with the 4x PowerMate and a ASI174 you can capture amazing planetary images. 

 

But Barlow's still have a place IMO, they work very well as minimal glass options for short narrower 50 AFOV and less eyepieces, think planetary or small DSOs needing some power kind of use and where the user doesn't want to invest a billion US dollars to have a high-end eyepiece for every possible occasion like some of the crazy people here.



#42 SteveG

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Posted 14 December 2019 - 03:30 PM

I would use a 1.25" to 2" adapter with a 2" barlow.

That will solve the vignetting problem.  Any quality 2" barlow will work well.

The OP wants to keep it at 1.25”.  
 

In my case, it must be 1.25”.



#43 YAOG

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Posted 14 December 2019 - 04:38 PM

The OP wants to keep it at 1.25”.  
 

In my case, it must be 1.25”.

Where did the OP post that it has to be 1.25"?



#44 SteveG

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Posted 15 December 2019 - 03:46 PM

Where did the OP post that it has to be 1.25"?

Sworry. The discussion has only been about 1.25” barlows. It’s been going for a while now so I thought we were limited to that.



#45 BDS316

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Posted 18 December 2019 - 07:10 PM

I replaced my thumbscrew with a larger nylon lock screw.


I'd love to get a nylon lock screw for my Televue 1.8x Barlow...any idea where I could get one? Thanks.

#46 Starman1

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Posted 18 December 2019 - 08:46 PM

Local hardware store or McMaster-Carr on line.


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#47 Adam Long

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Posted 19 December 2019 - 05:53 AM

Sworry. The discussion has only been about 1.25” barlows. It’s been going for a while now so I thought we were limited to that.

The impetus was really just to find if there is a cheaper way of getting a nice widefield 6-7mm eyepiece than simply buying one.

 

I'll no doubt buy one eventually but for now the Celestron SV and 13T6 is working pretty well, and the barlow has other uses too, so a decent addition to my kit for £40. A quick search suggest I could pick up a used GSO 2" 2x barlow for a similar amount, so that might be an idea but I'm not sure what else I'd use that for so maybe better to put that cash into future eyepiece?

 

I'd estimate the AFOV with the 13T6 and SV combo to be ~65 degrees. I find it looks worse through a scope in the dark than just peering through in the daylight - I can see the field stop like that but not when in use. But it is sharp across that field and perfectly usable

 

Playing around with the SV barlow and other eyepieces seems to show little correlation between vignetting and focal length and afov. Getting a little out of my depth here, but assuming this is determined by the position of the eyepiece entry pupil? The focus position of the 13T6 (on it's own) is the furthest out of all my eyepieces.



#48 25585

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Posted 19 December 2019 - 07:30 AM

OKay, thanks for checking. Seems like the Powermate/focal extender is the way to go if you don’t want vignetting. I might have to try the ES 2x telecentric.

 

This is one of those “now that I see it, I can’t unsee it” moments!

I use the ES 2" 2× version, and its very pleasing. 

 

Generally any 2" will avoid vignetting a 1.25". So a GSO 2" 2× would be an inexpensive alternative.



#49 vahe

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Posted 19 December 2019 - 10:12 AM

I wonder how wise it is to use a Barlow with an eyepiece that has a built in Barlow, I suppose two Barlows is better than one and three Barlows would be even better that two in the light path.

.

Vahe



#50 SteveG

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Posted 19 December 2019 - 02:56 PM

I'd love to get a nylon lock screw for my Televue 1.8x Barlow...any idea where I could get one? Thanks.

Scopestuff sells a variety pack that will have one that fits your threads. In my case, a bought a larger 1/4-20 nylon thumbscrew, and drilled and tapped the larger threads in the barlow. It will hold anything in place now.




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