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Holy Pincushion Batman! Nagler 26

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#1 HellsKitchen

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Posted 15 April 2021 - 02:26 AM

So last night, with the southern Milky Way well overhead, I finally decided to give my Nagler 26T5 a try in my 130mm F/5 reflector. The wide field is very nice, and the Milky Way fields sparkle, but I was surprised by what I found out was pincushion distortion. Sweeping through the Milky Way, it was like wooahhh shouldn't have drank that bottle of Wild Turkey 101!  All you hear is how great TV eyepieces/Naglers are so I was taken aback, did not expect to see this. Stars near the edge fanned out, so not 'perfection' near the edge, but that was the coma from the F/5 system, and I assume coma is more evident in an ultra wide EP than an equivalent narrower field. Is my assumption correct?

 

The Nagler, and 82* EPs in general, is a brand new experience to me, so I am not at all familiar with its nuances. After doing a bit of reading, it appears that what I saw is infact a part and parcel of the Nagler, and other ultra wides. I guess the shock comes from the fact that on a regular basis I've only used LVWs, Delites, and plossls and never actually dabbled with uwa eyepieces. 

 

Other scopes I'll try in are a 72mm F/6 refractor and a 8" F/6 dob, might clear up tonight hopefully. Trying in the 12" will have to wait as that's a much bigger setup and only worth the effort at my dark site, which atm I am too busy with work to head out to (home has too many trees and crud in the way).

 

For coma I have a paracorr 2 as my 12" is F/4.38, what is the correct setting for the 26 Nagler from your experiences? Televue's leaflet says the "F" position, would that be it? And does one focus the scope before adjusting the paracorr, or vice versa?

 

I used to live the simple life...


Edited by HellsKitchen, 15 April 2021 - 05:12 AM.


#2 areyoukiddingme

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Posted 15 April 2021 - 02:34 AM

I haven't tried the 26, but the 31 certainly has a good bit of pincushion distortion.

 

At F5, there's plenty of coma to be seen. The paracorr will clean that up so it'll be pinpoint stars all the way across.

 

The pincushion will remain, but you may find you get used to it. I took a good while to sell my ES 30/82, because it has less pinchusion than the 31 Nagler, and at this kind of focal length, panning around is a common use.

 

But the Nagler won out with better edges, and more saturated star colors. I've since become used to the pincushion, and it doesn't bother me as much as it did.

 

As for settings, just follow the TV advice on the Paracorr setting, then focus the scope. If you have an eyepiece you do not know the correct paracorr setting for, just swap out the 26 Nagler after it is set and focused. Use the coma corrector adjustable top to find focus, and you will be at the optimal setting.


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#3 Kunama

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Posted 15 April 2021 - 05:22 AM

I always used the N26 with the SIPS so am unfamiliar with its performance without a coma corrector.... with the SIPS is was excellent even in my F3.5 18".


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#4 RedzoneMN

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Posted 15 April 2021 - 05:33 AM

It is a fantastic low power eyepiece in my 24 f3.3 with SIPS. Nicer form factor than the 31N/21E.  It’s a shame that they stopped making it. 


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#5 Sarkikos

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Posted 15 April 2021 - 06:16 AM

You really can't give an accurate appraisal of the optical performance of an eyepiece in an Newt at f/5 or less without a coma corrector in the system.

 

Mike


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#6 HellsKitchen

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Posted 15 April 2021 - 06:31 AM

You really can't give an accurate appraisal of the optical performance of an eyepiece in an Newt at f/5 or less without a coma corrector in the system.

 

Mike

 

This isn't meant to be an accurate appraisal or review, just an observation that was surprising to me, clearly because I've come from using a completely different class of eyepieces in my time in this hobby and my lack of real world experience with Naglers.

 

My main purpose for the ep is to use it with my 12", and yes with a CC. 

 

@areyoukiddingme - thankyou, answers a few questions for this Nagler noob waytogo.gif


Edited by HellsKitchen, 15 April 2021 - 06:43 AM.


#7 Sarkikos

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Posted 15 April 2021 - 07:03 AM

When wide field eyepieces are designed, the designers have a choice between RD (rectilinear distortion) and AMD (angular magnification distortion), or some compromise between the two.   AMD will enlarge objects - such as stars - in the outer field.  RD can be pincushion or barrel.  For astronomical eyepieces, they usually avoid AMD and opt for RD.  If coma is in the system, it can make optical problems toward the edge of field seem even worse.

 

Unless I'm looking for it, I hardly notice RD in eyepieces.  Many amateur astronomers just get used to it.  What many of us do notice is a fuzzy outer field due to AMD, astigmatism, FC (field curvature) and/or coma.  Coma makes every outer field problem look worse.

 

Mike


Edited by Sarkikos, 15 April 2021 - 07:09 AM.

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#8 HellsKitchen

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Posted 15 April 2021 - 07:24 AM

Thanks Mike, that's a very good clear explanation. waytogo.gif Looking forward to trying the EP in my frac and eventually the 12" once work settles down. Like with anything new, I'm sure I'll get used to it once I "wear it in". I'm already liking the wide fov, and Eta Carina looked very nice. Glittering is the word I'd use. New territory for me after spending most of the hobby above 200x with 60*-odd eyepieces.


Edited by HellsKitchen, 15 April 2021 - 07:24 AM.

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#9 SeattleScott

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Posted 15 April 2021 - 11:49 AM

TV eyepieces are especially known for pincushion. There is no such thing as a perfect UWA so you kind of have to pick your poison, and TV errors on the side of pincushion.

I went with the ES 24 82 instead since it was about half the price at the time, and it does a very nice job, sharp stars across the field with CC at F4. It has a 34mm field stop instead of 35 for the 26 Nagler. So about 3% smaller view but could be an option if the pincushion bothers you. Never compared it to a 26 Nagler. I have used the 31 and the pincushion didn’t seem to bother me.

Presumably the 26T5 is a little sharper than the ES so first option would be to see if you get used to the pincushion. But if it continues to bother you, it could make perfect sense to get a different eyepiece that agrees with you more, especially considering you could easily sell the 26 for more than the 24 would cost you. Certainly some have sold a 24 Panoptic to get a 24 APM, 24 ES, or 22LVW. That 26mm cost you a chunk of change. If it doesn’t agree with you, find something that does. That being said, sometimes it does take a few sessions to warm up to an eyepiece.

Scott
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#10 Starman1

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Posted 15 April 2021 - 05:34 PM

So last night, with the southern Milky Way well overhead, I finally decided to give my Nagler 26T5 a try in my 130mm F/5 reflector. The wide field is very nice, and the Milky Way fields sparkle, but I was surprised by what I found out was pincushion distortion. Sweeping through the Milky Way, it was like wooahhh shouldn't have drank that bottle of Wild Turkey 101!  All you hear is how great TV eyepieces/Naglers are so I was taken aback, did not expect to see this. Stars near the edge fanned out, so not 'perfection' near the edge, but that was the coma from the F/5 system, and I assume coma is more evident in an ultra wide EP than an equivalent narrower field. Is my assumption correct?

 

YES, THE WIDER THE APPARENT FIELD, THE MORE VISIBLE COMA IS.

 

The Nagler, and 82* EPs in general, is a brand new experience to me, so I am not at all familiar with its nuances. After doing a bit of reading, it appears that what I saw is infact a part and parcel of the Nagler, and other ultra wides. I guess the shock comes from the fact that on a regular basis I've only used LVWs, Delites, and plossls and never actually dabbled with uwa eyepieces. 

 

DUE TO THE NATURE OF OPTICS, DISTORTION INCREASES WITH FIELD WIDTH.  SCANNING ACROSS THE SKY WITH AN ULTRAWIDE WILL ALWAYS SHOW SOME FORM OF DISTORTION, AND PINCUSHION IS BETTER THAN ANGULAR MAGNIFICATION DISTORTION (YOUR OTHER POSSIBILITY).  IT ISN'T AN ISSUE ONCE YOU FIND A FIELD AND STOP THERE.  IF DISTORTION BOTHERS YOU, STICK TO NARROWER FIELDS OF VIEW.

 

Other scopes I'll try in are a 72mm F/6 refractor and a 8" F/6 dob, might clear up tonight hopefully. Trying in the 12" will have to wait as that's a much bigger setup and only worth the effort at my dark site, which atm I am too busy with work to head out to (home has too many trees and crud in the way).

 

For coma I have a paracorr 2 as my 12" is F/4.38, what is the correct setting for the 26 Nagler from your experiences? Televue's leaflet says the "F" position, would that be it? And does one focus the scope before adjusting the paracorr, or vice versa?

 

YES, TELEVUE IS RIGHT ON THE POSITION OF THE PARACORR.  YOU DIAL THE LETTER, INSERT THE EYEPIECE, THEN FOCUS THE SCOPE.  TO FIND THE PARACORR POSITION FOR ANY OTHER EYEPIECE, REMOVE THE 26, INSERT THE OTHER EYEPIECE AND FOCUS USING THE TUNABLE TOP OF THE PARACORR.  WHATEVER SETTING RESULTS IS THE SETTING FOR THAT EYEPIECE.  iN THAT WAY, YOU CAN FIND THE IDEAL POSITION FOR EVERY EYEPIECE IN YOUR SET.

 

I used to live the simple life...


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#11 Jeff Morgan

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Posted 15 April 2021 - 10:21 PM

It is a fantastic low power eyepiece in my 24 f3.3 with SIPS. Nicer form factor than the 31N/21E.  It’s a shame that they stopped making it. 

 

After nearly 30 years with a 22 Panoptic, I replaced it with a 26 Nagler last fall - and really love the eyepiece. Optical character of the 31N without the weight of a 22N. A perfect fit to my collection too.

 

Pincushion? What pincushion? (What else would you expect a long-time Panoptic owner to say?)

 

The real answer for the OP is to get a mount with a drive. Everything gets better when the earth stands still.



#12 Jon Isaacs

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Posted 15 April 2021 - 10:43 PM

After nearly 30 years with a 22 Panoptic, I replaced it with a 26 Nagler last fall - and really love the eyepiece. Optical character of the 31N without the weight of a 22N. A perfect fit to my collection too.

 

Pincushion? What pincushion? (What else would you expect a long-time Panoptic owner to say?)

 

The real answer for the OP is to get a mount with a drive. Everything gets better when the earth stands still.

 

A driven mount has value but when it comes to pincushion, it's really only apparent when scanning the sky.  If the scope is just left to drift, the process is very slow, in a 12 inch F/5 like the OP's, it has a 1.3 degree TFOV and it will take at least 5 minutes to drift across the field.  

 

If you are scanning, whether it's by hand or with the mount, the effect of the pincushion will be about the same.  

 

Personally, it doesn't bother me.

 

Jon


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#13 SeattleScott

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Posted 16 April 2021 - 12:45 AM

Agreed, pincushion is a panning issue not a tracking issue. Getting a goto scope could solve the problem, but not just a motor drive.

Scott

#14 HellsKitchen

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Posted 16 April 2021 - 06:30 AM

Alright, so tonight I tried the 26 Nagler in my 72mm f/6 WO refractor. It's safe to say that I am now sold. Beautiful, beautiful widefields of the Milky Way. Eta Carina was exquisite. The carbon star next to Beta Crucis clearly showed its colour. Almost the entire LMC fits in the field, and with a  UHC, covered in knots. Stars really are crisp essentially right to the edge, only the FC from the refractor means a tiny bit of refocusing required from the centre to the edge. Somehow the pincushion was less pronounced, perhaps I'm already getting conditioned or the removal of coma lessened the effect. The 82* field is very nice, feels natural. 

 

Using the refractor tonight also made it clear how much coma is in an F/5 newtonian, it just was never as apparent before because I was using narrower field eyepieces. I think I just mistakenly blamed some of it as pincushion in the eyepiece. Simply trying a different scope can answer many questions.

 

The paracorr will definitely be mandatory on my 12". Thanks for the help guys, and Don, areyoukiddinme, for the paracorr tutorial. waytogo.gif


Edited by HellsKitchen, 16 April 2021 - 06:30 AM.

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#15 SandyHouTex

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Posted 16 April 2021 - 09:07 AM

So last night, with the southern Milky Way well overhead, I finally decided to give my Nagler 26T5 a try in my 130mm F/5 reflector. The wide field is very nice, and the Milky Way fields sparkle, but I was surprised by what I found out was pincushion distortion. Sweeping through the Milky Way, it was like wooahhh shouldn't have drank that bottle of Wild Turkey 101!  All you hear is how great TV eyepieces/Naglers are so I was taken aback, did not expect to see this. Stars near the edge fanned out, so not 'perfection' near the edge, but that was the coma from the F/5 system, and I assume coma is more evident in an ultra wide EP than an equivalent narrower field. Is my assumption correct?

 

The Nagler, and 82* EPs in general, is a brand new experience to me, so I am not at all familiar with its nuances. After doing a bit of reading, it appears that what I saw is infact a part and parcel of the Nagler, and other ultra wides. I guess the shock comes from the fact that on a regular basis I've only used LVWs, Delites, and plossls and never actually dabbled with uwa eyepieces. 

 

Other scopes I'll try in are a 72mm F/6 refractor and a 8" F/6 dob, might clear up tonight hopefully. Trying in the 12" will have to wait as that's a much bigger setup and only worth the effort at my dark site, which atm I am too busy with work to head out to (home has too many trees and crud in the way).

 

For coma I have a paracorr 2 as my 12" is F/4.38, what is the correct setting for the 26 Nagler from your experiences? Televue's leaflet says the "F" position, would that be it? And does one focus the scope before adjusting the paracorr, or vice versa?

 

I used to live the simple life...

Don’t use any Panoptics then.  They’re even worse.  You’llfeel like you drank an entire case of Wild Turkey.


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#16 hoof

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Posted 16 April 2021 - 11:52 PM

Yup.  Pincushion is why I sold my 24mm Panoptic shortly after buying it way back when.  It's also why when my 30mm Meade 5k UWA succumbed to fungus, it was replaced with an ES 30mm UWA (which has the same optics), despite my financial situation easily allowing for the 31mm T5 Nagler.  

 

The T5 Naglers are a scaled design, so their distortion characteristics should be identical for all of them.

 

I bought my 24mm Panoptic to turn my 4.5" Starblast into a rich field telescope.  It did that really well, until I started sweeping around.  I literally felt nauseous.  The 22mm Vixen LVW (Orion labelled) that replace it had none of the issues, and I still own it 15 years later.

 

For a low power eyepieces, pincushion is intolerable to me as I use those to sweep around looking at stuff.  

 

Don't get me wrong, I'm not anti-Televue.  I own eight TV eyepieces, three Paracorrs, including five Ethos (21mm, 2x13mm, 8mm, 6mm).  I just find the choice of distortion in TV Panoptics and T5 Naglers to be disagreeable with me for what I use those powers for.


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#17 HellsKitchen

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Posted 19 April 2021 - 07:05 AM

I've never had Panoptics on my radar as I had a full set of LVWs. I sold most of them to make way for Delites, but the LVWs are fantastic eyepieces and are basically aberration free. However, their coatings are outdated and are heavy for what they are. I pitted my 5mm LVW against my 5mm Delite, and the Delite provided what was to me clearly more transmission and was sharper, clearer, more intense. I now have 3,4,5,7,9 mm Delites and they are essentially flawless. Viewing the moon in good seeing at high power in a Delite is something that bends the boundaries of reality.  I am considering the 11 and 15mm aswell to fill the gap to my 22mm LVW in my 1.25" set. 

 

Another session with my 72mm WO Megrez, and the 26 Nagler is really growing on me, and the 82* field is very nice. I am half considering getting more Naglers, or even trying the Ethos range. I am really considering hard to get a 120ST.  Infact, my dark site is in a grey zone/ Bortle 2, is only a 20km drive, a black site/ Bortle 1 is only another 10 mins up the road, it would be a crime to not get an ST120.

 

Nah, the coma in my F/5 newt at that 82* field was what was really bothering me, rather than the pincushion in the Nagler. I can now see that. 


Edited by HellsKitchen, 19 April 2021 - 07:54 AM.

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