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Lens damage in my old Tele Vue 2.5mm Nagler T6 Eyepiece and successful eye lens replacement sourced from a 3.5mm Nagler T6

Eyepieces Optics Refractor Visual DIY
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#1 Castor

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Posted 06 December 2021 - 01:32 AM

Part 1: Damage in the eye lens of my 11-year old Tele Vue 2.5mm Nagler T6 Eyepiece.

 

Hi,

 

My core eyepiece set used with my refractors is a full set of Type-6 Nagler eyepieces plus a 24mm Panoptic, all purchased new between 11 and 15 years ago.  A few months ago I noticed that my 2.5mm Nagler T6 eyepiece had developed a problem in one of the lenses that manifests itself as a series of semi-transparent grooves all around the outer edge of the field of view (FOV) when looking through a telescope, encompassing about half of the viewing area.  The visual effect when looking at a bright object when it crosses the outer FOV is like looking through a layer of Vaseline spread over the lens!  Most of the time I use my telescopes in mild climates and take good care of my equipment (I don’t subject them to thermal shock) so I am at odds about the cause of this damage.

 

 

Here is a picture of my 2.5mm Nagler eyepiece hand held against a bright background looking at the eye lens, the rubber eye guard and showing part of the damage in the outer part of the FOV –due to the short eye relief most of the damage can’t be captured by the camera.  Two additional close-up pictures show the filamentary structure of the damage in the lens.

Attached Thumbnails

  • TeleVue-2.5mm-Nagler-T6-2010-damage-1200x720_105129.jpg
  • TeleVue-2.5mm-Nagler-T6-2010-damage-crop-800x800_104947.jpg
  • TeleVue-2.5mm-Nagler-T6-2010-damage-crop-800x800_110407.jpg

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#2 Castor

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Posted 06 December 2021 - 01:47 AM

Part 2: Direct lens replacement of my damaged 2.5mm Nagler Type-6 with the eye lens group from a 3.5mm Nagler Type-6 Eyepiece.

 

Since I own various refractors with a Focal Length (FL) ranging from 360mm to 660mm used on non-tracking Alt-Az mounts, I depend on my 2.5mm and 3.5mm Naglers for high magnification views, so losing either of them is not an option for me.  Unfortunately the 2.5mm Nagler T6 eyepiece was discontinued years ago and it doesn’t show up that often in the used market, the option that I’d prefer than shipping it to the manufacturer for repair.

 

As a general rule, I don’t disassemble an eyepiece for cleaning since I’d rather buy a replacement than risk causing irreversible damage due to inexperience or lack of the proper tools.  But once I declare an item as a total loss, as is the case with my 2.5mm Nagler eyepiece, I am no longer constricted by that rule.  So using a previous experience when I took apart my Meade Series 4000 6.7mm Ultra Wide Angle eyepiece for cleaning a couple of years ago, I went ahead and started disassembling the 2.5mm T6 Nagler with the intention to find the dirty lens and attempting to clean it if possible.

 

Unfortunately, I found that the damage of my 2.5mm Nagler was on the interior surfaces of the 2-element cemented eye lens and there was nothing that I could do to clean it –advanced ATMs with access to certain chemical substances can repair cemented lenses, but that’s beyond my abilities.

 

One important bit of information that I learned when I took the 2.5mm Nagler T6 eyepiece apart is that the eye lens group easily detaches by grabbing it from the eye guard and unscrewing it –no tools needed.  I compared it to my old 3.5mm Nagler T6 and I noticed that both unscrew at the same place.  Looking at the curvature of the lens by looking at reflections I started to wonder if they somehow shared the same lens design, after all: How many times have we read that short FL in the short FL Naglers is achieved by using a Smyth lens group at the front to produce high magnification?  So I did a thorough search on the astronomy forums trying to find out if someone had attempted to swap the lenses from T6 Nagler eyepieces, but my search came up empty.

 

Since swapping the 2.5mm Nagler 2-element eye lens group with the 3.5mm eye lens group is as easy as removing and replacing a screw bottle cap (it doesn’t require any tools, you only need to keep the eyepieces standing up to prevent the field lens group from accidentally coming out), I saw no harm in trying.  Fortunately, the bet paid off!  After screwing the 3.5mm eye lens group on the 2.5mm Nagler eyepiece, the eyepiece came back performing as good as it had for most of its lifespan.  I did a series of empirical tests with the eyepiece looking through a refractor on linear terrestrial structures and I couldn’t notice any aberrations or distortions after the eye lens swap.  I went back and forth multiple times testing both eye lens groups on the 2.5mm Nagler and the magnification remained the same on all the visual comparisons that I could make to the best of my ability.  Later at night, I tested the renewed 2.5mm Nagler on my TV-85 and NP127is refractors on DSOs and stellar objects and I didn’t notice any loss of performance of the eyepiece from my memory of its good old days.  So for all practical purposes, my 2.5mm Nagler T6 eyepiece is back to its normal used condition, as clean as you could expect from a well-used, well cared 11-year old eyepiece!

 

My intention with this posting is that next time someone is in the same situation that I was, when they do a search for a possible solution, hopefully they won’t come out empty handed!

 

Here is a picture of my old 2.5mm and 3.5mm Nagler T6 eyepieces with the eye lens group partially unscrewed.  Then a picture of my 2.5mm Nagler T6 eyepiece eye lens group detached showing the threads and rubber eye guard.  Last, a close-up picture showing the damaged, cemented 2-element lens, just for illustration, not necessary at all to extract it from its metal casing for doing the swapping.

Attached Thumbnails

  • TV-Nagler-T6-2.5mm+3.5mm-eye-lens-unscrewed-crop-800x800_101645.jpg
  • TV-2.5mm-Nagler-T6-2010-eyelens_group-removal-crop-480x800_123515.jpg
  • TV-2.5mm-Nagler-T6-2010-cemented_eyelens_group-crop-609x550_124854.jpg

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#3 Castor

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Posted 06 December 2021 - 01:52 AM

Part 3: Buying a brand new 3.5mm Nagler T6 Eyepiece to replace my old 3.5mm Nagler T6 eye lens group donor.

 

If the 2.5mm Nagler T6 eyepiece were still available for sale new, I would have purchased one and this thread would not exist.  But since there are no more new 2.5mm T6 Naglers, I used my 3.5mm Nagler T6 as a lens donor and went ahead and ordered a new 3.5mm Nagler T6 eyepiece to replace the old one.  Don’t get me wrong, for my modest budget buying a $335 eyepiece replacement is not an easy choice, but I find comfort in knowing that now my favorite, most frequently used eyepiece set along with the 24mm Panoptic is complete again! smile.gif

 

Here is a picture of my new 3.5mm Nagler T6 eyepiece just received two days ago and a picture of the three eyepieces together.

 

Attached Thumbnails

  • TeleVue-3.5mm-Nagler-T6-2021-1000x600_095310.jpg
  • TV-Nagler-T6-2.5mm+3.5mm+new-3.5mm-1000x600_101018.jpg

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#4 Ernest_SPB

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Posted 06 December 2021 - 02:32 AM

Great! It is a sample of effective approach to an issue...

But somewhat are still behind the scene...

(1) what was source of the damage

(2) did author an attempt to get some TV service


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#5 Jon Isaacs

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Posted 06 December 2021 - 02:44 AM

For what it's worth:

 

When I checked a few years ago, the lens group was $100 from TeleVue..

 

Jon


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#6 Scott in NC

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Posted 06 December 2021 - 03:23 AM

Nice save!  Thanks for sharing that info with us. waytogo.gif
 

Until reading this it never would have occurred to me that some of the TeleVue eyepieces have at least one element in common.  This is great to know for future reference!


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#7 Scott in NC

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Posted 06 December 2021 - 03:24 AM

For what it's worth:

 

When I checked a few years ago, the lens group was $100 from TeleVue..

 

Jon

I had no idea that TV could replace a few of the elements in a damaged eyepiece, but that’s good to know for future reference.


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#8 Redbetter

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Posted 06 December 2021 - 03:24 AM

For what it's worth:

 

When I checked a few years ago, the lens group was $100 from TeleVue..

 

Jon

I was going to suggest checking with TV.  It isn't a surprise that the top eyepiece lens group would be the same, or that they have parts.  I only wonder how many of the T6's share this same group...possibly all of them?


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#9 Castor

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Posted 06 December 2021 - 03:26 AM

Great! It is a sample of effective approach to an issue...

But somewhat are still behind the scene...

(1) what was source of the damage

(2) did author an attempt to get some TV service

(1) Unknown, as it was stated on my first post and as far as I can recollect, the eyepiece has not being mistreated: No rain, no freezing temperatures, no solar viewing, no strong vibrations, no outdoor storage, no dropping it, etc.

(2) No, that was not my first option.



#10 Castor

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Posted 06 December 2021 - 03:34 AM

Nice save!  Thanks for sharing that info with us. waytogo.gif
 

Until reading this it never would have occurred to me that some of the TeleVue eyepieces have at least one element in common.  This is great to know for future reference!

Thank you Scott! waytogo.gif

 

It was a wild guess that luckily turned out to be right but I have no idea if that’s the case with other T6 Naglers!


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#11 Castor

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Posted 06 December 2021 - 03:41 AM

For what it's worth:

 

When I checked a few years ago, the lens group was $100 from TeleVue..

 

Jon

Thank you Jon, that’s very useful information and it’s great that you posted it here for those considering their options! waytogo.gif 



#12 RAKing

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Posted 06 December 2021 - 05:31 PM

Wow!  First of all, I am sorry this happened to you and I hope someday you (or someone) will discover the source of the problem and explain it.

 

And that took guts to take a chance on damaging your 3.5 too, while trying to save the 2.5.  bow.gif

 

I hope your "new" 2.5 lives on for many more years of service!

 

Ron


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#13 Starman1

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Posted 06 December 2021 - 05:40 PM

It looks a little like the glue between two elements is failing, since it is from the outside in.

 

However, it also looks like a tool, like the one used to remove a retaining ring, slipped and made a circular scratch around the edge of the lens.

Except that would not have gone all the way around, so the delamination theory is probably true.

 

Someone else is reporting the same in an older Paracorr, and I think that some glue types might not withstand thermal shock over the years.


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#14 RichA

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Posted 06 December 2021 - 06:20 PM

For what it's worth:

 

When I checked a few years ago, the lens group was $100 from TeleVue..

 

Jon

Pricey.  I replaced the rear element of a Leica camera lens for about $60.00.  Their lenses run $2000+.



#15 turtle86

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Posted 06 December 2021 - 06:45 PM

Part 3: Buying a brand new 3.5mm Nagler T6 Eyepiece to replace my old 3.5mm Nagler T6 eye lens group donor.

 

If the 2.5mm Nagler T6 eyepiece were still available for sale new, I would have purchased one and this thread would not exist.  But since there are no more new 2.5mm T6 Naglers, I used my 3.5mm Nagler T6 as a lens donor and went ahead and ordered a new 3.5mm Nagler T6 eyepiece to replace the old one.  Don’t get me wrong, for my modest budget buying a $335 eyepiece replacement is not an easy choice, but I find comfort in knowing that now my favorite, most frequently used eyepiece set along with the 24mm Panoptic is complete again! smile.gif

 

Here is a picture of my new 3.5mm Nagler T6 eyepiece just received two days ago and a picture of the three eyepieces together.

 

Great work and glad this worked out for you.  I'm all thumbs myself and probably would've just sent it to Televue for service if possible.  Thanks for sharing this info.

 

I do wish I had picked up a 2.5 while they were still being sold.


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#16 Redbetter

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Posted 06 December 2021 - 07:55 PM

Pricey.  I replaced the rear element of a Leica camera lens for about $60.00.  Their lenses run $2000+.

So I interpret that as Leica is really sticking it to you in the price of a lens.  I suppose they have more parts and perhaps cheaper because they make more units, and do more repairs for camera lenses because of the nature of use.

 

Honestly, I am thrilled that there are companies like TV that have a stock of repair parts.  I consider $100 for ~1/3 of the lens assembly in $300+ eyepiece to be reasonable rather than "pricey."  Beats the heck out of replacement parts being simply unavailable at all.


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#17 Jon Isaacs

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Posted 06 December 2021 - 08:01 PM

So I interpret that as Leica is really sticking it to you in the price of a lens.  I suppose they have more parts and perhaps cheaper because they make more units, and do more repairs for camera lenses because of the nature of use.

 

Honestly, I am thrilled that there are companies like TV that have a stock of repair parts.  I consider $100 for ~1/3 of the lens assembly in $300+ eyepiece to be reasonable rather than "pricey."  Beats the heck out of replacement parts being simply unavailable at all.

 

I suspect $100 is, or at least was, their standard fee for a doublet lens.  I was also quoted $100 for the Smyth lens (field lens) for the 31 mm Nagler.

 

I think TeleVue is the only company that provides repair and parts for their lenses.

 

Jon

Jon


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#18 Castor

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Posted 07 December 2021 - 12:10 AM

Wow!  First of all, I am sorry this happened to you and I hope someday you (or someone) will discover the source of the problem and explain it.

 

And that took guts to take a chance on damaging your 3.5 too, while trying to save the 2.5.  bow.gif

 

I hope your "new" 2.5 lives on for many more years of service!

 

Ron

 

Hi Ron,

 

Thank you for your empathy and the good wishes! flowerred.gif 

 

I consider the 2.5mm Nagler essential for my small refractors and hopefully it will continue on duty for a few more years!

 

To be honest, the risk for my 3.5mm Nagler was minimal because removing the eye lens group only requires unscrewing the top part of the eyepiece located at the base of the rubber eye guard and swapping it with the one from the 2.5mm Nagler, no removal of a retaining ring was necessary for this, just keeping both eyepieces standing up on a flat surface while this is done.

 

Yes, I too hope someone will be able to discover the source of the problem and be able to explain it!  My first theory was possible failure of the cement that holds the two lens elements together (delamination), but given my lack of knowledge on this area I didn’t want to mention it until someone else brought it up, in this case it was Don, who is more than qualified to make an educated remark on the subject considering his ample knowledge and experience in the field.  In my years in the hobby I have seen a myriad of cases of mold/fungus growth on optics, never between cemented lens elements, but then I’m no mycologist so I can’t discard it as a probable cause for the damage.

 

Best,


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#19 Castor

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Posted 07 December 2021 - 12:16 AM

It looks a little like the glue between two elements is failing, since it is from the outside in.

 

However, it also looks like a tool, like the one used to remove a retaining ring, slipped and made a circular scratch around the edge of the lens.

Except that would not have gone all the way around, so the delamination theory is probably true.

 

Someone else is reporting the same in an older Paracorr, and I think that some glue types might not withstand thermal shock over the years.

 

Hi Don,

 

So good to count with your valuable input, thanks! smile.gif  I believe you are on the right track with you assessment about the cement failure because the damage in some places of the eye lens of the 2.5mm Nagler eyepiece manifests itself as concentric circles in the outer area of the FOV.  I’m still at odds about the ‘finger-like’ filamentary structure that occasionally points towards the center of the FOV.

 

Don, I can assure you that I didn’t make any scratches to the lens while disassembling it (I just confirmed it with a jeweler’s magnifying glass).  The straight and circular lines that you see in the picture are the ‘filaments’ shining with back illumination against the dark background.  Below is a crop picture showing a straight ‘scratch-like’ filament slightly out of focus.  Sorry for the poor quality!

 

Here are two pictures of just the eye lens group of the 2.5mm Nagler against a bright light showing the damaged area as a fuzzy ring encompassing the outer FOV -it reminds me of the Hubble images of the Helix Nebula.  The first picture is looking at the outer side of the eye lens (surrounded by the rubber eye guard) and the second picture is looking at the inner side of the eye lens (that goes on the internal side of the eyepiece).

Attached Thumbnails

  • TV-2.5mm-Nagler-T6-2011-eyelens-damage-exterior-crop-1050x1050_194353.jpg
  • TV-2.5mm-Nagler-T6-2011-eyelens-damage-interior-crop-1050x1050_194147.jpg
  • TeleVue-2.5mm-Nagler-T6-2010-eyelens-damage-filament-crop-600x600_105107.jpg


#20 Castor

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Posted 07 December 2021 - 12:21 AM

Great work and glad this worked out for you.  I'm all thumbs myself and probably would've just sent it to Televue for service if possible.  Thanks for sharing this info.

 

I do wish I had picked up a 2.5 while they were still being sold.

Thank you Rob, smile.gif  I was very lucky that my solution worked out for me!

 

Yes, sending the damaged eyepiece to Tele Vue for service is the most recommended course of action in these cases.

 

You may still get a chance to find a 2.5mm Nagler T6 in the classifieds if you are patient, I believe it’s worth it.  I don’t have a Paypal account so my options to buy used observing equipment are more limited than for most people here, otherwise I would have waited for one to show up.

 

Good luck! waytogo.gif 



#21 Starman1

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Posted 07 December 2021 - 10:39 AM

I didn't see the little radial lines at the very edge before.  That is definitely fungus and how it is attacking the glue in between the cemented lenses.

If it were on the outside of the lens, acetone would have removed it.

The reflections from spacers make the damage seem concentric.

I hope you cleaned the spacers and internal surfaces before reassembling.  I'd hate to think there was still fungus inside the eyepiece.


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#22 Castor

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Posted 07 December 2021 - 05:01 PM

Hi Don,

 

Thank you for your accurate diagnostic, I was afraid you were going to say it was fungus, frown.gif it makes perfect sense!

 

No, I didn’t clean the spacers or internal surfaces but now that I know I’ll do it ASAP, thanks! waytogo.gif  I’m glad that we now know the source of the problem. thanx.gif

 

Best regards,



#23 John Fitzgerald

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Posted 07 December 2021 - 05:17 PM

That lens could probably be taken apart with the correct solvent, and recemented.  Or, you could send the 3.5mm in for repair, and have a spare for much less than even a used one.


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#24 SteveG

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Posted 07 December 2021 - 07:36 PM

Hi Don,

 

Thank you for your accurate diagnostic, I was afraid you were going to say it was fungus, frown.gif it makes perfect sense!

 

No, I didn’t clean the spacers or internal surfaces but now that I know I’ll do it ASAP, thanks! waytogo.gif  I’m glad that we now know the source of the problem. thanx.gif

 

Best regards,

Did you ever check with TV to see what the replacement lens would cost?


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#25 Redbetter

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Posted 07 December 2021 - 08:16 PM

That lens could probably be taken apart with the correct solvent, and recemented.  Or, you could send the 3.5mm in for repair, and have a spare for much less than even a used one.

Doesn't need to be sent in since that would require a tech charge.  Instead just purchase the replacement part and self install.


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