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Objective Clam Chip -- can I glue?

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#1 FredSoDak

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Posted 27 September 2021 - 08:10 PM

Just purchased a used 102AZ f=660 refractor. Objective has a chip.  Looking for inexpensive options; just leave it alone, blacken it, glue it, replace it?  The chip is on the non-convex lens.  I have not had the opportunity to view at night; however, daytime viewing around the yard seemed OK.  This was a low cost purchase and I would like to keep it that way; if glueing is an option, what type of glue is preferred?  The lens cell housing is plastic.  Lens edges are not blackened.

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#2 Jim Waters

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Posted 27 September 2021 - 08:13 PM

"can I glueNO

 

If you can, return it.


Edited by Jim Waters, 27 September 2021 - 08:16 PM.


#3 markb

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Posted 27 September 2021 - 08:54 PM

Return it.

 

Gluing simply won't / can't eliminate the issue.

 

If that is not possible the malady is nearly cured by 1) carefully grinding the chip to a matte finish with a carborundum stone and then 2) finishing it with Higgins Black Magic India Ink (Amazon, pen style is easiest) or a flat black Tamiya model paint.

 

Surprisingly little or no perceptible image degradation after matteing and blackening. The chips otherwise reflect internally.

 

Avoid sharpies, they don't come close to the same effect.

 

I've done this several times, refining it to this method.

 

If you get the Higgins pen, edge blackening is a piece of cake, just get a vertical support to hold the lens as you work. Moderately alcohol soluble so work clean to avoid later solvent issues in cleaning before reassembly.

 

Old Jaegers refractors were famous for flint glass chips (sob) and I've used this method for classic clam shells and a crazy overtightened induced series of edge flakes.

 

I've used the Higgens for edges too, and for binocular ground prism edges as well. Awesome.

 

I've had weird breakdown and high reflectivity issues with sharpie, not recommended.


Edited by markb, 27 September 2021 - 08:56 PM.

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#4 Mitrovarr

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Posted 28 September 2021 - 12:38 AM

Just blacken it. You can't repair it, any attempt with glue will be worse than nothing. You can't truly fix it and the closer it gets to behaving like the rest if the lens, the more damage it will do to the image.

Once blackened it will behave like a little tiny obstruction which will only have a very minor effect.
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#5 teashea

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Posted 28 September 2021 - 07:39 PM

Just purchased a used 102AZ f=660 refractor. Objective has a chip.  Looking for inexpensive options; just leave it alone, blacken it, glue it, replace it?  The chip is on the non-convex lens.  I have not had the opportunity to view at night; however, daytime viewing around the yard seemed OK.  This was a low cost purchase and I would like to keep it that way; if glueing is an option, what type of glue is preferred?  The lens cell housing is plastic.  Lens edges are not blackened.

No


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#6 FredSoDak

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Posted 28 September 2021 - 08:22 PM

Thank you all for the advice. 

 

In the process of ordering replacement objective lens.  Cannot find any 660mm focal length, so may have to go with 600mm.  The OTA tube itself, I believe, is actually constructed for a 600mm; because it has a focuser with an extra long tube (as compared to my 2 other refractor focusers).  When I do view in the daytime, I must use an extension (old barlow housing) with the other focusers, as well as having the tubes almost maxxed outward; but no extension is required with the focuser that came with the scope.

 

Cannot view at night, due to light scattering/dispersion.  Daytime views are great (much better than ST120 f/5 -- even when stopped down to 90mm) -- all I have done for now is to place black electrical tape over that portion where the chip is located.



#7 markb

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Posted 28 September 2021 - 08:33 PM

At least use a stone to grind the chip matte. It really knocks down internal reflections.


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#8 CHASLX200

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Posted 29 September 2021 - 05:58 AM

No glue magoo. I say send it back if you can.



#9 FredSoDak

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Posted 29 September 2021 - 08:58 AM

At least use a stone to grind the chip matte. It really knocks down internal reflections.

I moved the black electrical tape from the front of the objective (on the convex lens) to the side that has the actual clam chip (the non convex lens with side facing the focuser).  It cut down internal reflections -- drastically.  Jupiter had no scattering.  A street light 400 feet away came into perfect focus.

Did a side by side comparison with the ST120 f/5 masked to 90mm last night.  Almost identical with new tape placement.


I like your idea of grinding.  Do you hand grind, or put on a dremel?  Is wet grinding preferred?

Also, what is the approximate drying time for the Higgins pen ink; as not having used it.

I also appreciate the people who have stated to return it; but the complete expense of the used kit was less than $100.  The mount is already being used for another OTA (as was the intention).  A replacement lens doublet achromat (600mm focal length) for this is priced at $85-$105 (unexpected expenditure).



#10 Mike Spooner

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Posted 29 September 2021 - 10:51 AM

Try it on a bright star and see if there is a flare - I have a 20mm Nagler that was apparently dropped on concrete and damaged the field lens. I paid an appropriate price for the eyepiece but to be honest I have never seen anything bothersome in the image. I’ve had a few scopes with clam chips and visually they seemed fine. Photographically they most likely will impact bright stars. Just ‘cause I like messing with stuff, I would try a very tiny bit of superglue (with a bit of pressure) and do a before and after check - you could always blacken the area later if desired. Just be careful not to smear the glue on the good part. But that risk is a personal choice and the optician side of me is pretty reckless compared to my early years.lol.gif 
 

But if you’re not seeing any effects, might be prudent to just enjoy it as is. 

 

Mike Spooner 



#11 FredSoDak

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Posted 29 September 2021 - 12:38 PM

Just ‘cause I like messing with stuff, I would try a very tiny bit of superglue (with a bit of pressure) and do a before and after check - you could always blacken the area later if desired. Just be careful not to smear the glue on the good part. But that risk is a personal choice and the optician side of me is pretty reckless compared to my early years.lol.gif 
 

Mike Spooner 

I thought of that also, -- but I don't know the meaning of "a very tiny bit" -- one drop immediately becomes 3 or more and finally, where's the acetone.



#12 markb

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Posted 29 September 2021 - 02:22 PM

I hand grind with a regular small carborundum stone. I guess a Dremel would work, but one 'catch' and you get a ground squiggle across the lens.

 

Watch your pressure, don't make new chips.

 

Round tip stones exist too I think.

 

I might have used Emory cloth too, not sure.

 

That kills most of the internal multiple mirroring effect but still needs to be blackened.

 

Higgins dries in minutes, even the Tamiya paints are reasonably fast. Just remember the Higgins can dissolve in alcohol, handy for mistakes.


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#13 FredSoDak

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Posted 29 September 2021 - 02:40 PM


I might have used Emory cloth too, not sure.

 

That kills most of the internal multiple mirroring effect but still needs to be blackened.

 

Higgins dries in minutes, even the Tamiya paints are reasonably fast. Just remember the Higgins can dissolve in alcohol, handy for mistakes.

Thank you.

I have plenty of emory cloth around -- will try it first.

We have badly needed scattered rain forecast for the next few days.




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