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Fo_Cuss

Has anyone unglued and reglued an eyepiece doublet?

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Has anyone unglued and reglued an eyepiece doublet?

In order to solve some problems that I was having, with a Celestron 4mm Omni Plossl, the eyepiece was dismantled.

The scope-side doublet was found to have been misaligned during assembly :

image.jpeg.3c2d4e13da0815b092b423b841bc6bdd.jpeg


I'm guessing that the lenses are superglued together.

The method that I'm considering, would be to place the lens, flat(ish) side down, on wood, in a pre-cut delve, probably adding panel pinning for stability
... and place in the oven.
Over-cook the lenses, in order that they stay above the bond temperature...
Using plastic pincers, and a piece of card ... clamp to wood, and apply the micrometer anvils (or vice versa - probably less risky).

Then leave it ... hoping that the bond remakes.

I'd be loath to apply liquid superglue, because it is likely to wick through the gap.
I need 'gel superglue', to reinforce what I would hope would be auto rebonded lenses.

It sounds simple enough, but it's a task that can easily go wrong, and end up with superglue being smeared across the lens faces.
This is why I'm thinking that panel pins would be a good idea.

Another Risk might be glue vapour.
Over-cook yes ... but not enough to vaporise the glue.

Anyway, that's one current planning option.

Perhaps another method would be to melt the glue in boiling water (if it will melt), and then clean off the lenses with acetone.
... before cold gluing.

The other option is to leave the task for the moment, and re-benchmark the eyepiece after completing the various required mods.
... but, it's out, it needs doing, and after a few practice runs, the actual task might be done in under 30 seconds.

Either way, the task needs reviewing.

If anyone has any prior experience in this area ... I'm all ears  🌝


 

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I think the glue used to cement lens elements is of the type that hardens when exposed to ultraviolet light. That allows for time to position the elements before fixing them.

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3 minutes ago, Ruud said:

I think the glue used to cement lens elements is of the type that hardens when exposed to ultraviolet light. That allows for time to position the elements before fixing them.

Thanks Ruud.
That is the sort of insight that I'm looking for.

I guess that I need to tap that into a search box :)

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Not too expensive :
https://www.ebay.co.uk/itm/10ML-CRYSTAL-REPAIR-UV-RESIN-GLUE-FOR-GLASS-METAL-FURNITURE-9-LED-UV-TORCH-/251849837936?

Or there is a pen type for £5.50 with a UV lamp in the pen.

Here is what Permabond have to say about de-bonding :

UV Cure Adhesives: Extra care needs to be taken as substrates are typically glass and cannot be peeled, whacked or levered of course! The heating method of adhesive de-bonding could be a problem if the substrate materials are glass to metal as differential thermal expansion and contraction could cause glass cracking. However, glass to glass you could heat to the point the adhesive degrades permanently (>200°C). Glass to metal can be soaked in solvent as per other adhesive types.  Plastics which have been bonded with UV adhesive such as polycarbonate or acrylic will be attacked by solvent. Even if you manage to get the components apart, removing cured adhesive will be a problem.  Check the water absorption rates with the manufacturer; some products will absorb water.  Boiling the parts in water may allow the adhesive to absorb enough water to soften it.  Complete the removal while the adhesive is still wet as upon drying the strength will return.

So it's messy.

Cooking will do it, but the glue is permanently destroyed, and would then need removing.
Acetone would presumably work, but the disolved glue would go everywhere ... though ultimately would entirely dissolve, allowing a fresh acetone rinse.
Boiling water would work, but that would leave a mess of soft glue that will reharden.

Out of the three options, it looks like acetone will be the best route.

Thanks again Ruud for that mission critical information  🌝

 

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15 minutes ago, Merlin66 said:

Many older objectives were cemented together with Canadian Balsam

Good information to know :)

This particular lens is new, so I'm taking a punt that it is the UV type glue.

Anyway, I have the acetone, and have just ordered :
https://www.ebay.co.uk/itm/New-5-Second-UV-Light-Fix-Liquid-Plastic-Welding-Compound-Glue-Repair-Pen-Tool/264447738745?hash=item3d92504379

We'll see when it comes 🌝

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Are you sure that they are optically misaligned?  They may be physically out but the optical centres may be coincident.    🙂

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Peter makes a good point - have you actually tried using it ?

Saying that, I had an Omni 4mm plossl a few years back with just the same issue. It came with a scope that I bought.

I ended up chucking the eyepiece out. I figured it was worth about £10 on the used market when in good shape so not worth all the hassle of trying to split and re-cement the faulty doublet element.

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8 hours ago, johninderby said:

You can get the proper stuff from Edmund Optics.

Thanks John; you were correct ... and the link is definitely worth bookmarking.

 

4 hours ago, Peter Drew said:

Are you sure that they are optically misaligned?  They may be physically out but the optical centres may be coincident.

This is an excellent thought; and to be honest ... I had not considered this outcome.

My best estimate is that it doesn't apply to this eyepiece.

From a manufacturing perspective, 'laser axial alignment' is possible.
However, it would be vastly more expensive than simple physical alignment.

The high end optics probably get that treatment, and perhaps even 'tolerance blueprinting' of components.

More likely, this error was noticed (at least by the operator or QC).
Note how it is not edge blacked !
This doublet lens was sticking out like a sore thumb ;)

Depending upon failure rates, it could be either recylced, placed in the B channel, or passed.
(I'm not stating that there IS a B channel)  :)
 

2 hours ago, John said:

have you actually tried using it ?

Yes.
But without a lab setup, and a standardised 4mm Omni Plossl, I can't know the comparative image error.

There were a number of issues noted, though in a test environment that was not ideal.
... yet enough to cause me to examine the eyepiece, and look for solutions.

I can understand the concept of 'binning it'.
However, this is a project, rather than a 'purchase and go'.
Consequently, the issue does fit the bill ... though it is bloody annoying, at this moment in time.

Of course; afterwards it will be great.
Brownie points cascading down in my direction, and the chance to round off a video with :

  "... a tricky job, but you can do it. That's how you do it..."

Hahaha!

Regardless though; I see the real benefit of building a scope, being that it creates a constant learning stream, that would otherwise be missed.

UV bonding and de-bonding being just one of many lessons learned.
... not in abstract, but true learning.

The other issue, relates to the fundamental fact, that mass produced kit often has a much greater potential than is realised by the production process.
A touch here and there, can very often produce a far superior end product.

There are risks ... but in a worst case scenario, the cost element is very low (and usually the risk pays off).
... and I have one such risk identified.

I think that another thread is in order 🌝

 

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