Fixing Baader-U with crack

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johan
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Fixing Baader-U with crack

Post by johan »

So I just bought a 2" Baader-U with a crack for £35 which I am rather pleased with CONSIDERING THE BLOODY THINGS COST NORTH OF £250 NEW! Shout over :)

So it has the tiniest of tiny cracks, barely visible in this (terrible phone) photo:

Image

So I'm wondering, it's a hairline crack, I think I can probably get away with a very thin accurate slice of gorilla tape over both sides.

But curious if anyone has tried this/found a more cost effective solution OR indeed if the filter will degrade because of exposure to air?

Thanks
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My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.

enricosavazzi
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Post by enricosavazzi »

Degradation of the filter glass does take place with exposure to air and humidity, but is generally a slow process. If you use this filter on a lens with a small front element (so that the filter behaves in practice like a 1.25" filter) and no further mishaps happen to the filter, it should give you many years of service.

Note that the filter glass should be loosely mounted in the metal ring. It is OK if it rattles a little when shaken. Tightening the retaining ring is one of the ways these filters can be cracked.

To protect the cracked portion my first thought would be using a fluid glue/sealer with high capillarity, so that it penetrates the crack. Something like a cyanoacrylate for optics. Ordinary instant cyanoacrylate glue leaves a halo of white sublimate around the original drop, which can be difficult to clean away.
--ES

johan
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Post by johan »

Great, thanks Enrico, appreciated
My extreme-macro.co.uk site, a learning site. Your comments and input there would be gratefully appreciated.

ChrisR
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Post by ChrisR »

The "stuff" for repairing car windscreen cracks might be suitable and easy to get?
Chris R

dolmadis
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Post by dolmadis »

What about this optical adhesive from Edmunds?

"Norland Optical Adhesive 61 ("NOA 61") is a clear, colorless, liquid photopolymer that will cure when exposed to ultraviolet light. Since it is a one part system and 100% solids, it offers many advantages in bonding where the adhesive can be exposed to UV light. The use of NOA 61 eliminates premixing, drying or heat curing operations common to other
adhesive systems. Curing time is remarkably fast, and is dependent upon the thickness applied and the amount of ultraviolet light energy available.

NOA 61 meets Federal Specification MIL-A-3920 for optical adhesives and is approved for use on all government contracts specifying such adhesives. The adhesive is designed to give the best possible optical bond to glass surfaces,
metals, fiberglass and glass filled plastics. NOA61 is recommended for bonding lenses, prisms and mirrors for military,aerospace and commercial optics as well as for terminating and splicing optical fibers.

NOA 61 also has excellent clarity, low shrinkage and as light flexibility that make it superior to other materials for optical bonding. These characteristics are important in order for the user to produce high quality optics and achieve long term performance under changing environments."

enricosavazzi
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Post by enricosavazzi »

ChrisR wrote:The "stuff" for repairing car windscreen cracks might be suitable and easy to get?
Don't know whether it would be appropriate in this case, but it is a possibility.

And of course letting it penetrate cracks after placing the item in a vacuum/low pressure enclosure is likely to improve capillary penetration of cracks for any non-volatile adhesive, not just windscreen crack filler.
--ES

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