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a10ken

lunt b/f fogging

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hi folks, i have just experienced the lunt blocking filter lens fogging problem, bresser are posting a replacement so i thought i would have a look at the problem lens myself, well under a magnifying glass (10x) the opaqueness looked like bacteria on a petri dish, so i removed it and cleaned it of thoroughly (both sides) using autoglym bike visor cleaner and a cotton bud, followed by a rinse in cold water and dried of with a clean lint free cloth very successful and it is now perfectly clear...:happy2:

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CLR has also been used to "recover" failed Lunt ITF filters.....

 

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16 minutes ago, Merlin66 said:

CLR has also been used to "recover" failed Lunt ITF filters.....

 

I have heard the same thing about similar products for cleaning those pieces of bluish green glass, but i have not tried myself

 

Edited by OnceWaser

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The lunt blocking filter design uses a Schott BG38 blue glass element to replace the original ITF designed element.

Coronado still use an ITF design.

Both unfortunately are prone to deterioration, thought to be caused by moisture ingress. It's recommended that the BF be stored in an air-tight container with silica gel when not in use....

 

Edited by Merlin66
correction

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Just discovered this problem on the society Lunt and ordered a replacement at $7.95 USD, so a cheap fix.

I believe it is the coating degrading. Would wiping this off to remove the coating somehow affect the image? What was the point of the coating to begin with?  

Lunt_diagonal.JPG

Edited by Stu Todd

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13 hours ago, Merlin66 said:

CLR has also been used to "recover" failed Lunt ITF filters.....

I assume CLR is Calcium Lime Remover.

13 hours ago, OnceWaser said:

I have heard the same thing about similar products for cleaning those pieces of bluish green glass, but i have not tried myself

I tried Viakal on my Lunt LS60 blue filter once I received a replacement from Bresser (as I had nothing to lose) and it cleaned up nicely so now I have a spare.

A visual inspection did not suggest any damage to the filter but I haven't used it since the replacement was fitted, just put it somewhere safe with silica gel to use as a spare when the need arises. 

38 minutes ago, Stu Todd said:

Just discovered this problem on the society Lunt and ordered a replacement at $7.95 USD, so a cheap fix.

I believe it is the coating degrading. Would wiping this off to remove the coating somehow affect the image? What was the point of the coating to begin with?  

Lunt_diagonal.JPG

I seem to remember reading that the Lunt blue filters aren't coated but are just a particular type of blue glass as @Merlin66 suggests above.

Ha, found it. 

 

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Well, a bottle of CLR is cheaper than international postage. BTW, Lunt are having issues with their website. To get a $7.95 small glass out to me was $135. Before pressing the "OK" button, ask them to check!

I'd like to know what is "chemically unstable" though as glass itself can't be really. There must be an agent there?

 

Edited by Stu Todd

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Stu,

It's the chemical makeup up of the glass, it can be hydroscopic and absorb moisure.

The older green photometric filters had the same problem.

 

I thought Lunt were automatically replacing failed filters at no charge????

 

 

Edited by Merlin66

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Hi Ken,

The scope is nearly 10 years old so Lunt won't replace the glass. It is a very cheap fix anyway so that's no problem.

Quote from my conversations with them directly - "we have heard of a few customers having success with CLR (Calcium Lime Rust- Bathroom Cleaning Product) and products akin to it. As well, it is possible to take a new straight razor and scrape off the coating though that tends to make people a little more uncomfortable than not"

I'm off to buy some bathroom cleaner and a razor blade 😅

  • Thanks 1

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free replacement received from bresser, i will keep that as a spare, old one cleaned up perfectly with m/c visor cleaner.

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