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B1200 Potential Issue

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#1 Fish


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Posted 19 May 2013 - 07:28 PM

Good evening boys & girls,

Well, this was unexpected. I removed the B1200 Ha blocking filter from the observatory scope today and noticed this on the output (scope) side.

My questions are:
--> Anybody else seen this? It's more of a cloudy deposit than a "rust" and in the inside of the diagonal.
--> Is there an easy, safe way to get in? I see 2 hex set screws on the side.
--> I can't see how this wouldn't affect the performance of the scope as this must degrade the image.

Big surprise, I'm not all that pleased over this and hope it may be resolved simply.

Regards, Marc

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#2 bob71741



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Posted 19 May 2013 - 09:55 PM

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#3 DavidM


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Posted 20 May 2013 - 07:04 AM

Yep, had this problem with a B1200 and B1800. Possibly both were from the same batch. Lunt replaced them, no problems. This reminds me, I need to check the blocking filter again to make sure it hasn't happened again.

#4 Fish


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Posted 20 May 2013 - 04:51 PM


I spoke with Rikki. She is sending me a replacement glass for the filter. After speaking with her I feel the swap out is easy enough to avoid shipping the entire BF.

Now that's good customer service!


#5 dscarpa



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Posted 20 May 2013 - 07:25 PM

Yes I've seen it on my 2009 Lunt 60's B1200. There's no easy fix. As I recall it is rust. It does ideed degrade the image like a very hazy day. At any rate the only cure is new glass from Lunt. I'd be interested in seeing how you swap the glass if you feel like posting it. Save people some postage what with not having to send the diagonal back like I did. David

#6 BYoesle



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Posted 21 May 2013 - 11:24 AM

That's good news Marc!

As I recall it is rust.

I'm not so sure I'd call it "rust." "Rust" is what occurred with the Coronado Induced Transmission Filter (ITF) coating, which is an IR blocking coating using metallic silver and other materials to block to the far IR. Thermal cycling caused cracks in the filter's epoxy sealant around the edge, which allowed atmospheric moisture to degrade the coating, and therefor deterioration usually proceeded from the edge inward.

This appears different with deterioration towards the center of the filter. I'm not absolutely sure of this, but I believe Lunt has switched to a non-metallic/silver IR blocker - perhaps a KG heat absorbing filter or other material, which has AR coatings. Andy Lunt stated it is the AR coating on these filters that failed - due to processing deficiencies form their filter coater. This occurred with the early filters, and they now have changed filter coaters.

As you could imagine, additional requirements might be needed for the intended use of direct solar thermal exposure. So while the cause might be the same - thermal exposure - the Lunt issue appears to be coating degradation due to direct expsure to thermal energy, while the "rust" of the Coronado ITF was due to moisture deterioration.

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