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Cleaning the blue filter BF Lunt

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#1 lorenzo italy

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Posted 29 November 2020 - 05:44 AM

Goodmorning everyone,
this morning I was ready for the shooting of the great sunspot, but unfortunately the cloudy sky didn't help me ...
So I decided to try cleaning the blue filter of my BF 1200 of the Lunt 60mm telescope.

I have owned it for eight years now, and for over a year it had begun to degrade.
It started with a small spot on the surface, which got bigger over time.
Then lately other blurred areas have appeared, so much so that I began to suspect a degradation of the image of the Sun.
So I got myself a wrench to disassemble the sealing ring, which very easily unscrewed.
It can be said that it was just pulled, and the glue used to block it no longer held.
I then used a product for cleaning and polishing the plastic parabolas of automotive headlights, a product similar to others which, however, are not easily found in Italy.
With a cotton cloth I passed the polishing cream several times, and rubbed with light pressure.
At the end of the operation the filter appears shiny, even if observing it with the right angle of light one can still see a residue of the opacity.
But anyway now I have a more transparent filter than before, I just wait for the Sun to test it.

I still have a spare blue filter, sent to me free by Lunt, but I wanted to try the home polish to see the result.

 

Lorenzo

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#2 rigel123

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Posted 29 November 2020 - 06:07 AM

Good luck Lorenzo, it certainly looks clean now!


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#3 manusfisch

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Posted 29 November 2020 - 06:43 AM

Lorenzo, what do you think the film you cleaned off is composed of? I had assumed it was a degradation of the coating of this particular Lens construction

#4 vincentv

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Posted 29 November 2020 - 01:51 PM

This filters have no coating. What you see is the glass itself reacting with humidity. The manufacturer, Schott, actually recommends coating the glass to provide a protective layer. It's rumored that the new replacements from Lunt are coated, I haven't read of anyone confirming this.


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#5 lorenzo italy

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Posted 29 November 2020 - 01:55 PM

I don't know, it seems that due to humidity this patina is created on the filter.
However in various ways it can be eliminated, or Lunt sends you a replacement.

Fortunately, after noon the fog lifted, so I tried to record the Sun with the telescope, so as to see if the work on the filter was correct.
In the eyepiece the Sun was very nice and bright, even though I was using the telescope in double stack mode.
I then shot with a ZWO ASI178mm camera, processing the videos with Autostakkert3 and Astrosurface.

 

Lorenzo

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#6 lorenzo italy

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Posted 29 November 2020 - 01:56 PM

Close-up

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#7 PhotonJohn

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Posted 29 November 2020 - 02:38 PM

Beautiful images Lorenzo, looks your cleaning helped.
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#8 bigdob24

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Posted 29 November 2020 - 08:13 PM

Nice clean images


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#9 briansalomon1

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Posted 30 November 2020 - 11:38 AM

It looks like the "Rinnova Finale" is a fine polishing compound. That would have been the very last thing I would have advised but if it works there is no arguing against it.

 

A more conservative method is to clean the filter with Acetone followed by >90% Isopropyl alcohol. The rinnova compound left a film on the glass that can be removed with Acetone/alcohol and Q-tips.



#10 bigdob24

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Posted 30 November 2020 - 02:07 PM

I think cleaning is a last ditch effort to get by, I would think that once a filter corrodes and is cleaned chances are it’s not going to last as long. I would replace them as cheap as they are and look at different  storage  arrangements 



#11 DAVIDG

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Posted 30 November 2020 - 02:39 PM

  A new filter from Lunt is only $7.95.    When I sent my 60m Lunt in for service Lunt was nice enough to give my a new blue filter even thou mine was fine. I was told that the new filters are coated to prevent the corrosion issue.

 

               - Dave 


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#12 briansalomon1

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Posted 30 November 2020 - 03:09 PM

  A new filter from Lunt is only $7.95.    When I sent my 60m Lunt in for service Lunt was nice enough to give my a new blue filter even thou mine was fine. I was told that the new filters are coated to prevent the corrosion issue.

 

               - Dave 

Yeah, they're so inexpensive I keep a few as spares. I get that this is an absorbance filter and is seeing ~6 to 8 Watts but it seems odd that the glass structure would change from that level of energy.

 

Do you have any idea what the coating is? 



#13 lorenzo italy

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Posted 30 November 2020 - 04:12 PM

I think cleaning is a last ditch effort to get by, I would think that once a filter corrodes and is cleaned chances are it’s not going to last as long. I would replace them as cheap as they are and look at different  storage  arrangements 

You are right,
I already have the filter to replace, but I wanted to try polishing (as others have done before me) to see the result.
And above all how long the cleaning effect will last, or if the problem will recur quickly.

 

 

  A new filter from Lunt is only $7.95.    When I sent my 60m Lunt in for service Lunt was nice enough to give my a new blue filter even thou mine was fine. I was told that the new filters are coated to prevent the corrosion issue.

 

               - Dave 

Is it possible to know since Lunt has the new models of the blue coated filter?
My replacement is from 2017 ... I believe it is still the previous model.

 

Lorenzo



#14 lorenzo italy

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Posted 30 November 2020 - 04:19 PM

Yeah, they're so inexpensive I keep a few as spares. I get that this is an absorbance filter and is seeing ~6 to 8 Watts but it seems odd that the glass structure would change from that level of energy.

 

Do you have any idea what the coating is? 

I believe that it is not the energy that the filter receives from the telescope that degrades it, but that it is the humidity that degrades the surface of the filter.
I had read this in various posts,
where in fact it was recommended to keep the BF in a dry place ...
Mine is now 8 years old, there can be degradation.

 

Lorenzo




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