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Unmounted Glass Solar Filter?

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#1 pbealo

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Posted 19 February 2019 - 03:45 PM

Hi all,

 

I have a couple solar filter cells for "classic" telescopes.

 

Any suggestions who I could approach about unmounted GLASS solar filters to fit into these cells.

 

1 cell requires ~ 6.25" filter, the other ~4.25".

 

Peter

 

 



#2 BYoesle

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Posted 19 February 2019 - 04:28 PM

Why GLASS?

 

To get a good optical quality filter in that size would be pretty expensive - perhaps Zeiss, or use a Baader 160 mm (for 6.25 cell) DERF and coat it with a standard aluminum coating at 96% reflectivity, use additional ND filters to get the image brightness right.

 

Otherwise just get a float glass filter from Thousand Oaks.

 

The best thing would be to use the cells to mount some Baader Astrosolar filter material. Cheap, easily replaced, and better than float glass filters.


Edited by BYoesle, 19 February 2019 - 04:29 PM.


#3 Don W

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Posted 19 February 2019 - 11:22 PM

Agreed. Go with Baader Astrosolar film and cut it to fit. Attach with double sided tape.



#4 DAVIDG

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Posted 20 February 2019 - 09:52 AM

 I think Peter wants to use glass because they are for a vintage telescope and wants to try to keep things close to original.  What you need is high quality glass that then can be coated to make a solar filter. Most of the glass filters on the market are made with low quality glass hence they give substandard images vs Baader film or high quality glass filters like what Questar and Zeiss have offered. Cumberland Optics made the glass substrate for the Questar and Quantum solar filters. 

    I would look for surplus camera filters and/or optical windows especially government surplus ones. I have a number of red Kodak filters from WWII camera that are optically excellent, that I  use as ERFs. To test them you place them in front of spherical mirror and test the mirror via a Foucault or Ronchi test to look for any chances. Another possibility is to purchase a large piece of float plate glass and scan it via the spherical mirror test and find any good areas and then cut them out and have them coated. 

 

               - Dave 


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#5 pbealo

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Posted 21 February 2019 - 07:14 AM

Dave is correct: the cells are for Quantum 4 and 6 telescopes. They're made for glass, though I could make something to hold solar filter material.

 

Peter




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