SolarMax internal etalon size (old SM70 and SM90II)

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SolarMax internal etalon size (old SM70 and SM90II)

Post by Pablito » Tue Aug 16, 2016 5:39 pm

Hello,

Does anyone know what size have internal etalons in SolarMax 70 (old model) and SolarMax 90 II?

I know that SM 60 II has 35mm aperture with central obstruction. What about others? I have old SolarMax 70 on my eye but know nothing about it and I'm not sure how it will work in bigger aperture mod. It's focal ratio almost fits my 5" refractor.

Thanks for any help :)

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Bob Yoesle » Tue Aug 23, 2016 5:40 am

Hi Pablito,

The SolarMax 70 was the same as the Helios (I think); I believe it is a ~ 50 mm OD etalon with a clear aperture of 35 mm - almost identical to the current Lunt 60 internal etalon in that regard. I don't have any idea on the current SM90II, but I believe the original (Tucson) SM90 internal module etalon was an SM60.
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Pablito » Tue Aug 23, 2016 10:07 am

Thanks Bob, it helps me much :)

Do you kow why Lunt or Coronado cut clear aperture in internal etalons?

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Bob Yoesle » Tue Aug 23, 2016 5:29 pm

Hi Pablito,

The internal etalons Coronado and Lunt use are air-spaced etalons:

In the solid spacer type of etalon, the mirror coating is applied to the ends of the solid material - cleaved mica in the case of the DayStar and Solar Spectrum filters. Therefore the entire face of the filter is usually coated, and the "etalon gap" is the substrate itself.

With the air-spaced etalons (Coroandao, Lunt, Solar Scope) the interfering reflections occur between the inside faces of the optically polished etalon plates, and they are separated by very thin low-expansion spacers, which are small chips broken off from a larger uniformly thin wafer of polished low-expansion glass (see below). These multiple spacers must be optically contacted ( https://en.wikipedia.org/wiki/Optical_contact_bonding ) to the un-coated faces of the mirror substrates around the periphery - therefore the mirror coating does not extend all the way to the edge of the substrate, and the etalon is effectively smaller than the substrate itself.

Coronado patented the use of a central spacer to maintain the etalon gap spacing under changing thermal loads encountered in solar observation, and Lunt patented the "Root 3" three central spacer method to do the same thing in it's larger 100 mm etalons. These spacers are also optically contacted between un-coated areas of the substrate, and therefore require a reflective "mask" in front and behind the uncoated area to prevent stray and direct sunlight from getting through.

The Coronado SM90 etalon has an effective coated diameter of 90 mm, the optical substrates themselves are 105 mm in diameter:
SM90 s ERF crp SM.jpg
SM90 s ERF crp SM.jpg (286.16 KiB) Viewed 2983 times
Hope this helps. B-)
Last edited by Bob Yoesle on Tue Aug 23, 2016 10:14 pm, edited 1 time in total.
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Valery » Tue Aug 23, 2016 6:39 pm

Bob Yoesle wrote:Hi Pablito,

The SolarMax 70 was the same as the Helios (I think); I believe it is a ~ 50 mm OD etalon with a clear aperture of 35 mm - almost identical to the current Lunt 60 internal etalon in that regard. I don't have any idea on the current SM90II, but I believe the original (Tucson) SM90 internal module etalon was an SM60.
Thanks a lot, Bob!

Much appreciated.


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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Pablito » Tue Aug 23, 2016 7:25 pm

All is clear now. Thank you very much Bob!

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Bob Yoesle » Tue Aug 23, 2016 9:51 pm

You're very welcome Valery and Pablito ;-)

BTW, here's some interesting and I hope informative pics I got on my March 2015 visit to Lunt which shows some of what goes into making today's H alpha solar telescopes:

On the way down, beautiful Arizona desert scenery:
IMG_20150323_162618757 crp SM.jpg
IMG_20150323_162618757 crp SM.jpg (103.98 KiB) Viewed 2966 times
The optical components are polished flat on large orbital polishers; note the grey tube at upper right which supplies the polishing slurry to the huge rotating polishing lap. The large central weight deforms the lap as needed to produce the desired polishing shape:
Polishing.jpg
Polishing.jpg (121.07 KiB) Viewed 2966 times
Spacer discs are attached to larger discs for polishing to the precise thickness required for the etalon gap:
Spacer polishing.jpg
Spacer polishing.jpg (58.42 KiB) Viewed 2966 times
A LS60 etalon plate with mirror coating:
Coated plate.jpg
Coated plate.jpg (74.18 KiB) Viewed 2966 times
Multiple etalon plates grouped and awaiting assembly:
Etalon plates.jpg
Etalon plates.jpg (94.65 KiB) Viewed 2966 times
A spacer disc with portions removed for spacer assembly placement:
Spacer chips.jpg
Spacer chips.jpg (85.47 KiB) Viewed 2966 times
Spacer assembly testing station:
Spacer etalon assembly sm.jpg
Spacer etalon assembly sm.jpg (62.31 KiB) Viewed 2966 times
Workstation for spacer placement and etalon assembly:
IMG_20150323_111451219_HDR crop SM.jpg
IMG_20150323_111451219_HDR crop SM.jpg (89.93 KiB) Viewed 2966 times
Completed LS60 etalon (camera focused on ceiling tiles!):
completed etalon.jpg
completed etalon.jpg (71.06 KiB) Viewed 2966 times
Checking an etalon fringe pattern using a laboratory Hydrogen spectrum tube:
Test crp SM.jpg
Test crp SM.jpg (57.47 KiB) Viewed 2966 times
In-house CNC machining of OTA components:
Raw and finished.jpg
Raw and finished.jpg (118.97 KiB) Viewed 2966 times
Pressure tuners being assembled:
Pressure tuner assembly.jpg
Pressure tuner assembly.jpg (137 KiB) Viewed 2966 times
A tilt-tuned etalon in it's "basket cell":
Tilt tuned etalon.jpg
Tilt tuned etalon.jpg (121.47 KiB) Viewed 2966 times
Finished LS50's and 60's awaiting final testing an shipment:
Awaiting final testing.jpg
Awaiting final testing.jpg (104.91 KiB) Viewed 2966 times
On my way home through the Nevada Great Basin - wonderful dark-skies ;-)
IMG_20150324_145805848 crp SM.jpg
IMG_20150324_145805848 crp SM.jpg (321.77 KiB) Viewed 2966 times
Thanks again to all the wonderful folks at LUNT Solar for their help and hospitality!

B-)
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Pablito » Wed Aug 24, 2016 1:41 pm

WOW! :)

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Marcello » Fri Aug 26, 2016 1:39 pm

Hi Bob, very interesting report, thanks!

The reflection of the ceiling is impressive!
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by marktownley » Fri Aug 26, 2016 10:44 pm

A good story there Bob! :)
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Valery » Sat Aug 27, 2016 5:02 pm

Thanks, Bob, for the story.


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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by christian viladrich » Mon Aug 29, 2016 12:00 pm

Thanks Bob for sharing these images !
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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by christian viladrich » Tue Oct 04, 2016 8:31 pm

BTW, an information there ... I don't know if it is relevant at all in the discussion :
- in an "optimal" system, the F/D of the refractor lens (or telescope) should be equal to the f/d of the divergent (or convergent) lens of the collimating system,
- once this is true, the radius of the sweet spot simply depends on the ratio : diameters of etalon /diameter of the etalon.
So the bigger the internal etalon, the larger the sweet spot, but of course there are some practical issues ....
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Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Valery » Tue Oct 04, 2016 10:29 pm

"diameters of etalon /diameter of the etalon." (C.V)

You, obviously, just mistaken, miswritten. Should be diameters of an objective/diameter of an etalon.

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Re: SolarMax internal etalon size (old SM70 and SM90II)

Post by Sungazer » Wed Oct 05, 2016 9:10 am

Many thanks Bob for the very informative photos of Etalon production. I had often wondered how they where manufactured. Quite a change from,The old system of half plates and Polaroid sheets interleaved ,which was used in the 1960s. D :bow2

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