SolarMax internal etalon size (old SM70 and SM90II)
SolarMax internal etalon size (old SM70 and SM90II)
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
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
- Bob Yoesle
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Re: SolarMax internal etalon size (old SM70 and SM90II)
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.
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)
Thanks Bob, it helps me much
Do you kow why Lunt or Coronado cut clear aperture in internal etalons?
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)
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:
Hope this helps. B-)
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:
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)
Thanks a lot, Bob!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.
Much appreciated.
Valery
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Re: SolarMax internal etalon size (old SM70 and SM90II)
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: 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: Spacer discs are attached to larger discs for polishing to the precise thickness required for the etalon gap: A LS60 etalon plate with mirror coating: Multiple etalon plates grouped and awaiting assembly: A spacer disc with portions removed for spacer assembly placement: Spacer assembly testing station: Workstation for spacer placement and etalon assembly: Completed LS60 etalon (camera focused on ceiling tiles!): Checking an etalon fringe pattern using a laboratory Hydrogen spectrum tube: In-house CNC machining of OTA components: Pressure tuners being assembled: A tilt-tuned etalon in it's "basket cell": Finished LS50's and 60's awaiting final testing an shipment: On my way home through the Nevada Great Basin - wonderful dark-skies ;-) Thanks again to all the wonderful folks at LUNT Solar for their help and hospitality!
B-)
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: 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: Spacer discs are attached to larger discs for polishing to the precise thickness required for the etalon gap: A LS60 etalon plate with mirror coating: Multiple etalon plates grouped and awaiting assembly: A spacer disc with portions removed for spacer assembly placement: Spacer assembly testing station: Workstation for spacer placement and etalon assembly: Completed LS60 etalon (camera focused on ceiling tiles!): Checking an etalon fringe pattern using a laboratory Hydrogen spectrum tube: In-house CNC machining of OTA components: Pressure tuners being assembled: A tilt-tuned etalon in it's "basket cell": Finished LS50's and 60's awaiting final testing an shipment: On my way home through the Nevada Great Basin - wonderful dark-skies ;-) 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)
Hi Bob, very interesting report, thanks!
The reflection of the ceiling is impressive!
The reflection of the ceiling is impressive!
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Re: SolarMax internal etalon size (old SM70 and SM90II)
A good story there Bob!
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Re: SolarMax internal etalon size (old SM70 and SM90II)
Thanks, Bob, for the story.
Valery
Valery
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Re: SolarMax internal etalon size (old SM70 and SM90II)
Thanks Bob for sharing these images !
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Re: SolarMax internal etalon size (old SM70 and SM90II)
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 ....
- 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 ....
Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
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Re: SolarMax internal etalon size (old SM70 and SM90II)
"diameters of etalon /diameter of the etalon." (C.V)
You, obviously, just mistaken, miswritten. Should be diameters of an objective/diameter of an etalon.
Valery
You, obviously, just mistaken, miswritten. Should be diameters of an objective/diameter of an etalon.
Valery
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.
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Re: SolarMax internal etalon size (old SM70 and SM90II)
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