colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2170
Loc: CA
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Sorry that part 2 of my article has taken so long. I ran into some troubles with organizing all of the information. Hopefully I have presented it in a readable format. When I started writing this article I was completely unaware that this information was not in the public domain. The first time I used a DayStar etalon the entire stack was explained to me in detail so I assumed everyone knew how they were constructed. Hopefully I have also conveyed a little of the artistry making one of these filters requires.
http://www.designerinlight.com/solar/EtalonArticlePt2.pdf
Thank you to Mark, Gregg, Bob, Dave and Jen for providing input.
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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Solar B
Pooh-Bah
Reged: 02/28/07
Posts: 1025
Loc: By Edinburgh , Scotland
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Very good on the solid etalons Colin,something i have no experience of,so ive just printed a copy.
Brian
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" Gentlemen only ever use Refractors "
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Keith Howlett
Pooh-Bah
Reged: 03/06/07
Posts: 1029
Loc: Northumberland, UK
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Hi Colin,
It's a great article, many thanks!
Cheers,
Keith
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BYoesle
Pooh-Bah
Reged: 06/12/04
Posts: 1199
Loc: Goldendale, WA USA
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Great article! 
Please have a link posted in the Solar Resources thread.
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Bob Yoesle 
You are a child of the universe,
no less than the trees and the stars...
And whether or not it is clear to you,
no doubt the universe is unfolding as it should.
Desiderata
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Gene Baraff
sage, 1930-2010, Rest In Peace
Reged: 03/22/09
Posts: 265
Loc: Berkeley Heights, N.J.
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onderful article. I had been impressed by Part I but Part II is even more informative. The information about the mica birefringence and how it is tamed by polarizers is something I never would have thought about, even though I knew that mica was used because of its planar cleavage properties.
One point I wonder about though: you refer to the Lunt etalons as being solid. It is true that the spacer between the two mirrors is solid - fused silica - but the dielectric between the two mirrors is air.
That means that the detuning curve - the amount of wavelength shift you get per unit of tilt - is large, like the Coronado filters and not small, like the Daystar filters.
What then is the essential difference between the Lunt filters and the Coronado Solar Max's for example?
Gene Baraff
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gpiepol
Sungazer
Reged: 05/06/03
Posts: 1167
Loc: Maryland USA
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A truly wonderful resource for everyone, Colin.
Thank you!
Greg Piepol
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http://www.sungazer.net
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2170
Loc: CA
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Hi Gene,
All of the Lunt etalons in production are airspaced. However, Andy did mention to me that he has made fused silica etalons before and the option was on the table to do it again. I had not communicated to him for about 9 months and just last week I asked again about the posibility of a solid etalon from Lunt and was told it is still on the table and might be considered for the LS200.
The main difference between the airspaced filters is in the spacer technology. I tried to cover it in part one of the article but Lunt's were not shipping when I wrote part 1. Part one was the first place that the root 3 spacer system had been described. Here is the link to part 1:
http://www.designerinlight.com/solar/EtalonArticlePt1.pdf
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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Sol
Carpal Tunnel
Reged: 08/20/07
Posts: 2045
Loc: Powys, Wales, UK
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Excellent article Colin! I am not particularly interested in the technical side of solar optics, but have to admit that this was a good read - thanks for taking the time to put that together.
Mark
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Visit the Sunnymeade Astro Solar Blog
http://sunnymeadeastro.blogspot.com/
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Gene Baraff
sage, 1930-2010, Rest In Peace
Reged: 03/22/09
Posts: 265
Loc: Berkeley Heights, N.J.
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Yes, I remember your mentioning that in Part I, but the significance of the root 3 system (which I suspect is code for how far the spacers are separated relative to the radius of the filter) was not clear to me at that time.
Can you give a bit more detail?
Often, when one analyzes the condition for minimzing flexure of a structure by supporting it at a three points, root 3 enters into the geometricl considerations. Is that what is being described here?
Gene Baraff
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Gene Baraff
sage, 1930-2010, Rest In Peace
Reged: 03/22/09
Posts: 265
Loc: Berkeley Heights, N.J.
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Sorry. I just reread my copy of your Part I. You do explain perfectly clearly what the root 3 system means.
Gene
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Oldfield
Postmaster
Reged: 03/20/02
Posts: 5889
Loc: Hong Kong
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thank you!
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The Home Astronomer from a city where most people are proud of the light pollution
Toys: Orion 100ED, Ranger with NGF-CM, SM40/BF10, TG-SP II, LXD55, DMK 31AF03, Lumenera LU070M, Canon 10x30 IS...
My observation log and ideas My General Blog
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Tom and Beth
scholastic sledgehammer
Reged: 01/08/07
Posts: 946
Loc: Tucson, AZ
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Thank you for taking the time to do this "white paper". It explains the science and ART behind these much more understandable.
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Wee.Nghee
member
Reged: 08/09/06
Posts: 66
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thank you!
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bob71741
super member
Reged: 02/16/08
Posts: 123
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Colin - Thanks for another great informative article!!
I noticed that you included Angus Macleod's book in the references; every time I go to the library, the book is checked out. I was wondering if he discusses what the practical minimum bandwidth would be for a thin-film,
H-alpha filter.
Regards
Bob
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2170
Loc: CA
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I was only able to read excerpts from the book so I can't address that reference explicitly. However we often see .2A filters. If we leave etalon technology then we see filters in the .01A range. I have read of a few observatories with .05A tunable filters. I don't have the information handy but I believe the Ziess Universal Birefringent Filter was .05A and tunable through the entire visable range. It used Calcite Birefringent Elements to tune out orders. It would have to be at least a foot long or so and would have used lots of polarizers making the light throughput very low. I really like the technology of the Birefringent filters and am planning to write up something. First I want to address Solar Telescope Safety. I have been collecting notes for a Safety article for about a year.
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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Jim Rosenstock
Post Laureate
Reged: 07/14/05
Posts: 4195
Loc: MD, south of the DC Nebula
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Quote:
Thank you for taking the time to do this "white paper".
That's RED paper, pal!
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drake
sage
Reged: 11/08/08
Posts: 203
Loc: Naples, Italy
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thank you!
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Geremia
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Gene Baraff
sage, 1930-2010, Rest In Peace
Reged: 03/22/09
Posts: 265
Loc: Berkeley Heights, N.J.
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There is a monograph from long ago - "How to Build a Quartz Monochromator" by Richard B. Dunn, Harvard College Observatory, published by Sky Publishing Corporation (yep - the Sky and Telescope publishers)
It is a reprint of an article from Sky and Tel, Voume X, 1950-1951, from its department for amateru telescope makers, "Gleanings for ATM's".
Judging from the pictures accompanying the article (all of proms, none of the disk itself) it's not nearly narrow band enough for what you were talking about.
But what with your interest in the subject, this might be an interesting reference for you, if it is not already in your collection of papers.
Gene Baraff
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marktownley
Carpal Tunnel
Reged: 08/19/08
Posts: 2865
Loc: West Midlands, UK
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Fascinating articles Colin, thanks for sharing. 
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2170
Loc: CA
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Hi Gene,
I was lucky enough to have that article sent to me. If you want to cut the bandpass in half all you need to do is add another quartz element that is twice as large as the previous element. In quartz this is quite large, if I remember correctly the final stage was about 2.5". Finding optical grade quartz 5 or 10 inches thick is no easy task. Then you need to find the optical axis and polish the ends. Not to mention that this foot long object needs to be temperature controlled. I will look into it all more in a year or two. If you are very skilled at polishing the better solution is to use calcite because it's birefringence is larger and you can use smaller elements. However calcite is water soluble and very soft making polishing very different that an ATM is used to.
I think an easier approach for very narrow bands is a spectrohelioscope but the mechanicals require a fair amount of machine skills. For a company like Lunt making one that could do all visible wavelengths to .1A would only be $20K to $30K retail. I have been slowly collecting parts to construct one. I have all of the optics and a small lathe but no time.
--------------------
Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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