Analysis of Fabry-Perot mica spaced Ha filters

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
Post Reply
User avatar
DSobserver
Almost There...
Almost There...
Posts: 542
Joined: Sun Feb 19, 2012 2:36 pm
Location: FRANCE

Analysis of Fabry-Perot mica spaced Ha filters

Post by DSobserver » Sat Jan 10, 2015 11:11 am

Here an interesting new analysis made by C.viladrich

http://www.astrosurf.com/viladrich/astr ... lar/FP.htm

User avatar
marktownley
Librarian
Librarian
Posts: 24536
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by marktownley » Sat Jan 10, 2015 11:49 am

Thank you for that link, it is very interesting and shows exactly my experience with the Quark.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

User avatar
Bob Yoesle
Im an EXPERT!
Im an EXPERT!
Posts: 473
Joined: Thu Mar 08, 2012 7:24 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Bob Yoesle » Sat Jan 10, 2015 2:12 pm

An excellent analysis!

I especially appreciated the citation of Gene Baraff's work on the importance of using properly optimized telecentric lenses matched to the focal length of the objective - something generally not fully appreciated with these filters -- and why DayStar rightly does not provide a FWHM figure for the Quark.
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by swisswalter » Sat Jan 10, 2015 6:59 pm

Hi Vincent

thank you very much for the link. Tons of good pages to read, very informative
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

pbsastro
The Sun?
The Sun?
Posts: 12
Joined: Sat Jan 10, 2015 1:15 am

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by pbsastro » Thu Jan 15, 2015 1:39 am

Bob Yoesle wrote:An excellent analysis!

I especially appreciated the citation of Gene Baraff's work on the importance of using properly optimized telecentric lenses matched to the focal length of the objective - something generally not fully appreciated with these filters -- and why DayStar rightly does not provide a FWHM figure for the Quark.
Yes, very interesting. I will need to read it carefully, but that makes important to confirm the Baader telecentric ideal FL. Bob, you mentioned 800mm at CN. Can you confirm that? I will be using it with 1400mm which would make it only acceptable, not very good.
In any case I think the edge degradation should be determined on the field edge, not sun edge, as on most scopes (specially on the 1400mm one), we can't get the full sun.

Pedro

mdwmark
Ohhhhhh My!
Ohhhhhh My!
Posts: 127
Joined: Tue Mar 04, 2014 6:13 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by mdwmark » Sat Jan 17, 2015 8:17 am

The data looks good to me. There is nothing magical about F/30. It was just convenient in the early days because most scopes where F/15. To get to .3Ang you are usually starting below that. But you really need to be F/45 or longer. You will not get to .3Ang at F/30 regardless what you start with. The mica etalon does have the advantage over an air spaced etalon for a larger (sweet spot) at narrower bandwidths because of the difference in index of refraction.
Telecentric versus collimated:
Telecentric may broaden out the filter but it will broaden evenly. A collimated beam is easier to design but there's a wavelength shifts from the center to the edge. The HW will be the same, the center wavelength changes(shifts blue). Which gives you the sweet spot you see with this design. The sweet spot will be less noticeable the broader the HW is.
This is just how etalons work.
Mark W.

User avatar
Bob Yoesle
Im an EXPERT!
Im an EXPERT!
Posts: 473
Joined: Thu Mar 08, 2012 7:24 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Bob Yoesle » Sun Jan 18, 2015 3:05 am

Bob, you mentioned 800mm at CN. Can you confirm that? I will be using it with 1400mm which would make it only acceptable, not very good.
Hi Pedro,

That is the design focal length Mark Wagner provided - and he should know as the Baader telecentric units are made to be used with the Solar Spectrum line of filters.

Christian has posted another update to his first study, which shows once again the power of double stacking etalons, and how the CWL shifts with tilt for a collimated system. As Mark has stated this shift changes across the filter due to field angle magnification: http://www.astrosurf.com/viladrich/astr ... aystar.htm

In an optimized telecentric system, you only deal with uniformly broadened band-pass based on the F/D ratio light cone. In a non-optimized telecentric system, you likely will face both band-pass broadening and CWL shifting.
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by swisswalter » Sun Jan 18, 2015 8:53 am

Hi Bob

thanks for the additional link
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3053
Joined: Sun Nov 18, 2012 3:13 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Valery » Sun Jan 18, 2015 5:02 pm

mdwmark wrote:The data looks good to me. There is nothing magical about F/30. It was just convenient in the early days because most scopes where F/15. To get to .3Ang you are usually starting below that. But you really need to be F/45 or longer. You will not get to .3Ang at F/30 regardless what you start with. The mica etalon does have the advantage over an air spaced etalon for a larger (sweet spot) at narrower bandwidths because of the difference in index of refraction.
Telecentric versus collimated:
Telecentric may broaden out the filter but it will broaden evenly. A collimated beam is easier to design but there's a wavelength shifts from the center to the edge. The HW will be the same, the center wavelength changes(shifts blue). Which gives you the sweet spot you see with this design. The sweet spot will be less noticeable the broader the HW is.
This is just how etalons work.
Mark W.
Hi Mark,

What must be the F/D of a telecentric system that Solar Spectrum 0.2A etalon will really deliver these 0.2A ?
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

User avatar
marktownley
Librarian
Librarian
Posts: 24536
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by marktownley » Sun Jan 18, 2015 9:38 pm

I have to say Christians work on this paper is one of the best resources available for pulling things together mathematically in a way that has been discussed loosely on the web for sometime now. The more I digest it the more it makes me think.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

pbsastro
The Sun?
The Sun?
Posts: 12
Joined: Sat Jan 10, 2015 1:15 am

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by pbsastro » Wed Jan 21, 2015 1:09 am

Bob Yoesle wrote:
Bob, you mentioned 800mm at CN. Can you confirm that? I will be using it with 1400mm which would make it only acceptable, not very good.
Hi Pedro,

That is the design focal length Mark Wagner provided - and he should know as the Baader telecentric units are made to be used with the Solar Spectrum line of filters.

Christian has posted another update to his first study, which shows once again the power of double stacking etalons, and how the CWL shifts with tilt for a collimated system. As Mark has stated this shift changes across the filter due to field angle magnification: http://www.astrosurf.com/viladrich/astr ... aystar.htm

In an optimized telecentric system, you only deal with uniformly broadened band-pass based on the F/D ratio light cone. In a non-optimized telecentric system, you likely will face both band-pass broadening and CWL shifting.
Thanks Bob. Then I think I will go with an optimized telecentric for my 1400mm refractor. The Baader will be good for my TV102.
I m also convinced to go double stacking, thanks to the double limb topics you have raised. Thanks! f I have been talking to Mark to see if can get me a double stack filter, he will check what he can do, in terms of reflections control, but it seems I will need two ovens/controllers.
Anyone wants to join me in this waggon :)

Pedro

mdwmark
Ohhhhhh My!
Ohhhhhh My!
Posts: 127
Joined: Tue Mar 04, 2014 6:13 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by mdwmark » Wed Jan 21, 2015 5:37 am

To get to .2Ang you are really starting below that. They are in the .1Ang range. The focal ratio should be up in the F/50- F/60 range. Unless you are doing Doppler work I don't see any reason to be that narrow. That is why I changed to .3Ang specs. At these narrow HW filters the substrates need to better then 100th wave. It becomes a matter of how nature made the mica and the type of mirrors you have on the substrate.
Unlike an air spaced etalon you only have one shot at it. You can't go back and re-polish the flats to a better surface.
The .3Ang filters, I try to have them in that range at F/45-F/50 range. But really a .3Ang filter at F/35 still shows good detail.
To get the image size back down you really just need to use a long focal length eyepiece. I have even used a old 130mm telephoto lens backwards as an eyepiece.
The one advantage of the mica etalon is that you can use it as a variable HW filter, just by changing the focal ratio( going faster you need to increase the temperature also because it has shifted blue).
Mark W.

User avatar
marktownley
Librarian
Librarian
Posts: 24536
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by marktownley » Wed Jan 21, 2015 6:52 pm

mdwmark wrote:The one advantage of the mica etalon is that you can use it as a variable HW filter, just by changing the focal ratio( going faster you need to increase the temperature also because it has shifted blue).
I'd not thought of it like this before... You have my tinkering mind working in overtime ;) Thanks Mark.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

User avatar
Bob Yoesle
Im an EXPERT!
Im an EXPERT!
Posts: 473
Joined: Thu Mar 08, 2012 7:24 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Bob Yoesle » Sun Feb 08, 2015 8:20 pm

Christian has updated his analysis with a good treatment of air-spaced etalons, and illustrates some practical applications:

http://www.astrosurf.com/viladrich/astr ... P-Coro.htm

Fantastic information - should be added to the Library I should think (hint Mark ;) )
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by swisswalter » Tue Feb 10, 2015 4:45 am

Thank you Bob
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

User avatar
Bob Yoesle
Im an EXPERT!
Im an EXPERT!
Posts: 473
Joined: Thu Mar 08, 2012 7:24 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Bob Yoesle » Sun Mar 29, 2015 9:02 pm

Christian continues to update his analysis of filter performance. Here's his latest, which gets to a question Ken had raised about how blocking filters affect bandpass, as well as mixing different primary FWHM's:

http://www.astrosurf.com/viladrich/astr ... ntrast.htm
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders

User avatar
marktownley
Librarian
Librarian
Posts: 24536
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by marktownley » Sun Mar 29, 2015 9:19 pm

Another great read from Christian!
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17951
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by swisswalter » Mon Mar 30, 2015 4:09 am

Hi Bob

thank you very much, most interesting
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

User avatar
Bob Yoesle
Im an EXPERT!
Im an EXPERT!
Posts: 473
Joined: Thu Mar 08, 2012 7:24 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Bob Yoesle » Fri Apr 10, 2015 8:27 pm

Christian just let me know he's added an update to the above Blocking Filter analysis - very interesting results using an DayStar 0.6 A with an Omega 4.5 A used as a BF... http://www.astrosurf.com/viladrich/astr ... ntrast.htm
Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders

User avatar
marktownley
Librarian
Librarian
Posts: 24536
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by marktownley » Fri Apr 10, 2015 9:24 pm

An interesting addition. I believe this is the principal of how I get the contrast gains that I do with my quark and naked PST etalon.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 3053
Joined: Sun Nov 18, 2012 3:13 pm

Re: Analysis of Fabry-Perot mica spaced Ha filters

Post by Valery » Sat Apr 11, 2015 12:14 am

One more excellent addition to Christian's book.


Valery
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

Post Reply

Who is online

Users browsing this forum: No registered users and 0 guests