Blocking Filter In a Collimated Beam?

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
Post Reply
User avatar
marktownley
Librarian
Librarian
Posts: 42272
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20435 times
Been thanked: 10243 times
Contact:

Blocking Filter In a Collimated Beam?

Post by marktownley »

Anyone ever tried placing a Coronado / Lunt blocking filter in a collimated beam to see if it trims down continuum leakage in the wings?


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!
bart1805
Almost There...
Almost There...
Posts: 636
Joined: Mon Feb 06, 2017 9:04 pm
Location: The Netherlands
Been thanked: 1 time

Re: Blocking Filter In a Collimated Beam?

Post by bart1805 »

Interesting question Mark! Hope somebody has tested it. In addition to that question: what is the effect in theory of tilting the Blocking filter? Will try it out, but curious what to expect.


User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by Merlin66 »

I was thinking of another approach...
What about a blocking filter double stack to reduce the FWHM and trim the etalon wings.....


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by Merlin66 »

Bart,
Tilting the blocking filter will move the CWL towards the blue, but won't change the FWHM result.


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Bob Yoesle
Almost There...
Almost There...
Posts: 994
Joined: Thu Mar 08, 2012 7:24 pm
Has thanked: 540 times
Been thanked: 807 times

Re: Blocking Filter In a Collimated Beam?

Post by Bob Yoesle »

"Anyone ever tried placing a Coronado / Lunt blocking filter in a collimated beam to see if it trims down continuum leakage in the wings?"

Hi Mark, not sure this would get much improvement. If the BF has a Lorentzian profile - just as with FP etalons - the main effect would be to improve field angle rays through the filter so they are not as blue-shifted out of band (e.g. the filter's Jacquinot spot would be enlarged), but I don't think it would do much to change the filter transmission profile.

As Ken notes, double stacking a blocking filter would probably have a greater effect to reduce the etalon's wings. We can see for the one measurement I know of the Coronado blocking filter does appear to have a Lorentzian profile with a peak transmission of about 65%, and a FWHM of 0.6 nm.

Cor-BF15Ha-zoom.gif
Cor-BF15Ha-zoom.gif (19.78 KiB) Viewed 4397 times

For a single stack Lorentzian the 1% transmission value is 10 x FWHM = 6 nm, and for double stacking the 1% transmission value is reduced to 3 x FWHM = 1.8 nm. Not sure this would be too significant. However, double stacking the blcoking filter would reduce transmission to about 42%, which would be significant.

More discussion can be found here:

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
Goldendale Observatory
User avatar
marktownley
Librarian
Librarian
Posts: 42272
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20435 times
Been thanked: 10243 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by marktownley »

Interesting thanks guys!


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!
christian viladrich
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2150
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Has thanked: 1 time
Been thanked: 2713 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by christian viladrich »

Hi Mark,
The question of tilt / collimated or telescentric beam starts to become an issue with filters narrower than about 2 to 3 A.
BF are usually about 5 to 10 A. So, it should not be a big issue.

Regarding stacking an etalon and a BF, I've done many tests. For example here with a top quality 1.5 A BF and a variety of etalons :
http://www.astrosurf.com/viladrich/astr ... -tests.htm

A 1.5A BF would require a TEC body. If ever you are interested in it, you can contact me through PM.


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by Merlin66 »

Christian,
Have you looked at double stacked blocking filters to trim the etalon wings??


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
christian viladrich
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2150
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Has thanked: 1 time
Been thanked: 2713 times
Contact:

Re: Blocking Filter In a Collimated Beam?

Post by christian viladrich »

No, I have not tested nor calculated it.

If I take the example of a SolarSpectrum or DayStar etalons, there is already a 5 to 10 A BF in the body of the filter
Adding a 4 A BF gives a little bit more contrast (see my test pages).

The real benefit is with the addition of a 1.5A filter. I also tested a 2 A filter which was good. Still the 1.5 A is better.

A 1 A would be still better. I have calculated it but no tested it. The price of the filter is rocketing ...

So I would say the best balance between performance / cost for stacking SolarSpectrum or DayStar etalons is with a 1.5A in a TEC.

If we go back to the Lunt / Coronado BF. Adding another 5 to 8 A BF would not change much the selectivity. Having or not a collimated / telecentric beam would not make a big change.


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
User avatar
DSobserver
Almost There...
Almost There...
Posts: 582
Joined: Sun Feb 19, 2012 2:36 pm
Location: FRANCE
Been thanked: 19 times

Re: Blocking Filter In a Collimated Beam?

Post by DSobserver »

I recently stack a coronado bf15 with a Lunt bf400:
Picture was very very dark


george9
Im an EXPERT!
Im an EXPERT!
Posts: 355
Joined: Tue Jan 26, 2016 1:28 am
Has thanked: 175 times
Been thanked: 426 times

Re: Blocking Filter In a Collimated Beam?

Post by george9 »

I put my Lunt 2A prominence filter (from an old Prom 15T blocking filter) in series with my Quark and with my Lunt LS80 SS. It gets darker for sure. It seems a little higher contrast, but hard to tell because darker can fool you and look like more contrast. In fact, I A-B tested the 2A versus an ND filter, and the effect was similar. So I have the 2A mounted in a standard 1.25" cell, but I never use it.

On the other hand, putting my Lunt DSII unit in series with either my Lunt LS80 SS or my Quark produces a great view, not as dim as the 2A and clearly higher contrast.

George


Post Reply