Spectroscopy measure of Omega/PST CaK filter

this is the main message area for anything solar :)
Post Reply
User avatar
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Sun Sep 13, 2020 1:31 am

Between cloud....
I'm in the process of measuring the bandwidth and central wavelength of the DIY CaK filter I use.
Based on the images I've uploaded previously, any bets on the outcome????
111932c_full.jpg
111932c_full.jpg (663.5 KiB) Viewed 257 times


"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
DeepSolar64
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2790
Joined: Thu Sep 05, 2019 12:19 am
Location: Edneyville North Carolina U.S.A.
Has thanked: 1051 times
Been thanked: 1175 times

Re: Spectroscopy measure of Omega/PST CaK filter

Post by DeepSolar64 » Sun Sep 13, 2020 2:39 am

This looks really nice! Is making a CaK filter cheaper than buying one? Who do you buy the filter elements from? Baader?


Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Traq 60mm with Baader AstroSolar film
Lunt, Coronado, TeleVue, Orion, Celestron and Sears eyepieces

Image Visual Observer
" Way more fun to see it! "

User avatar
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Sun Sep 13, 2020 3:00 am

Three Omega Bob filters (yes, I know some users say they are rubbish quality!), a Baader Blue CCD filter as an upfront erf and fitted with the #1 "yellow" filter from a PST Cak scope.
Certainly not cheap!!!
I think the Lunt CaK filter is probably more cost effective, but.....I think the DIY has a tighter bandwidth....wait till the results are in.


"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: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Sun Sep 13, 2020 6:36 am

Limited test...
The only available spectrograph was a Spectra-L200 with a 1200 l/mm grating, this gave a dispersion of 0.23A
Using the normal set up with the ED80 stopped down to f10.

The bandwidth of the DIY filter is very close to 1.0 A
Bad news: due to the filter assembly "sagging" due to the added weight of the spectrograph the filter CWL was shifted towards the blue wing of the CaK line. Gaffa tape was used to "support" the spectrograph which was not successful, but at least demonstrated the effect of tilt on the CWL....it moved towards the centre of the CaK line. I can only assume at the moment that if it was properly supported and aligned to the optical axis, that the filter would be "on band" at CaK.

I need to rig up a rigid support for the spectrograph to obtain quality results. In the meantime I'm comforted by the fact the bandwidth is pretty good!
Onwards and Upwards.
Cak filter test 130920.png
Cak filter test 130920.png (60.39 KiB) Viewed 241 times


"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
marktownley
Librarian
Librarian
Posts: 29097
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 1981 times
Been thanked: 766 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by marktownley » Sun Sep 13, 2020 7:15 am

Nice analysis Ken!


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
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Sun Sep 13, 2020 8:32 am

Just checked the Lunt CaK filter the 18mm is over $1000 and rated for 2.4 A (or less???)


"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
Montana
Librarian
Librarian
Posts: 23595
Joined: Mon Oct 17, 2011 5:25 pm
Location: Cheshire, UK
Has thanked: 2098 times
Been thanked: 728 times

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Montana » Sun Sep 13, 2020 11:16 am

Wow!! lovely work Ken, I wish you could come and test all my filters :)

This is very interesting indeed.

Alexandra




LTHB
Im an EXPERT!
Im an EXPERT!
Posts: 235
Joined: Thu Mar 03, 2016 7:31 pm
Been thanked: 165 times

Re: Spectroscopy measure of Omega/PST CaK filter

Post by LTHB » Sun Sep 13, 2020 8:35 pm

Really interesting, Ken!

Can you explain the marvelous FWHM of 1A? I think the Coronado filter should have 2.2A and the OmegaBob filters are advertised as 2A, but my copy is way above that (according to the transmission curve that came with the filter). Did you tilt the filters or is the low FWHM the effect of "simple" stacking?

Frank



User avatar
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Sun Sep 13, 2020 11:53 pm

Frank,
The combination of the cut-off wavelengths and "double stacking" contributes to the reduced bandwidth.
The tilt (sag of the filter assembly) moved the central wavelength (CWL) towards the blue.


"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
eroel
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 6141
Joined: Mon Dec 19, 2011 10:45 pm
Location: México D.F.
Been thanked: 744 times

Re: Spectroscopy measure of Omega/PST CaK filter

Post by eroel » Mon Sep 14, 2020 2:35 am

Ken:
Very interesting thread.
Thanks for sharing it.
Best regards,
Eric.



User avatar
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Mon Sep 14, 2020 3:30 am

Thanks everyone for the comments/ feedback.
Using the spectrograph to measure filters/ etalons etc. removes the subjectiveness of assessing the capabilities of your filter(s).

My usual spectrograph (R=10000) is locked up on the C11 for ProAm work at the moment.
Bit difficult at the moment, but if I can assist in the future with any spectrographic measurements I'd love to help.
(There may be a spectroscopist in your area who could help - local astronomy/ science group??)


"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

AndiesHandyHandies
Im an EXPERT!
Im an EXPERT!
Posts: 317
Joined: Fri Mar 30, 2018 6:46 am
Location: Derbyshire UK
Has thanked: 266 times
Been thanked: 135 times

Re: Spectroscopy measure of Omega/PST CaK filter

Post by AndiesHandyHandies » Mon Sep 14, 2020 9:12 am

Hi Ken,

Are the two CAK filters in the little box with the corresponding coloured peaks two different CAK set ups?

Are you using three filters? Rather than 3 Omega filters and the other two the wording implies?

Andrew.



User avatar
Merlin66
Librarian
Librarian
Posts: 3588
Joined: Tue Dec 13, 2011 1:23 pm
Location: St Leonards, Australia
Has thanked: 7 times
Been thanked: 48 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by Merlin66 » Mon Sep 14, 2020 10:21 am

Andrew,
The two profiles show the bandwidth shift when the filter assembly was slightly moved.
It’s the same filter, just different tilts.


"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
marktownley
Librarian
Librarian
Posts: 29097
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 1981 times
Been thanked: 766 times
Contact:

Re: Spectroscopy measure of Omega/PST CaK filter

Post by marktownley » Mon Sep 14, 2020 11:10 am

You seem to have got lucky with that Omega filter Ken, sadly something I never managed...


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!

Post Reply