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Old 18-09-2019, 07:52 AM
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Merlin66 (Ken)
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New Solar CaK filter assembly

Just completing a new CaK 2A filter assembly.....
This version is based on a 2" Baader Blue CCD filter as an "ERF" give a good UV cut below CaK (393nm) and above about 520nm.
Then follows a #1 "Yellow" filter removed from a CaK PST. This has a bandwidth of 2A centred on CaK.
The third element is an Omega 2A CaK filter (as a double stack)

The initial results look promising...
bright speckles show the narrow bandwidth!

I need to consider whether or not at add a tilter to each or either of the 2A filters to fine tune the CWL.
Used with a stopped down ED80 (60mm f10) and ASI 1600MM.
Firecapture, AS3!, ImPPG, Corono
Onwards and Upwards.
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Old 18-09-2019, 08:11 AM
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h0ughy (David)
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Awesome results. Would you use a tilter like the zwo one?
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Old 18-09-2019, 08:43 AM
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Merlin66 (Ken)
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David,
Thanks!

The ZWO tilter is ideal for removing Newton Rings but not for dynamic narrow band filter tilting.
I'm lucky enough to have a couple of SkyBender filter tilters. These units allow a full degree of freedom and are pretty repeatable.
To be honest, it really needs the spectrograph, with resolution around 0.05A to accurately determine the CWL and and bandwidth.
The differences between H alpha and CaK are shown below.
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Old 19-11-2019, 08:45 AM
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Merlin66 (Ken)
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If the weather improves (!!) I'd like to get some CaK images of the current AR 2752....
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Old 19-11-2019, 09:43 AM
Saturnine (Jeff)
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Watching and reading with interest but no intention of going down that path. Just admiration of your skills and dedication Ken.
Some very recent photos on Spaceweather. com of the current active region AR2752, with a minor flare, as I'm sure you're probably aware of already.
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Old 19-11-2019, 10:35 AM
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Merlin66 (Ken)
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Thanks, Jeff.
Just need to design and build a solar scope which can penetrate clouds
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Old 19-11-2019, 10:59 AM
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Quote:
Originally Posted by Merlin66 View Post
Thanks, Jeff.
Just need to design and build a solar scope which can penetrate clouds
And smoke. So we don't have a featureless Sol anymore
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Old 19-11-2019, 01:00 PM
Saturnine (Jeff)
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Just had the Solar scope out an hour ago, very sunny clear skies but some smoke haze of course. Didn't bother trying to image but visually the active area was a tiny dark spot with no hint of any bright flares etc. but there was 1 large prom on the NW ! limb, faint but seemingly detached from the chromospere.
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Old 11-12-2019, 09:27 AM
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Hi ken, I was thinking about how to maximise contrast of solar granulation and was thinking about how the blackbody radiation might be different across each granule.

I plotted the blackbody radiation curves for 5500k and 4500k ( assuming these values are representative of the centre and esge of each granulation) as well as the ratio between the two as a function of wavelength.

It looks to me that the biggest ratio and therefore contrast for contiuum would be at the shortest wavelengths. But recommendations in solar observing literature is for an orange filter to improve seeing ( less refraction) or green ( eg the baader solar continuum filter to be used with baader solar safe film.).

I guess my simple model needs an additional term for the amount of atmospheric scattering as a function of wavelength.

Any thoughts?

Cheers, Hamish
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Old 11-12-2019, 10:04 AM
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Merlin66 (Ken)
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Hamish,
The "Bible" on granulation is Bray, Loughhead and Durrant's "The Solar granulation", CUP, 1984.

They determine seeing conditions are the major factor (surprise, surprise!)
On page 46, they present a table showing the measured contrast granulation to inter-granulation lanes:
Wavelength (nm) Contrast (%)
530 16
595 23
550 21-27
465 36

It would appear any filter which picks up on the continuum around 465-595nm would give best results.

Ken
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Old 11-12-2019, 10:24 AM
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Thanks ken. The shortest band of those figures seem to give highest contrast. Did they list anything shorter?
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Old 11-12-2019, 03:30 PM
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Merlin66 (Ken)
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Hamish,
there is an entry for 461nm , contrast 20%.
Ken
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Old 11-12-2019, 09:19 PM
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thanks! (and apologies for the slight deviation from topic.)


I managed to find a pdf of bray and loughhead solar granulation but it was the 1967 edition and they were not confident to say much about contrast of the granulation at that time as there had been no spaceborne instruments and only a couple of balloon-borne telescopes.


I did find a paper by bray "the wavelength variation of granule/intergranule contrast" in solar physics vol 77 (1982) pp 299-302. it does have some nice discussion and derivation of delta T value between the bright and dark bits of the granulation but it appears that instrumentation was still a bit lacking.


I wonder if much useful data was gained by the apollo telescope mount on skylab. As a first long duration spaceborne solar telescope, and seeing now that the state of the art in solar observation at the time was limited by the available seeing, it would seem it might have been potentially a big step up at the time.
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