NEW direction in the solar narrowband imaging.

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Merlin66
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Thu Jun 28, 2018 12:21 am

A good SHG with large aperture and a good pixel/ chip sized camera would probably give you the results you're looking for.
The attached spreadsheet shows with a 900mm spectrograph and an 1200 grating an R>50000 could be achieved.
Theoretical bandwidth at 8542A around 0.09A; seeing at 2 arcsec would probably reduce this to 0.16A

Obviously increasing the grating l/mm to say 2400 l/mm would seem like a possible route to increased resolution, BUT the size of the grating (60 x 250mm!) and the required angle of incidence prevent this being used.
I think a 1800 l/mm (60 x 94mm if available?) could be made to work to give a R>100000 and a theoretical bandwidth of 0.05A

Bearing in mind as the bandwidth decreases, you need more and more aperture. Also you need a red sort filter when working above >7500A to suppress the 2nd order blue spectrum.
SimSpec SHG.xls
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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Thu Jun 28, 2018 12:46 am

Okay, i found it valery! This may confirm that the ir caii kline is indeed in the middle chromosphere like h-alpha. Howvere the ibis filter method is still not attainable by amateurs unfortunately. 1anstrom maybe enough to resolve something new and definitely a good place to start.

http://www.arcetri.astro.it/science/solare/IBIS/

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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Thu Jun 28, 2018 9:47 am

christian viladrich wrote:
Wed Jun 27, 2018 7:09 pm

An important point is missed in the discussion : the angular size of the fibrils. Just make the calculation ;-)
They are about the same as in H-a. See here http://www.arcetri.astro.it/science/solare/IBIS/

About a year ago I have communicated in length with Gianna Cauzzi (leading IBIS scientist) and she told me that fubrils in CaII I will be seen if we have 0,25A or better 0,2A bandwidth. With somewhat lower contrast they will be seen with 0,5A filter. But the best will be a double stacked 0,7 or 0,6A filters.

I see that Mark Wagner and Jen Winter are not willing to dive in this adventure with a new imaging filter.
May be there is a sense to ask Andy Lunt to make a small series of air-spaced and PT etalons for this wave length.
Should not be too expensive if we can create a pool of 10-12 customers.


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Last edited by Valery on Thu Jun 28, 2018 6:35 pm, edited 1 time in total.
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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Thu Jun 28, 2018 3:00 pm

christian viladrich has a model of something here with the coronado etalon, i do not know if it is real or just a theoretical idea

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

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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Thu Jun 28, 2018 3:01 pm

I think it may be entirely possible that the PST etalon and maybe all hydrogen alpha etalons broadcast this wavelength to an extent. It might be in our best interest to get the total transmission of a standard pst etalon.

I understand the coating maybe an issue, but if the etalon is already transmitting this wavelength at 80% i do not think the coating will make such a negative difference. I think pst etalon is a broadband transmission filter. So if we can prove this, then at that point we just need to make the blocking filters which should be a simple task.

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Re: NEW direction in the solar narrowband imaging.

Post by Spectral Joe » Thu Jun 28, 2018 3:54 pm

As has been pointed out, the 8542 line is similar in width to H alpha, unlike the UV CaII lines. Thus, bandpass requirements for an imaging system at this wavelength are similar to that at H alpha. The reflectivity of the coatings on the etalon plates is a major factor in determining the finesse of the etalon, the reflectivity needs to be high, higher than 90% and typically around 95%. For this, specialized multilayer coatings are used. It would be a fantastic coincidence if the coatings on a PST etalon had reflectivity that high at a wavelength far removed from the design wavelength. A purpose built etalon is needed if a non dispersive approach is the plan.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Thu Jun 28, 2018 6:34 pm

Spectral Joe wrote:
Thu Jun 28, 2018 3:54 pm
As has been pointed out, the 8542 line is similar in width to H alpha, unlike the UV CaII lines. Thus, bandpass requirements for an imaging system at this wavelength are similar to that at H alpha. The reflectivity of the coatings on the etalon plates is a major factor in determining the finesse of the etalon, the reflectivity needs to be high, higher than 90% and typically around 95%. For this, specialized multilayer coatings are used. It would be a fantastic coincidence if the coatings on a PST etalon had reflectivity that high at a wavelength far removed from the design wavelength. A purpose built etalon is needed if a non dispersive approach is the plan.
This is a first prohibiting factor. The second one is that if we can use the spacers from, say, LUNT LS35 or LS50 etalon, make new plates (not a problem at all) with special coating for 854nm (not a problem too) - it will be needed a very high or very low pressure (depends of spacers actual thickness) in the etalon vacuum chamber to come to the 8542,1A core.
Last edited by Valery on Fri Jun 29, 2018 5:25 am, edited 1 time in total.
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Re: NEW direction in the solar narrowband imaging.

Post by christian viladrich » Thu Jun 28, 2018 6:57 pm

Does anybody with a spectrograph can have a look at the transmission spikes of a Coronado etalon around 854 nm ?
It would be a marvellous coincidence if a transmision peak was right at 854.2 nm.
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Fri Jun 29, 2018 12:40 am

Christian,
I have access to a SM60 external etalon and a PST etalon and a hi-res Littrow spectrograph (R=10000).
I have previously looked at the transmission peaks but not in detail or at the nominated wavelength.
Let me see what I can do.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Fri Jun 29, 2018 5:29 am

Merlin66 wrote:
Fri Jun 29, 2018 12:40 am
Christian,
I have access to a SM60 external etalon and a PST etalon and a hi-res Littrow spectrograph (R=10000).
I have previously looked at the transmission peaks but not in detail or at the nominated wavelength.
Let me see what I can do.
Ken
Hi Ken,

Looking for good news! Keep fingers crossed.


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Re: NEW direction in the solar narrowband imaging.

Post by Montana » Fri Jun 29, 2018 7:08 am

Might be worth asking the new owner of Solarscope about the etalons, he seems very keen about any new ideas :)

Alexandra

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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Fri Jun 29, 2018 7:43 pm

Montana wrote:
Fri Jun 29, 2018 7:08 am
he seems very keen about any new ideas :)
More elaboration required!
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sat Jun 30, 2018 1:24 am

Looking at the solar spectrum map....
There seems to be an interesting CaII line at 8498.1A as well as the large shallow CaII 8542.2A.
If I ever see the Sun again I'll see how the etalons perform out in the NIR.
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sat Jun 30, 2018 2:41 am

Merlin66 wrote:
Sat Jun 30, 2018 1:24 am
Looking at the solar spectrum map....
There seems to be an interesting CaII line at 8498.1A as well as the large shallow CaII 8542.2A.
If I ever see the Sun again I'll see how the etalons perform out in the NIR.
Thanks, Ken, for the info. Can you, please, tell us how much less or more strong (wide, intensity) this line vs 8542,1A one?


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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sat Jun 30, 2018 2:57 am

Valery,
The attached screen from BASS2000 shows both lines.....
CaII_NIR.JPG
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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Sat Jun 30, 2018 3:11 am

If anyonehas a modifed pst, just remove the blocking filter and put an 850fs10 filter in front of the collimator. If you get an image it broadcasts the 850 specrtum. Simple test, itll cost like 100$ but will be worth it if it works for getting the image we are lookin for.

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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sat Jun 30, 2018 6:48 am

I've seen the etalon bands all the way down to the UV, but never paid attention to the NIR, I expect to see them all the way.
How close is one band to the required CWL I think will be the issue.
(OK, found an old spectrum of a PST etalon - low resolution and not focused for the NIR but the wavelength coverage is out to the >9000A.
This was taken with a Canon 1000D Fully modded. You can clearly see the etalon "comb" band passes. The broad absorption is the Telluric band(s) the prominent one at 7620A. You can see some absorption bands in the NIR but I need to do some calibration to define them.
Hopefully this at least shows the etalon does cove the NIR region.)
PST etalon_NIR.JPG
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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Sat Jun 30, 2018 7:50 am

Merlin66 wrote:
Sat Jun 30, 2018 6:48 am
I've seen the etalon bands all the way down to the UV, but never paid attention to the NIR, I expect to see them all the way.
How close is one band to the required CWL I think will be the issue.
(OK, found an old spectrum of a PST etalon - low resolution and not focused for the NIR but the wavelength coverage is out to the >9000A.
This was taken with a Canon 1000D Fully modded. You can clearly see the etalon "comb" band passes. The broad absorption is the Telluric band(s) the prominent one at 7620A. You can see some absorption bands in the NIR but I need to do some calibration to define them.
Hopefully this at least shows the etalon does cove the NIR region.)
PST etalon_NIR.JPG
Great job! You may have just bonked the solar imaging industry on its big fat head.... :bow2

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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sun Jul 01, 2018 12:51 am

Looking more closely at the Liege solar atlas, it appears we have the double CaII lines in the NIR - 8542A and 8662A.
I've done a rough calibration on the PST spectrum to show these lines.......
Liege_PST etalon_NIR_Ca II.JPG
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Sun Jul 01, 2018 3:57 am

Merlin66 wrote:
Sun Jul 01, 2018 12:51 am
Looking more closely at the Liege solar atlas, it appears we have the double CaII lines in the NIR - 8542A and 8662A.
I've done a rough calibration on the PST spectrum to show these lines.......
Ken,

Can you, please, tell us does the PST etalon has enough transmission at 8542,1A ?
Or it is worthless to consider it as a ready etalon for this line?


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Last edited by Valery on Sun Jul 01, 2018 4:53 pm, edited 1 time in total.
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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Sun Jul 01, 2018 4:27 am

Valery,
I’ll see what I can do.
An exposure of the NIR same camera, same exposure, with and without the etalon will be influenced by the etalon comb......let me think about it.
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Re: NEW direction in the solar narrowband imaging.

Post by marktownley » Sun Jul 01, 2018 10:15 am

Well i've just tried stacking my pst etalon on the Na Quark and made no improvement to anything with a dimmer image.
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Re: NEW direction in the solar narrowband imaging.

Post by TheSkyBurner » Tue Jul 03, 2018 1:42 am

marktownley wrote:
Sun Jul 01, 2018 10:15 am
Well i've just tried stacking my pst etalon on the Na Quark and made no improvement to anything with a dimmer image.
Did you keep the collimator attached?

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Re: NEW direction in the solar narrowband imaging.

Post by Merlin66 » Tue Jul 03, 2018 1:49 am

Guys,
Unless you can analyse the etalon comb/ CWL's in the "new" target wavelength - it's just a guess.....

I'm going to set up the spectrograph (R=10000) which should give at least 0.1A resolution and record the PST "comb" at the NIR CaII lines...if all goes well then I can try other lines......
If successful it still leaves the issue of finding a suitable blocking/ sort filter.......
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Re: NEW direction in the solar narrowband imaging.

Post by Valery » Tue Jul 03, 2018 3:49 pm

Thanks Ken for your support. Looking for the results of your PST etalon measurements!

Blocking filters are not a principal problem. Just a question of some money.


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