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Comparing 0.3A and 0.6 A bandpass in Ha

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Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Thu Jul 07, 2016 6:57 pm

Dear all,
I had some fun with the following test comparing 0.3 and 0.6A Ha filters.
Here is a first comparison with the same processing applied to both images. There is no local processing. Only linear visualisation with the objective of having about the same luminosity on the disk.
The 0.3 A filter is on the left and the 0.6 A on the right :
Image

In the 0.6A image, the photosphere is visible through the chromosphere. This is why the contrast is lower.
The intensity of the chromospheric fringe is about 33% the intensity of the disk with the 0.6A, versus 46% with the 0.3A filter.

Here, I processed each of the image in order to get the most of each:
Image
The granulation of the photosphere is clearly visible through the chromosphere in the image with the 0.6A.
For some strange reasons, the chromospheric fringe looks sharper with the 0.3A.Something related to the Doppler effect ?
The prominence is also more visible with the 0.3A, but this is just because of its evolution between these two images.

Here are the full images :
Image
Image
Cheers
Christian
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Bob Yoesle » Fri Jul 08, 2016 2:42 am

Nice comparison Christian!

Since no "fringe" is visible when double stacking 0.7 A bandpass filters (even though the FWHM becomes ~ 0.5 A) the real-world performance of such a DS'd filter system appears to exceed that of a 0.3 A single filter: http://www.cloudynights.com/topic/43800 ... ted-equal/
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by mattwastell » Fri Jul 08, 2016 9:22 am

Thanks for the comparisons. The images are great BTW!
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Montana » Fri Jul 08, 2016 9:23 am

I always find that prominences are more visible with a lower band pass.

I guessed immediately it was a rear mounted etalon as the photosphere is still visible in the 0.3A due to the leakage of the broad shoulders in the transmission curve.

Great shots though :hamster: :bow :bow

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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by cshahar » Fri Jul 08, 2016 3:25 pm

Christian, this is very informative. Thank you!

-Charles

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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Valery » Sat Jul 09, 2016 12:00 pm

Thanks, Christian. Very interesting comparision between two DayStar etalons.

BTW Have you applied a flat field to both etalons? Or none of them?
How much better in uniformity the PE vs SE versions?

Can you show 2-3 images taken with DayStar Ion 0,3A SE without flat field applied?

Thanks in advance.


Valery.


BTW, I have conducted much more numerous comparisions between two DayStar etalons
with 0,25A (RMS) and 0,38A (RMS) etalons and the difference is not as prominent as 0,3A vs 0,6A
but still clearly visible.
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by george9 » Sat Jul 09, 2016 12:36 pm

Very useful for someone choosing a filter, especially the first two images. For someone purely visual, given the difference in price, it is not clear that you get that much by halving the bandwidth. I was thinking 0.5A would about right, all things considered. The eye has a good dynamic range, so the brighter photosphere in the .6 compared to the .3 is not as harmful as it would be for an image. If you really want to increase visual contrast significantly, you've just got to figure out some way to double stack.

I understand the theory that with a narrow filter, Doppler effects could filter out parts of prominences and spicules, but in practice, I just have not seen it (other than filaments that are way off band). I think the main effect is not bandwidth but brightness. If the narrower filter (single or double stack) has a lower peak transmission, then you'll definitely lose prominences and spicules. And if you can boost brightness, e.g., by dropping one of two ERFs for double stack, then prominences and spicules will be just as good as in a wider filter. (I am sure there are exceptions to this, when some feature does have a large Doppler effect, but it just doesn't seem common.)

Christian, did it seem that the brightness of the proms and spicules in the 0.6 and 0.3 were identical before processing? That is, my understanding is that you normalized the first two images so that the disks (photosphere + chromosphere) looked the same, which made the proms in the 0.6 look dimmer. But before processing, did the .6 and .3 let about the same amount of chromospheric light through? Or perhaps was the .3 dimmer than the .6?

George


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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by marktownley » Sun Jul 10, 2016 11:06 am

A very informative comparison Christian, thanks :)
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Sun Jul 10, 2016 9:01 pm

Thanks a lot for your comments :-)

Bob : Yes, FWHM is only part of the story. Double stacked filters take the lead because of the reduction of the continuum contribution.

Alexandra : all other things being equal, there should not be any difference between a front and a rear mounted filter. The wings have the same width for mica-spaced of air-spaced etalons of a given FWHM. Difference can come from the BF, and of course between DS and SS. Another thing may be the difference between advertised and actual FWHM.

Valery : yes, I applied flat image for both the PE 0.6 and Ion 0.3A. The PE is rather uniform, while part of the Ion is a little bit off-band. I' ll post the flat images soon.
What type of Daystar etalons did you test ? PE, SE, Ion ?

Georges : I agree with you. I have not kept the raw images, but I kind of remember the 0.3A is about 2 to 3X darker on prominences (with same exposure time). I am not 100% sure. I have to check it again ... I think (just as you do) this is more an issue related to the difference of peak transmission in the BF and the polarising filters, rather than a question of band pass.
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by mdwmark » Mon Jul 11, 2016 6:55 am

Hi Christian,
I liked your images. But they where all in the red wing. They are good examples of what .3-.5Ang red looks like. When you see the tips of the surface detail with the higher contrast. Then you know you are past the center line. It will look softer when you are in the center of the line.
Also, if you where at F/30, then you where not at .3Ang HW. You would really need to be around F/45 to take advantage of the narrower HW. The .6 at F/30 would show less effect of boarding then the narrower filter.(it looked like you where using the F/27 system, if I read the image right. Then the .3HW would be closer to .6Ang and the .6 would be closer to .8Ang)
Just a friendly comment
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Valery » Mon Jul 11, 2016 6:24 pm

christian viladrich wrote:
Valery :
What type of Daystar etalons did you test ? PE, SE, Ion ?
Christian,

These are two Quarks Chromosphere - one with a 0,38A (RMS) and the second is 0,25A RMS.


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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Valery » Mon Jul 11, 2016 6:28 pm

mdwmark wrote: if I read the image right. Then the .3HW would be closer to .6Ang and the .6 would be closer to .8Ang)
Just a friendly comment
Mark W.
Hi Mark,

Do you have some photos taken with your narrowest filters (say, 0,2A or even narrower) and at slow enough F/D to show
all the advantages of these narrow filters?

The most contrast images I ever saw (except professionals) were taken through DS 0,3A etalons.

Thanks in advance.


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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Mon Jul 11, 2016 6:49 pm

Hello Mark, thanks a lot for having had a look there :D

I've made some calculations about the impact of the F/D ratio on the actual bandpass for mica-spaced F-P. I've got a curve which is a bit different than the one provided by Daystar :
Image
I was wondering if you could have a quick look at some of the calculations there. I know it is OK for air-spaced F-P since I've reached the same results as for a space mission project. But maybe I've got it wrong somewhere for the mica-spaced F-P:
http://www.astrosurf.com/viladrich/astr ... lar/FP.htm

I've tested various positions (to the red and blue) with the PE and the Ion filters. That ones were giving the darkest images, so possibily at the center of the Ha line ?

Ghost : I've made some comments/ questions to your post.
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Mon Jul 11, 2016 7:45 pm

Valery : Thanks, this is very interesting. How did you measured the FWHM ? Do you have some kind of spectrometer ? If so, did you find a large (or small) variability between the different Quark you have tested ?

I have also have this set of comparison images taken recently with the C8 Edge-HD at F/27.
Daystar PE 0.6 A on left, Ion 0.3A on right. The processing and visualisation thresholds are exactly the same for for images :
Image
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by marktownley » Mon Jul 11, 2016 8:00 pm

christian viladrich wrote:Valery : Thanks, this is very interesting. How did you measured the FWHM ? Do you have some kind of spectrometer ? If so, did you find a large (or small) variability between the different Quark you have tested ?

I have also have this set of comparison images taken recently with the C8 Edge-HD at F/27.
Daystar PE 0.6 A on left, Ion 0.3A on right. The processing and visualisation thresholds are exactly the same for for images :
Image
You can see the granulation hiding very well in the image on the left! :)
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Mon Jul 11, 2016 9:20 pm

Yes, it is clearly there Mark ;-)
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by jp-brahic » Tue Jul 12, 2016 7:31 am

PE 0.6 have a big problem :) I saw exactly the same thing on another PE 0.6

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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Derek Klepp » Tue Jul 12, 2016 8:18 am

Very informative thanks.

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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by george9 » Tue Jul 12, 2016 11:05 am

Yes, looking at those latter images, you may have convinced me about the 0.3A. I.e., that if you are going single stacked, then it is probably worth the money for the 0.3A. Certainly for imaging. For visual, I would have to compare 0.5A to 0.3A to make sure the 0.3A was not too dim visually. I know a 0.25A (I think) Solarspectrum filter at NEAF is certainly bright enough every year.

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Last edited by george9 on Tue Jul 12, 2016 8:40 pm, edited 1 time in total.

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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by eroel » Tue Jul 12, 2016 2:51 pm

Chris.
A very interesting theme, thanks for sharing it.
Regards,
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by marktownley » Wed Jul 13, 2016 5:33 am

That Ion would work well with a PST etalon behind it. Lots of contrast then! ;)
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by marktownley » Wed Jul 13, 2016 10:29 am

I thought I might throw this into the mix as serves as comparison for some of the focus of the discussion that has evolved.

The following shot was taken with my HaT and a Quark that was quoted as being 0.4a that has been double stacked with a PST etalon. Notice lack of continuum leakage due to wings being cut.

Images5353-ha-bw by Mark Townley, on Flickr
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by christian viladrich » Thu Jul 14, 2016 9:00 am

Very interesting Mark !
Could you post of the sun an image with / without the PST double stack ? And an other of the set up ?
Thanks !
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Re: Comparing 0.3A and 0.6 A bandpass in Ha

Post by Valery » Thu Jul 14, 2016 7:40 pm

jp-brahic wrote:PE 0.6 have a big problem :) I saw exactly the same thing on another PE 0.6

jp
I am sure there is no any problem with a DayStar 0,6A PE. They just too wide and hence a lower contrast.
0,3A is MUCH narrower and contrasty!


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