H-alpha SHG imaging from Sept 17

I LOVE finding out about different ways to appreciate the Sun and light in general. Use this forum to post your info or questions about various outside the mainstream ways to appreciate our life giving star!
Post Reply
thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

H-alpha SHG imaging from Sept 17

Post by thesmiths »

I haven't attempted any SHG imaging since the morning of the day I got on a plane LHR-YUL on Aug 11. The Sun is much lower now and the air much cooler. In the meantime, I upgraded my laptop (now 16GB RAM and a much faster CPU). I didn't actually notice any difference in the acquisition (the fps wasn't any higher -- seems to be camera limited). Our SHG reconstruction software seems to work fine on Windows 11; the faster CPU in the laptop finishes processing as quickly as my desktop now.

I added a 2-inch Astronomik L1 UV/IR filter around 15cm in front of the slit to act as a bit of an ERF. I saw no noticeable attenuation at H-alpha but possibly there is some at Ca-K. However, with the low Sun, I now have very little time to image in the morning before obstacles get in the way, so I could only take some H-alpha scans.

The colder air I think added to image stability; SHG is quite sensitive to any disturbances. However, there was some wind, which may have caused some slight shaking of the mount. The quality is a little lower than my attempts at the beginning of August, which had a string of very nice imaging days.

Below is a stack on the best 10 frames from a total of 20 scans (3 were discarded manually and I then let AS!3 do the rest). Some sharpening with ImPPG and levels adjustment with Photoshop Elements. The second image is a crop from the first image, inverted. The first one is best viewed by opening in a new tab. The second one is best viewed just by clicking on the image.

H-alpha SHG, 720mm focal length, 106mm aperture, 9 micron chrome on quartz slit, ZWO 183MM camera, 14x sidereal rate scan. 290 fps, 2.2ms exposure, gain zero. 17 Sept, 10:21 UTC to 10:27 UTC.
H-alpha SHG, 720mm focal length, 106mm aperture, 9 micron chrome on quartz slit, ZWO 183MM camera, 14x sidereal rate scan. 290 fps, 2.2ms exposure, gain zero. 17 Sept, 10:21 UTC to 10:27 UTC.
170922-8-Ha-720mm-106mm-2400g-14x-stack-10.jpg (1.26 MiB) Viewed 2318 times
H-alpha SHG, inverted.
H-alpha SHG, inverted.
170922-8-Ha-720mm-106mm-2400g-14x-stack-10-invert-crop.jpg (511.79 KiB) Viewed 2318 times
Last edited by thesmiths on Sun Sep 18, 2022 2:33 pm, edited 1 time in total.


thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

Here is some images created from an earlier set of scans, 20 scans from 09.23 UTC to 09:29 UTC. I had thought they were not as good as the ones above taken a little later. But after stacking (AS!3 chose 6 out of 20), the results were also quite good. I present the results here as an inverted full disk and a non-inverted cropped image.

H-alpha SHG, stack of 6 out of 20, inverted.
H-alpha SHG, stack of 6 out of 20, inverted.
170922-5-Ha-720mm-106mm-2400g-14x-stack-6.jpg (1.15 MiB) Viewed 2289 times
H-alpha SHG, cropped, non-inverted.
H-alpha SHG, cropped, non-inverted.
170922-5-Ha-720mm-106mm-2400g-14x-stack-6-crop.jpg (584.57 KiB) Viewed 2288 times
Last edited by thesmiths on Mon Sep 19, 2022 2:27 pm, edited 1 time in total.


User avatar
DeepSolar64
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 18728
Joined: Thu Sep 05, 2019 12:19 am
Location: Lowndesville S.C.
Has thanked: 17458 times
Been thanked: 16550 times

Re: H-alpha SHG imaging from Sept 17

Post by DeepSolar64 »

WoW, these are really good. I would think they are through an etalon equipped scope, not an SHG!!

James


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
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces

Image Visual Observer
" Way more fun to see it! "
User avatar
Bastelhannes
Ohhhhhh My!
Ohhhhhh My!
Posts: 154
Joined: Thu Jul 29, 2021 7:38 am
Has thanked: 83 times
Been thanked: 138 times

Re: H-alpha SHG imaging from Sept 17

Post by Bastelhannes »

I was looking through the posts, Douglas, but could not find the current setup...

Could you provide it a bit?


My greatest fear is being married alive.
christian viladrich
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2145
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Has thanked: 1 time
Been thanked: 2702 times
Contact:

Re: H-alpha SHG imaging from Sept 17

Post by christian viladrich »

Excellent Douglas !


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

Bastelhannes wrote: Sun Sep 18, 2022 10:37 am I was looking through the posts but could not find the current setup...
I looked through the posts and had trouble finding them myself! Here are the two posts that show the main outlines of the equipment:

Overview: viewtopic.php?t=37552

Under the covers: viewtopic.php?p=347782#p347782

There were two small changes made since the photos in the "under the covers" photos. One is I put a tilt corrector between the focuser extension tube and the slit. The issue with a long slit and a (fairly high) focal length is that if there is any tilt in the telescope optics, it is difficult to get focus across the slit from one end to the other. In any case, the focal plane is not entirely flat but has slight spherical curvature. But if there is also some tilt, it is even harder to get the focus right. It seems to be a not uncommon SHG problem for one side of the scan to be in focus but the other side to be slightly blurred.

The other minor change is I put an Asahi Pentax M42 helical focuser in front of the ZWO camera. I had previously used the bellows to focus the camera but I found the control was not fine and smooth enough. Now both the collimator and the camera can be very finely focused using helical type focusers. The adjustments needed for good focus are very minute (and of course change a bit with wavelength).

I'll mention a few more things while I'm at it. This is a somewhat scaled up version of the Solex design. The camera lens and collimator we use are both 135mm f3.5 lenses, so a diameter of 38.6mm. The Solex design is essentially 125mm f5, a diameter of 25.4mm. The grating in the Solex is 25mm square while I am using 50mm square. The Solex slit is only 4.5mm long but it's not clear whether the 1-inch optics of the Solex design can really achieve good quality across a slit that is much longer than that. The Solex is quite carefully designed so the standard components all work together. An analogy would be the difference in lenses required to image 35mm film vs 60mm film. I am able to image fairly successfully with a solar diameter of approximately 6.6mm in one go (using a slit that is 12mm long) but Solex users typically limit themselves to a solar diameter of 4.0mm or stitch together two (or more) such images to achieve a full disk at longer focal lengths (and greater apertures). If you want to stack SHG scans, the multiplying effect of having to do partial scans is quite an increase in imaging time (and storage space and processing time).

Another point I'll make about our setup is that it can only scan in DEC. But generally, I think most mounts will scan better in DEC than RA -- the moment of inertia is smaller (no counterweight) and the mount electronics is not busy also trying to track as well as to scan. Our setup is by default almost perfectly aligned in DEC so there is very little "tilt" in the scans and no adjustment is necessary to align the spectrometer perpendicular to the scan direction (a slightly finicky adjustment typically).


thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

DeepSolar64 wrote: Sun Sep 18, 2022 3:20 am I would think they are through an etalon equipped scope, not an SHG!!
You know, it is kind of amazing how far SHG imaging has come recently. As Christian Viladrich pointed out recently, it now sort of looks like triple stack etalon imaging. I contributed to Ken Harrison's book "Imaging Sunlight Using a Digital Spectroheliograph" which was published in May 2016 and the quality of the SHG imaging has improved so much since then.

If I were to try to identify the drivers for the recent improvement, I would point to the following technological advances:

1. Better cameras. Larger sensor size; smaller pixels; faster interfaces, leading to high capture rates of high-resolution, high-bit-depth video files.

2. Improved slits. Lithographically formed slits are much more uniform, greatly eliminating imaging defects.

3. Much improved software. The INTI software originally written by Valerie Desnoux and added to by others has dramatically improved the quality and throughput of the image reconstruction process. Improvements in capture software (FireCapture and SharpCap) I think have also been important because of the increase in acquisition rates.

4. Better computers. More DRAM, faster CPUs, NVMe SSDs, USB 3.0 and USB-C has allowed fast acquisition and storage of large amount of data. The processing time for an image reconstruction has dramatically decreased as well.

5. The ability to stack multiple SHG scans. Back in 2016 the idea of SHG stacking seemed out of reach, almost absurd, I would say. Now it is relatively common due to all the advances listed above. Where would etalon imaging be if not for the ability to stack frames and therefore digitally sharpen?


User avatar
Bastelhannes
Ohhhhhh My!
Ohhhhhh My!
Posts: 154
Joined: Thu Jul 29, 2021 7:38 am
Has thanked: 83 times
Been thanked: 138 times

Re: H-alpha SHG imaging from Sept 17

Post by Bastelhannes »

thesmiths wrote: Sun Sep 18, 2022 2:27 pm
Another point I'll make about our setup is that it can only scan in DEC. But generally, I think most mounts will scan better in DEC than RA -- the moment of inertia is smaller (no counterweight) and the mount electronics is not busy also trying to track as well as to scan. Our setup is by default almost perfectly aligned in DEC so there is very little "tilt" in the scans and no adjustment is necessary to align the spectrometer perpendicular to the scan direction (a slightly finicky adjustment typically).
Great, thank you Douglas. And now I am thinking about building a bigger Sol'ex. Grump. It is even more addictive than cocaine...

One question arrived some time ago and I asked it already, but never got an answer:
How should we scan? You scan in DEC, some in RA. I am the lazy guy: I just turn off the tracking and let the sun move itself. What are the advantages and disadvantages?

Karsten


My greatest fear is being married alive.
thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

Bastelhannes wrote: Sun Sep 18, 2022 4:46 pm How should we scan? You scan in DEC, some in RA. I am the lazy guy: I just turn off the tracking and let the sun move itself. What are the advantages and disadvantages?
In my opinion, "drift scanning" is good in the sense that the scan speed will be highly regular, but the problem is all the data is pushed down in frequency. It is a good assumption that most sorts of noise in nature have a 1/f frequency distribution. Thus noise will be greater at lower frequencies so it is always a good idea to push the data to higher frequencies. This means scanning at as fast a rate as practical will reduce ambient noise in the images.

With regards to RA vs DEC scanning: I mention above why I think mounts might work better for DEC than RA. This is certainly true for lighter weight mounts (e.g. EQ5) but may not be so true of heavier and better mounts (e.g. EQ6). If to do partial scans (by that I mean not full disks), then I think RA scans have some advantages because most solar features tend to occur along equatorial bands. So a partial scan done parallel to the solar equator will capture all the features along the band. This will also make creating a mosaic much easier, I have found. For full disk scans, this is less obviously an advantage, except that typically is not so easy to get both ends of the slit in good focus. It is generally the case that images will look better if the north or south pole is a bit out of focus than if the east or west limb of the Sun is blurred.


User avatar
Montana
Librarian
Librarian
Posts: 34526
Joined: Mon Oct 17, 2011 5:25 pm
Location: Cheshire, UK
Has thanked: 17521 times
Been thanked: 8763 times

Re: H-alpha SHG imaging from Sept 17

Post by Montana »

Wow!! these are crazy beautiful :bow :hamster:

Alexandra


thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

With regards to the 2-inch Astronomik L1 UV/IR filter that I recently installed: I have the impression that the data at the camera was a little cleaner than previously and was therefore easier to focus. This might be because before there was a lot of IR light bouncing around inside and the CMOS cameras are of course quite sensitive in the infrared.

Moreover, the transmission of chrome increases at longer wavelengths so the slit will actually let increasing amounts of stray light through unless there is a cut-off filter.

Transmission of chrome layer with wavelength
Transmission of chrome layer with wavelength
chrome OD5.JPG (40.54 KiB) Viewed 2206 times


User avatar
marktownley
Librarian
Librarian
Posts: 42120
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20229 times
Been thanked: 10111 times
Contact:

Re: H-alpha SHG imaging from Sept 17

Post by marktownley »

Exceptional images there Douglas!


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
fulvio.mete
Ohhhhhh My!
Ohhhhhh My!
Posts: 116
Joined: Tue May 20, 2014 8:59 am
Location: Rome, Italy
Been thanked: 84 times
Contact:

Re: H-alpha SHG imaging from Sept 17

Post by fulvio.mete »

Excellent images, Douglas, with an intelligent setup.
About the scans, I'm not sure that the Dec scans are better of AR scans .In my case, that use only the natural flow of sundisk along the slit, AR scans are surely better ,as you stated, in capturing equatorial data.
About the IR cut filter in CMOS Cameras, surely it could make a noticeable difference, for these are much sensitive to IR radiation.I own a ZWO 290 MC, and the use of IR cut make a BIG difference in the output images.


thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

fulvio.mete wrote: Tue Sep 20, 2022 3:43 pm I own a ZWO 290 MC, and the use of IR cut make a BIG difference in the output images.
Do you mean when using in one of your spectroscopy instruments? Or for another application?


User avatar
Bastelhannes
Ohhhhhh My!
Ohhhhhh My!
Posts: 154
Joined: Thu Jul 29, 2021 7:38 am
Has thanked: 83 times
Been thanked: 138 times

Re: H-alpha SHG imaging from Sept 17

Post by Bastelhannes »

fulvio.mete wrote: Tue Sep 20, 2022 3:43 pm About the IR cut filter in CMOS Cameras, surely it could make a noticeable difference, for these are much sensitive to IR radiation.I own a ZWO 290 MC, and the use of IR cut make a BIG difference in the output images.
I am confused:
1. We are using a grating to select specific wavelengths. The ones not wanted go aside the sensor. An IR cut filter does not make any sense to me due to this physical behavior.
2. I want to take pictures at 850 nm. I am not sure, if an IR cut filter prohibits this (I do not know the edge/threshold wavelength of the filter.

Due to my brain damage I am not sure, if I am correct. I figured out my brain created some weird alternative facts, which are totally wrong but seem real... I can really recommend COVID vacs to create a new impression of life.. sigh...


My greatest fear is being married alive.
thesmiths
Almost There...
Almost There...
Posts: 1053
Joined: Mon Jun 04, 2012 8:13 pm
Location: London, England
Has thanked: 42 times
Been thanked: 1485 times

Re: H-alpha SHG imaging from Sept 17

Post by thesmiths »

Bastelhannes wrote: Sat Sep 24, 2022 10:05 am I am confused:
1. We are using a grating to select specific wavelengths. The ones not wanted go aside the sensor. An IR cut filter does not make any sense to me due to this physical behavior.
2. I want to take pictures at 850 nm. I am not sure, if an IR cut filter prohibits this (I do not know the edge/threshold wavelength of the filter.
1. It turns out there can be a lot of scattered light which does not bounce off the grating so therefore is not selected. Or light of the wrong wavelength from the grating reflects off the walls and into the camera. It is not uncommon to, for example, put an H-alpha filter in front of the camera for this reason. But then you need to remove it or change it to look at a different wavelength, such as H-beta or violet.

2. For 850nm, you could put an IR pass filter (common for planetary imaging) onto the camera. This would increase the contrast.


User avatar
Bastelhannes
Ohhhhhh My!
Ohhhhhh My!
Posts: 154
Joined: Thu Jul 29, 2021 7:38 am
Has thanked: 83 times
Been thanked: 138 times

Re: H-alpha SHG imaging from Sept 17

Post by Bastelhannes »

And I thought using the IMX462, which is very sensitive at 850 nm...

Okay, i am going to try....


My greatest fear is being married alive.
Post Reply