Improved H-alpha SHG high-resolution imaging from morning of 11 July

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

Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by thesmiths »

With some hot sunny weather in London, we've been able to keep practicing and trying to improve our SHG imaging efforts. Versus the last run viewtopic.php?t=36970, we attempted to get a more even illumination of our SHG optics. This required taking out the scalpel and hot glue gun to do some foamboard surgery. For those who have followed our SHG efforts, our main instrument is conceptually like the SolEx http://www.astrosurf.com/solex/sol-ex-c ... on-en.html but built from foamboard and hot glue, rather than 3D-printed PETG.

Foamboard SHG with the top cover removed. 100mm f4 collimator (Pentax bellows lens, M42 mount) with Pentax helicoid focuser on the outside. 100mm f4 Galaxy SLR camera lens (with integrated helical focuser), C-mount. 30mm x 30mm 2400 l/mm holographic grating (Edmund Optics). ZWO 183MM camera. 9 micron wide lithographic chrome on fused quartz slit, 12mm long.
Foamboard SHG with the top cover removed. 100mm f4 collimator (Pentax bellows lens, M42 mount) with Pentax helicoid focuser on the outside. 100mm f4 Galaxy SLR camera lens (with integrated helical focuser), C-mount. 30mm x 30mm 2400 l/mm holographic grating (Edmund Optics). ZWO 183MM camera. 9 micron wide lithographic chrome on fused quartz slit, 12mm long.
1424.jpg (327.5 KiB) Viewed 1176 times

When we originally built our device, it was designed to use a 3mm long Thorlabs slit. Since upgrading to a 12mm long lithographic slit, the small alignment errors of the collimator lens versus the camera lens were much more noticeable. We performed the surgery and inserted some small cardboard shims to correct the misalignment (by slightly raising the front of the camera lens and slightly raising the back of the collimator lens).

As a result, we were able to get much more even illumination across the long slit. The focus across the slit was also improved slightly but it was still difficult to bring the whole length into good focus at the same time. Below is a good image taken with a kind of "average focus" across as much of the solar disk as possible. The image is quite large (the video file was 3300 pixels wide) so best to see the image at full resolution by opening in a new tab.

H-alpha full disk SHG. 700mm FL, 106mm aperture, APO triplet. 10 best SHG images stacked of 26. Imppg, Photoshop.
H-alpha full disk SHG. 700mm FL, 106mm aperture, APO triplet. 10 best SHG images stacked of 26. Imppg, Photoshop.
110722-Ha-stack-10-26.jpg (1.58 MiB) Viewed 1176 times
I think there was a mount balancing problem (one I had never seen before) so a lot of images scanned in one direction I had to toss out. In the end, I found 26 images of good quality and told AS3! to stack the best 10. For comparison, here is an image from Arne Danielsen taken a few hours later on the same day with a Coronado 60mm: https://www.astrobin.com/full/5buv9r/

I played with the focus a bit and managed to improve the focus on the big feature in the top half (AR3053). Again there were mount problems so I could only find 19 good images to stack and asked AS3! to stack the best 5.

H-alpha SHG: close up of AR3053, 100% crop. Best 5 of 19 SHG images stacked. Imppg, Photoshop.
H-alpha SHG: close up of AR3053, 100% crop. Best 5 of 19 SHG images stacked. Imppg, Photoshop.
110722-Ha-stack-5-19-crop.jpg (520.82 KiB) Viewed 1176 times

Unfortunately, I did not try to readjust the focus again to try to bring the bottom actively area into better focus (AR3055). Nevertheless, I made a 100% crop from the full disk image above and applied a bit more unsharp mask to bring out the details.

H-alpha SHG: close up of AR3053, 100% crop of the full disk image.
H-alpha SHG: close up of AR3053, 100% crop of the full disk image.
110722-Ha-stack-10-26-crop.jpg (416.66 KiB) Viewed 1176 times
Last edited by thesmiths on Mon Jul 11, 2022 10:50 pm, edited 1 time in total.


User avatar
hopskipson
Im an EXPERT!
Im an EXPERT!
Posts: 328
Joined: Sun Jan 13, 2019 9:27 pm
Location: Queens, NY
Has thanked: 404 times
Been thanked: 191 times

Re: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by hopskipson »

Wow those are some nice images! I’m just trying to figure out how to put the Sol’Ex together but images like these are an incentive to get it done.


James
These pretzels are making me thirsty! (C.C.)
The Quark introduced me to this wonderful side of the hobby and the sun hasn’t disappointed yet.
Solar Equipment: Solar Spectrum RG-18 0.3A, Coronado Solarmax 90mm etalon Isle of Man SN-001, Tuscon SN-380 and Meade SM2, Lunt LS80 DS, Quark Chromosphere, Lunt 2" wedge, 2-Lunt CaK II 1200, Baader 3.8 and 5.0 solar film in 208mm cells, and 3D printed Sol'Ex SHG, Lunt 40mm
Coming Soon: Solar Spectrum CaK II <1A filter
Sergio Alessandrelli
Im an EXPERT!
Im an EXPERT!
Posts: 208
Joined: Fri Mar 15, 2019 5:02 pm
Has thanked: 883 times
Been thanked: 548 times

Re: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by Sergio Alessandrelli »

Wow! Really interesting imaging thecnic.


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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by Montana »

:bow :bow :bow these images get better and better, I am just blown away by the quality :bow I take my hat off and salute you

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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by thesmiths »

Just to help people understand how the images were created, I also show a screenshot of the FireCapture and EqMod applications while in use. The image signal is in the fine lines of the curved H-alpha line. You can see that the left side shows sharper focus than the right side, demonstrating that it was difficult to achieve good focus across the whole solar disk. The brightness of the two sides is quite well balanced, however.

The exposure was set to 1ms (which is quite fast) and means that the fps was set by the USB traffic speed (which had to be set to no higher than 75% to avoid "lost frames"). The gain setting was used to control the brightness of the image and of course should be set to as low as feasible. The brightness of this image is about what it should be for optimal imaging: there are fine lines visible within the H-alpha spectral line but nothing in the line looks saturated. It does not matter if the data outside the spectral line is saturated.

Acquisition of an image involves the following steps: (1) move the Sun's image off the slit so the ROI window is dark by using the W-E buttons (in the case of scanning in RA; use the N-S buttons if scanning in DEC); (2) start acquisition ; (3) scan across the Solar disk using the W-E button; (4) watch the data signal appear and then disappear again and then halt the acquisition. If doing multiple scans, repeat the process (but it's important to stop and restart after each scan). If you are done with acquiring data, put the Sun's image back in the middle to slit so you don't lose the position.

I would suggest processing the first few scans right away in order to check things like scan speed, gain setting, and in particular the focus. If all the settings look good, I would recommend taking as many scans (back and worth) as possible in order to have some that will have "lucky imaging" and also due to the fact that inevitably there will be several where something went wrong. If you have enough good frames, you could try stacking but that's a more advanced process that isn't absolutely necessary.

Screenshot of H-alpha data acquisition
Screenshot of H-alpha data acquisition
H-alpha-desktop.jpg (177.33 KiB) Viewed 1113 times


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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by thesmiths »

To give an impression of what "good raw data" looks like (and also a typical fault), I attach here the reconstruction of a single SHG scan. In this example, the "geometry correction" is turned off so the image looks like a slightly rotated egg. The "transversalium correction" is also turned off so there are some fine horizontal lines visible. On the left side, there are obviously a large number of scans that somehow were not recorded (either a camera or computer error). Apart from resizing and turning into a jpg, there was not any additional processing done.

Uncorrected single SHG image
Uncorrected single SHG image
075901_clahe.jpg (117.1 KiB) Viewed 1110 times


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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by thesmiths »

Here is an image from a single SHG scan, rather than a stack of 5, as shown above. Perhaps not surprisingly, the stack evens out some noise but I see that a few fine details are also lost, when looking at a very small scale.

H-alpha image generated from a single scan.
H-alpha image generated from a single scan.
0845512_shift=0.jpg (448.45 KiB) Viewed 1099 times

I should mention that since this image is 1721 pixels wide, the average fps was 283, and the Y/X ratio was 0.948 (a slight overscan), the region spanned by this image took approximately 6.4 seconds to acquire (with each vertical line being acquired in 1ms).


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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by fulvio.mete »

Excellent images, Douglas, sincere congratulations for this result!
Fulvio


User avatar
hopskipson
Im an EXPERT!
Im an EXPERT!
Posts: 328
Joined: Sun Jan 13, 2019 9:27 pm
Location: Queens, NY
Has thanked: 404 times
Been thanked: 191 times

Re: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by hopskipson »

Thanks for the explanation of how you capture the images. I have been studying the Sol’Ex website and although it is informative the critical videos are all in French. Any insight into your set up and acquisition process would be very helpful. I have completed the construction and will be using a ST80 with 70 and 65 mm masks. I got an 82 mm 0.6 nd filter. The weather hasn’t cooperated to test it out yet but I was able to get get some images of the spectrum.

You set the exposure to 1 ms. At what rate did you scan the disk? I’m still learning this new technique, is it possible to see your set up?


James
These pretzels are making me thirsty! (C.C.)
The Quark introduced me to this wonderful side of the hobby and the sun hasn’t disappointed yet.
Solar Equipment: Solar Spectrum RG-18 0.3A, Coronado Solarmax 90mm etalon Isle of Man SN-001, Tuscon SN-380 and Meade SM2, Lunt LS80 DS, Quark Chromosphere, Lunt 2" wedge, 2-Lunt CaK II 1200, Baader 3.8 and 5.0 solar film in 208mm cells, and 3D printed Sol'Ex SHG, Lunt 40mm
Coming Soon: Solar Spectrum CaK II <1A filter
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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by thesmiths »

hopskipson wrote: Mon Jul 18, 2022 3:27 am You set the exposure to 1 ms. At what rate did you scan the disk? I’m still learning this new technique, is it possible to see your set up?
I've posted this photo elsewhere but I'll put it here also. This is how the setup looked last summer, but it hasn't changed too much on the outside. I'll try to take a new picture next time.

SHG on a 700mm FL refractor, HEQ5 Pro mount.
SHG on a 700mm FL refractor, HEQ5 Pro mount.
1151.jpg (250.71 KiB) Viewed 981 times

The scan rate depends on the focal length and FPS. At 700mm FL, I use 14 or 15 time sidereal rate. That corresponds to around 290 fps. I actually require the very short exposure of 1ms or less because I am not using an ND filter. The reason for not needing any attenuation is the custom made slit I am using (lithographically patterned chrome on fused quartz) that is more robust than the standard Solex slit. The Shelyak slits are, I think, made of normal glass.

With the ND filter of 0.6, you will get a 4x reduction in light, which means you should probably target an exposure of 4ms. That will give you an fps of 250. If your telescope has a 400mm FL, the image projected on the slit will be 4/7 of mine so the distance travelled to scan will be less. So I'm guessing you could scan up to a rate of 20x if you wanted. You might want to scan slower (like 16x) and bring the fps down to something like 200.

It turns out that it's very helpful if your mount is quite accurately polar aligned. Then there will be very little drift, which can complicate centering the sun on the slit for long periods of time.

Another easy mistake is misorienting the SHG so there is a lot of "tilt" in the images. The easiest way to get the orientation right is to put the telescope in the "home" position -- i.e. pointing towards Polaris. Then orient the SHG so the the flat sides of the SHG are either exactly vertical (for scanning in RA) or exactly horizontal (for scanning in DEC). The choice of which direction to scan in depends a lot on the mount. Most will scan better in DEC so I would do that. The images will then all be rotated by 90 degrees. Just by visually adjusting the orientation, you can get the "tilt" down to 1 or 2 degrees. You can improve this during measurement by noting that the scan should begin and end at the same position on the slit. That will get the "tilt" down to around 0.5 degrees.


User avatar
hopskipson
Im an EXPERT!
Im an EXPERT!
Posts: 328
Joined: Sun Jan 13, 2019 9:27 pm
Location: Queens, NY
Has thanked: 404 times
Been thanked: 191 times

Re: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by hopskipson »

Thank you again for the informative response! I guess I’ll try to search the archives for more details. Thanks again and good job with your set up.


James
These pretzels are making me thirsty! (C.C.)
The Quark introduced me to this wonderful side of the hobby and the sun hasn’t disappointed yet.
Solar Equipment: Solar Spectrum RG-18 0.3A, Coronado Solarmax 90mm etalon Isle of Man SN-001, Tuscon SN-380 and Meade SM2, Lunt LS80 DS, Quark Chromosphere, Lunt 2" wedge, 2-Lunt CaK II 1200, Baader 3.8 and 5.0 solar film in 208mm cells, and 3D printed Sol'Ex SHG, Lunt 40mm
Coming Soon: Solar Spectrum CaK II <1A filter
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: Improved H-alpha SHG high-resolution imaging from morning of 11 July

Post by marktownley »

Fascinating, with excellent results 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!
Post Reply