New Spectroheliograph construction (based on 102mm refractor)

[SunRick]

Hello,
I am new to this forum.....but I was encouraged to post my spectroheliograph construction details.
I started with a Sol'Ex spectroheliograph a couple years ago after retirement, and the images were very good paired with my old 80mm f/5 refractor stopped to 70mm. Retirement allows you to access the sun more! But, I wanted more. Aperture fever holds for solar too! The Sol'Ex experience allowed me to fully understand exactly how a spectroheliograph works. That helped me build a new spectroheliograph that would produce a full-disk solar image at higher resolution based on a 102mm f/7 APO refractor I had won in a grand prize drawing at the 2012 Winter Star Party in the Florida Keys. Luckily, Douglass Smith in England advised me greatly on this project. Without his guidance, it would have been much more difficult. The concept is the same as the Sol'Ex SHG....using a slit, collimating lens, diffraction grating, camera lens, and camera. But, it had to be scaled up! Other than the slit assembly (supplied by Smith) and a 3-D printed hoop (which I will explain later)......all components were "off-the-shelf".
First, here is list of components I used:
- 102mm f/7 Explore Scientific APO refractor
- 12mm x 9 micron chrome-on-quartz slit already mounted in a 1.25-inch filter holder
- Two Pentax Takumar 150mm f/4 camera lenses (from eBay, made in the 1960's)
- Thorlabs 2,400 groove/mm holographic reflective diffraction grating - 50 x 50 mm
- ZWO ASI183mm camera
- Multiple Perspex (black acrylic) disks from eBay
- 3 black plastic grocery bags, a towel, and a couple twist-ties to cover the assembly and keep light out
- 3-D printed oval hoop to keep bag coverings out of the light path
- ADM 31-inch D-style dovetail plate (to mount all the components)
- ADM 7-inch V-series dovetail plate to mount camera/camera lens assembly
- 50mm finder holder with thumbscrews (use just one of the circles) to mount camera lens/camera assembly
- Lots of threaded spacer rings/adapters, bolts, washers, double-sticky tape, etc.
- Software (I use SharpCap for imaging, TheSmiths V4.3 for constructing sun image from scan videos, Autostakkert for stacking, and IMPPG for sharpening)
- 1 or 2 tb SSD in laptop computer replacing mechanical hard drive (to record video FAST!)
- AP900 QMD mount (already had that from the 1990's)

I attached an image of the assembly mounted on the AP900 QMD mount......both with and without "shroud.

SHG mounted without "shroud"

SHG without shroud.jpg (1.26 MiB) Viewed 9300 times

SHG mounted with "shroud"

high tech light blocking.jpg (1.11 MiB) Viewed 9300 times

Here is a close-up of the "business" end of the assembly:

Business end of the SHG assembly

SHG closeup.jpg (1.14 MiB) Viewed 9300 times

Here is a close-up of the diffraction grating taped to its stand and attached to acrylic disk "rotator" assembly:

Diffraction grating rotator assembly

SHG grating rotator closeup.jpg (796.31 KiB) Viewed 9300 times

There are procedures for assembly, like how to space the slit at the focus point of the collimating lens, how to focus the collimating lens, how to focus the camera lens and space the camera correctly, what angle to use for the camera lens, and getting all components on the same plane. For me, videos of just the spectral line (h-alpha for example) are recorded at 361 frames per second while the sun is being scanned at 16X sidereal speed. A long narrow ROI (region of interest) box surrounds the slightly curved spectral line to facilitate high framerates. I record an SER video of a scan N-S. Then, immediately record an SER video of a scan S-N. Rinse and repeat for maybe 10 minutes. Run the videos through TheSmiths software to construct sun images. Stack the sharpest images in Autostakkert (I stack 15 to 30). Open the stack in IMPPG and sharpen. The final image is finished (other than small brightness/curves/rotation tweaks)! You can create high-contrast 0.1 - 0.15 Angstrom bandpass, really detailed, full-disk images of the sun at multiple wavelengths. Just rotate the grating and slightly refocus camera lens and scope to image h-beta or calcium-H. The good news about the black grocery bags is you can rotate the grating and refocus the camera lens right through the bags without removing. I use 3 layers of bags to block more light.

Here is an h-alpha image from April 7th, 2024. Make sure to right-click image to open image in a new tab....and then click the + magnifier to view at full 3063 x 3006 resolution:

SHG h-alpha image 4/7/2024

Sun 4-7-24 new SHG h-alpha.jpg (2.61 MiB) Viewed 9300 times

Here is a calcium-H image from April 6th, 2024. Make sure to right-click image to open image in a new tab....and then click the + magnifier to view at full 1532 x 1535 resolution:

Calcium-H image 4/6/2024

Sun 4-6-24 new SHG calcium-H s.jpg (964.28 KiB) Viewed 9300 times

Any questions or more details, I will be glad to answer. Spectroheliographs were the original way to image the sun spectrally, and this modern amateur version pays homage to that original. Such a cool instrument.

Rick

[marktownley]

Hi Rick,

Welcome to the forum! That's a great setup that is producing lovely disks. Looking forward to seeing more!

[solarchat]

wow!

[rsfoto]

Stunning SHG images. No lines to see anywhere...

[SunRick]

Thanks Rainer,
I have found if the wind is relatively calm and the seeing is OK to good in the morning hours, I can usually get a good SHG image with no lines. Wind is the enemy of SHG's. If it is windy or bad seeing, the reconstructed solar images have a fine "sawtooth" pattern at the edges that can produce lines, especially obvious in filaments. These lines can be reinforced by Autostakkert trying to align them. On bad days, I can tell if the scans will have this problem.....because the spectral line video will look shaky at the edges. So, I try to avoid breezy days! Hopefully, more calm days will be coming over the next 6 months.

[Montana]

WOW!! these are stunning images

A very warm and sunny welcome and thank you for showing us the results

Alexandra

[Ivan]

Excellent Rick images!!! I even dare to assume that they are perfect. Bravo!

Ivan

[thesmiths]

Hi Richard, that's a great presentation. Your post-acquisition processing looks pretty perfected.

One thing that would be useful to see is a comparison with your previously taken Solex images. That would highlight the improvement in resolution that you achieved with your upgrade to the larger system.

I think starting out with a Solex is a great first step and many people will be perfectly satisfied with the results. But there is quite a bit that can be potentially gained with upscaling the optics. I think a 4-inch aperture is a real "sweet spot" for the SHG technique. I generally would not recommend going above 115mm aperture and in particular around 800mm focal length. Above 800mm creates a series of complications that makes full disk imaging much more difficult.

[SunRick]

Thanks Doug.
As you know, I did get started with Christian Buil's Sol'Ex spectroheliograph. It is a 3-D printed kit available from Azur3DPrint, with an optics set available from Sheylak (both in France). Or, you can 3-D print your own, as the files are available. Although the unit is about the size of a Telrad, it is capable of producing quite good solar images when paired with optics around 400 - 432 mm range. That is the upper limit for a full-disk solar image because the slit is only 4 mm wide. So, for instance, a good scope pairing might be refractors in the 70 - 80mm range with focal ratios in the f/5 to f/6 range. You will also need an equatorial mount that can slew at various speeds on command......like 16X sidereal for example. There are videos in English and French that detail exactly how to assemble the kit and install/adjust the optics. It is a great way to be introduced to the world of spectroheliography, and really helps you understand exactly how they work.
The images that can be obtained are darn good for the cost of the setup and the smaller optics (including inexpensive camera). I used a cheap 30-year-old 80mm f/5 achromatic refractor I had lying around unused for many years in my basement! A friend 3-D printed a 70mm aperture stop for image improvement. I used this happily for quite a while......until I saw Doug Smith's images with his larger refractor and homemade SHG! Thanks a lot, Doug!!!

Anyway.....for comparison, here is an example of a Sol'Ex h-alpha image I took on January 20th, 2024 using an 80mm f/5 refractor stopped to 70mm. Many folks would be pretty satisfied with solar images like this. It's a nice full-disk image:

Sol'Ex sHG h-alpha image 80mm f/5 stopped to 70mm

Sun 1-20-24 SHG h-alpha.jpg (699.62 KiB) Viewed 9157 times

Here is a pic of the Sol'Ex SHG mounted. See how compact it is.

Sol'Ex SHG mounted with 80mm scope

spectroheliograph.jpg (447.9 KiB) Viewed 9157 times

But, the upgrade to 102mm and building a homemade SHG was well worth it. The images are much better.

Rick

[SunRick]

Here are a couple other 102mm SHG images from this past month. I am amazed how well they are turning out. When folks ask what filter I use to get these 0.10 to 0.15 Angstrom h-alpha images......I say "no filter"! They are confused until I explain.

Here is a 102mm h-alpha image from 4/6/2024. Make sure to right-click and choose "Open image in new tab". Then, open that new tab and bring the + magnifier over the picture and click it. That should give you full resolution if your monitor zoom is set to 100%.

102mm SHG 4/6/2024

Sun 4-6-24 new SHG h-alpha.jpg (2.48 MiB) Viewed 9153 times

Here is a 102 mm h-alpha image from 3/28/2024.

102mm SHG h-alpha image 3/28/2024

Sun 3-28-24 new SHG h-alpha final.jpg (2.66 MiB) Viewed 9153 times

Rick

[thesmiths]

I should mention that the mount Richard used (AP900) seems to work really well for scanning. A lot of mounts don't seem to scan linearly with time, which leads to strange distortions.

[SunRick]

Hi Doug,

Just a lucky break on the mount. I have two mounts that I bought used decades ago built around 1997....an AP900 QMD and an AP1200 QMD.....for $1500 each. I've used both for a lot of deep-sky and planetary imaging. Either one would work fine for SHG'ing.....but that 1200 is a LOAD. I'm 65 years old now, and there seems to be a problem with gravity......as that mount gets heavier every year! So, I use the much lighter 900 QMD mount. It still barely notices the 23 lb. SHG assembly. I try to balance the DEC perfectly when I install the 31-inch ADM dovetail plate into the mount saddle, because I scan N-S. When comparing the N-S and S-N scans in TheSmiths software.....the Y/X values are virtually identical. That means scanning both directions to get more scans per unit time works well.

One interesting factoid is that these old AP QMD mounts use stepper motors instead of servo motors. They do not have go-to capability and cannot slew faster than 16X on the handpaddle. They are not as good as today's servo-motor AP mounts for periodic error, but maybe for scanning at 16X, they are more stable and maintain a consistent slew speed. I don't know for sure, because I don't have a new AP mount! But, hey.....those QMD's do have a solar tracking rate switch on the handpaddle!

Rick

[Dennis]

Wow, so thats how ca-k looks like : )
Great results.

[SunRick]

Hi Dennis,
Thanks! The calcium image is actually calcium-H, not calcium-K. But, the 2 strong calcium lines are very close to each other......just a few nanometers apart. The views and images are very similar between the two. Calcium-K has been traditionally used by researchers, because the hydrogen-epsilon line is very close to the calcium-H line......and they do not want "contamination". The h-epsilon line is 3970.0 Angstroms, and the calcium-H line is 3968.5 Angstroms. That's very close for typical calcium filters with bandpasses ranging from 2 to 4 Angstroms! But my SHG, with a resolution < 0.2 Angstroms, can isolate the center of the calcium-H line. Since calcium-H is closer to the visible spectrum than calcium-K, optical elements in the system (camera lenses and telescope) work a little better, as they generally are not well corrected for UV. Also, my ASI183mm camera has a little better sensitivity closer the the visible spectrum too. You would not believe how much scope focus and camera lens focus has to be adjusted when rotating the grating from h-alpha to calcium-H....and my scope is an "APO" refractor!
Finally, the calcium-H or K solar images do look much different compared to typical filtered images, as the effective bandpass of my SHG is 1/10th to 1/20th the width of typical Daystar and Lunt etalon filters. That gives much higher contrast and an "unfamiliar" look.

Rick

[SunRick]

Here are 3 solar images from today (h-alpha, h-beta, and calcium-H). I am getting into a rhythm of recording scans, rotating grating to different spectral line, refocusing camera lens and telescope, and recording scans. Then, repeat for calcium-H. Even with a 102mm APO scope, I am amazed how much I need to refocus both the camera lens and the scope itself between h-alpha and calcium in the UV. The optics are not optimized for UV.
Make sure to right click image and select "open in new window". Then, with magnifier showing +, click to expand. If monitor is at 100% zoom, the image will be at full resolution.

SHG h-alpha 4/13/24

Sun 4-13-24 new SHG h-alpha.jpg (2.47 MiB) Viewed 9046 times

SHG h-beta 4/13/24

Sun 4-13-24 new SHG h-beta.jpg (2.14 MiB) Viewed 9046 times

SHG calcium-H 4/13/24

Sun 4-13-24 new SHG calcium-H s.jpg (1016 KiB) Viewed 9046 times

Rick

[marktownley]

Thanks Rick! These are beautiful images, nice to compare your CaH and my CaK from the same day. You should try stopping the scope down to say 70mm when you are imaging in CaH.

[SunRick]

Hi Mark,
I do have a 71 mm stop for this scope (3-D printed), and I have tried it on calcium-H.....but I can't see a difference (or maybe full aperture is even a little better). The only difference is that I can turn the gain down substantially at full aperture when recording spectral line videos. I understand that most refractors are just not optimized for UV, and stopping down should be an improvement. But so far, I have not seen an improvement stopped down. Doug Smith advised me to do the same thing!

Rick

[y3000]

Which is the most significant factor in improving resolution compared to the original Solex? Telescope aperture, focal length, collimator and camera lens aperture, or grating size?

[thesmiths]

Which is the most significant factor in improving resolution compared to the original Solex? Telescope aperture, focal length, collimator and camera lens aperture, or grating size?

I think the most significant factor is telescope aperture (and also telescope quality, which is a different issue). You can use the Solex with a larger aperture, but then the focal length typically increases, which means you can no longer take a full disk image. You can easily attach the standard Solex to a 100mm f/7 telescope but the diameter of the Sun on the slit will be approximately 6.4mm, while the slit length of the Solex is only 4.5mm. So for a full disk, you would need to take two scans and blend them together (or just be happy with part of the disk).

The other issue with the standard Solex is the slit is apparently made from soda lime glass, which will crack under focused solar light. Both fused quartz and borosilicate glass are much more resistant to thermal cracking and survive focused sunlight with only a UV/IR filter in front of the slit. So the standard Solex requires using an ND filter on the front lens (or a Herschel wedge), which necessitates longer exposures or higher gains. (Another Solex option is to use a wide-band H-alpha filter in front of the slit but then of course you are limited to H-alpha.)

One other issue with Solex if you go through all the numbers is there is a tendency to either over or under sample; you have to be a bit careful with the choice of pixel size (something around 3 micron turns out to ideal, but this is not a size that's easily available). The design presented above has a quite optimised spatial and spectral spectral sampling ratio, which also contributes to the higher image quality.

But to return to your original question, if you increase the telescope aperture and want to still take a full disk image, you will need a longer slit, a longer focal length collimator, and a larger grating. You could actually modify the original Solex to accomplish this, but it's probably easier just to build something new from scratch.

[SunRick]

Here are another couple SHG images taken today. I imaged in h-alpha and calcium-H with the new spectroheliograph. The seeing was OK. After this, I won't keep posting images I take every clear day to overwhelm people......just the super good or cool ones! I am working on a presentation on how this system was put together that dives deeper into each component.

SHG h-alpha image 4/15/24

Sun 4-15-24 new SHG h-alpha.jpg (2.49 MiB) Viewed 8835 times

SHG calcium-H 4/15/24

Sun 4-15-24 new SHG calcium-H.jpg (1021.97 KiB) Viewed 8835 times

Rick Schrantz

[Montana]

Please do keep posting the images, I'm loving every single one

Alexandra

[y3000]

Which is the most significant factor in improving resolution compared to the original Solex? Telescope aperture, focal length, collimator and camera lens aperture, or grating size?

I think the most significant factor is telescope aperture (and also telescope quality, which is a different issue). You can use the Solex with a larger aperture, but then the focal length typically increases, which means you can no longer take a full disk image. You can easily attach the standard Solex to a 100mm f/7 telescope but the diameter of the Sun on the slit will be approximately 6.4mm, while the slit length of the Solex is only 4.5mm. So for a full disk, you would need to take two scans and blend them together (or just be happy with part of the disk).

The other issue with the standard Solex is the slit is apparently made from soda lime glass, which will crack under focused solar light. Both fused quartz and borosilicate glass are much more resistant to thermal cracking and survive focused sunlight with only a UV/IR filter in front of the slit. So the standard Solex requires using an ND filter on the front lens (or a Herschel wedge), which necessitates longer exposures or higher gains. (Another Solex option is to use a wide-band H-alpha filter in front of the slit but then of course you are limited to H-alpha.)

One other issue with Solex if you go through all the numbers is there is a tendency to either over or under sample; you have to be a bit careful with the choice of pixel size (something around 3 micron turns out to ideal, but this is not a size that's easily available). The design presented above has a quite optimised spatial and spectral spectral sampling ratio, which also contributes to the higher image quality.

But to return to your original question, if you increase the telescope aperture and want to still take a full disk image, you will need a longer slit, a longer focal length collimator, and a larger grating. You could actually modify the original Solex to accomplish this, but it's probably easier just to build something new from scratch.

I am currently using a modified version of Sol'ex, with a new slit(7um/13mm). Both the collimator and camera lenses use industrial lenses with a diameter of 42mm. My telescope is 90/600APO refractor, and camera uses QHY174M or 183M. The entire device include a camera, which weighs about 900g. Even uses with a 120/1000 refractor , it should be able to capture the full disk with 183m. So I just wonder if I want to continue improving resolution, should I consider to use the 120/1000 AR telescope or replace the collimator or camera lens with a larger aperture DC camera lens, like Pentax.

shg.png (319.2 KiB) Viewed 8776 times

[LLichter]

I am with Alexandra on this.

Please keep posting.
These images are awesome to zoom around.

[thesmiths]

I am currently using a modified version of Sol'ex, with a new slit (7um/13mm). Both the collimator and camera lenses use industrial lenses with a diameter of 42mm. My telescope is 90/600APO refractor, and camera uses QHY174M or 183M. The entire device include a camera, which weighs about 900g. Even uses with a 120/1000 refractor, it should be able to capture the full disk with 183m. So I just wonder if I want to continue improving resolution, should I consider to use the 120/1000 AR telescope or replace the collimator or camera lens with a larger aperture DC camera lens, like Pentax.

My rule of thumb is the collimator can support a focal length telescope 5.5 times as big. So an 80mm collimator will work ok with a telescope up to around 440mm focal length. So for your 90mm / 600mm telescope, I would use a pair of lenses (collimator and imaging) of 120mm or so (I would keep the focal lengths the same). The industrial lenses should be ok. You only need around f/5 lenses.

I would not recommend using the 120/1000 telescope. First of all, you will not see much improvement going from 90mm aperture to 120mm. Second, for a 1000m focal length telescope, you will need to a 200mm collimator, which is getting quite big. There are a number of other problems that will come up with at 1000mm focal length; I won't go into all of them, I will just tell you to avoid.

I guess you are using on of the Chinese 7 micron borosilicate slits. These are ok to use with no ND filter, just a UV/IR filter. Which size of grating are you using?

[y3000]

I am currently using a modified version of Sol'ex, with a new slit (7um/13mm). Both the collimator and camera lenses use industrial lenses with a diameter of 42mm. My telescope is 90/600APO refractor, and camera uses QHY174M or 183M. The entire device include a camera, which weighs about 900g. Even uses with a 120/1000 refractor, it should be able to capture the full disk with 183m. So I just wonder if I want to continue improving resolution, should I consider to use the 120/1000 AR telescope or replace the collimator or camera lens with a larger aperture DC camera lens, like Pentax.

My rule of thumb is the collimator can support a focal length telescope 5.5 times as big. So an 80mm collimator will work ok with a telescope up to around 440mm focal length. So for your 90mm / 600mm telescope, I would use a pair of lenses (collimator and imaging) of 120mm or so (I would keep the focal lengths the same). The industrial lenses should be ok. You only need around f/5 lenses.

I would not recommend using the 120/1000 telescope. First of all, you will not see much improvement going from 90mm aperture to 120mm. Second, for a 1000m focal length telescope, you will need to a 200mm collimator, which is getting quite big. There are a number of other problems that will come up with at 1000mm focal length; I won't go into all of them, I will just tell you to avoid.

I guess you are using on of the Chinese 7 micron borosilicate slits. These are ok to use with no ND filter, just a UV/IR filter. Which size of grating are you using?

Yes, I use the Chinese 7 micron slit, currently used without ND filter, even no UV/IR filter when came to CaH /CaK . The size of grating is 25x25x6mm, 2400l/mm.

[thesmiths]

Yes, I use the Chinese 7 micron slit, currently used without ND filter, even no UV/IR filter when came to CaH /CaK . The size of grating is 25x25x6mm, 2400l/mm.

A 25mm grating is ok for your setup, but if you decide to increase the focal length of the lenses, you will probably find you need to increase the size of the grating to at least 30mm square.

By the way, the minimum camera lens diameter is not something you should pay too much attention to. In fact, I would tend to not have the camera lens set with an f-ratio above 4 or 5 in order to minimise optical aberrations.

Also, you should take note of the grating minimum width figure, which tends to be much larger than the minimum height, especially at H-alpha. The wider the grating, the more light it will intercept when the grating is at a high angle. It's not crucial to capture all the light, but a wider grating is helpful.

[SunRick]

Today, I recorded 3 wavelengths with my new spectroheliograph described above. The morning was calm and clear, so the seeing was pretty good (for April). I imaged the standard h-alpha and calcium-H, but I tried something different with the third image...the Magnesium I (b2) line at 5172.7 Angstroms. There are three strong spectral lines near each other in the green part of the spectrum (all magnesium). This is the middle of the three lines. Anyway, take a look and see what you think.
- The first image is h-alpha at full resolution. Make sure you look at it at full resolution (right-click image to open image in a new tab....and then click the + magnifier to view at full 3003 x 2970 resolution and pan around). Stack of 40 scans.
- The second image is calcium-H. It has been reduced from full resolution. Stack of 17 scans.
- The third image is Magnesium I (b2). It is at full resolution. Single scan
The magnesium view is interesting. This wavelength shows the dark absorptive mottling of the chromospheric network plus plage plus large scale magnetic structure. However, I could only post a single scan, because features changed so rapidly, an Autostakkert stack of 20 scans simply smoothed out the chromospheric network, while enhancing the more stable plage! Scrolling through the images showed significant change over 30 seconds. Oh well. So, the magnesium image is not as good, but you can see the structure. There are some weird vertical lines at both edges (parallel to the slit).
See all the fun you can have with a spectroheliograph? You can think (I'll go and check out magnesium today.....and then do it)! OK, so I'm a geek.

Sun 4/18/24 new SHG h-alpha

Sun 4-18-24 new SHG h-alpha.jpg (2.28 MiB) Viewed 8571 times

Sun 4/18/24 new SHG calcium-H

Sun 4-18-24 new SHG calcium-H.jpg (1.09 MiB) Viewed 8571 times

Sun 4/18/24 new SHG magnesium I (b2) single scan

Sun 4-18-2024 new SHG magnesium 1-b2.jpg (3.06 MiB) Viewed 8571 times

Rick

[thesmiths]

The magnesium view is interesting. This wavelength shows the dark absorptive mottling of the chromospheric network plus plage plus large scale magnetic structure. However, I could only post a single scan, because features changed so rapidly, an Autostakkert stack of 20 scans simply smoothed out the chromospheric network, while enhancing the more stable plage! Scrolling through the images showed significant change over 30 seconds. Oh well. So, the magnesium image is not as good, but you can see the structure. There are some weird vertical lines at both edges (parallel to the slit).

The H-alpha and Ca-H are really good (especially the H-alpha, which shows incredible details).

The vertical lines at the left and right edge of the Magnesium are transversalium lines (since your scan is north/south). Near the edge of the Sun, our software does not do a good job of transversalium removal (because there is little "baseline" for the filter near the edges -- however, you could play with the transversalium strength, which I think you have set quite low). When you do stacking, a lot of instrumental defects will tend to average out because there will be small shifts between frames. But a single frame will show all the defects, and any sharpening will increase their visibility.

[SunRick]

Thanks Doug. Transversalium lines are vanquished in my h-alpha and calcium images with a slider setting of just 1.0. However, the magnesium solar image was filled with wide faint horizontal bands. I had to set the slider at 6 or 7 to get rid of them! Why the difference? Is it because the magnesium image was pretty evenly toned compared to h-alpha, so faint bands stick out like a sore thumb? Thanks.

Rick

[thesmiths]

Why the difference? Is it because the magnesium image was pretty evenly toned compared to h-alpha, so faint bands stick out like a sore thumb?

Yes, the lack of contrast on magnesium could be the difference. But also, I suspect, the lack of stacking.

[Montana]

Oh my!!! like a sweetie pic and mix all are fabulous in my book even the magnesium. We very rarely get the other lines to sit and ponder on, thank you!

Alexandra

[SunRick]

Here is another h-alpha image from today. I still can't believe all the very narrow bandpass detail that can be had on a full-disk image. The large sunspot group on the sun today is filled with detail when looking at the image at full resolution (3021 x 2970). This SHG is just too cool. It's way more fun than a conventional solar scope if you are mostly interested in imaging. I attached a reduced h-beta image too. I am still working on getting that a bit better.

SHG h-alpha 4/20/24

Sun 4-20-24 new SHG h-alpha.jpg (2.3 MiB) Viewed 8373 times

SHG h-beta reduced 4/20/24

Sun 4-20-24 new SHG h-beta reduced.jpg (870.25 KiB) Viewed 8373 times

Rick Schrantz

[marktownley]

Lovely additions thanks!

[SunRick]

Just finished the new SHG calcium-H image from yesterday. 102mm f/7 full aperture.

Rick Schrantz

SHG calcium-H 4/20/24

Sun 4-20-24 new SHG calcium-H reduced.jpg (1.19 MiB) Viewed 8330 times

[Montana]

It's lovely to hear how excited you are
and of course the beautiful images

Alexandra

[John]

Congratulations on your super SHG Halpha image on Spaceweather yesterday.

John

[SunRick]

Here are a couple SHG images from today. I still can't believe I can record good full-disk images most days when it is not windy. What would a commercial 102 mm scope cost that recorded a full disk solar h-alpha image with a 0.1 - 0.2 Angstrom bandpass? If it was even available......way more than the SHG!! Plus, this is more fun. I can't wait for the actual good summer morning seeing conditions later this year (Kentucky, USA).

Images today.......best 30 of 42 video scans over a 10 minute span constructed in TheSmiths V4.3 software and stacked in Autostakkert 3 and sharpened in IMPPG. Scanning both N-S and S-N directions results in more scans per minute. I can get about 4 scans per minute this way. The h-alpha image is full resolution and not reduced. View it at full resolution on a large desktop monitor (right click on image, open new link in window, click "+" magnifier on image to view at full resolution (monitor set at 100% zoom factor).

SHG Image h-alpha 4/22/24

Sun 4-22-24 new SHG h-alpha.jpg (2.58 MiB) Viewed 8227 times

SHG image calcium-H 4/22/24

Sun 4-22-24 new SHG Calcium-H reduced.jpg (1.2 MiB) Viewed 8227 times

Rick Schrantz

[Montana]

Incredible filaments in the Calcium H
You are very lucky indeed to have everything working perfectly, most people really struggle.

Alexandra

[SunRick]

Thanks Alexandra!
It may not be luck, because I had the guidance of a black-belt "sensei" of this type of spectroheliograph......Doug Smith in England.
I started with a Sol'Ex, and that enabled me to understand the concept of the SHG. When I saw Doug's SHG images, I wanted that too (who wouldn't?). Since I happened to have a spare 102mm f/7 refractor I was not using, I emailed him about how to do this project. I looked at his detailed posts about his 106mm SHG, and I thought it was do-able. I emailed Doug constantly asking about details of every component, so I could basically order the same thing! I asked him how he constructed and assembled stuff.....what adapters to get, how to attach the grating (even what tape he used), how to orient the grating, what spacing he used for the focal point of the lenses and how to focus the collimating lens assembly, what model of Takumar lens to get on eBay, how he mounted the imaging lens, how to get the rotation of components correct, what camera to use, what his processing flow looked like, etc. I did not want to re-invent everything when Doug had already done all that work!

Doug never failed to respond and provided detailed emails. I bet he was tired of seeing yet another email from me in his inbox! I am certain I could not have done this project without his constant advice.....and a slit he designed and sold to me.....and his great processing software! Of course, as any amateur astronomer would do, I made a few changes that worked better for me. For example, I mounted everything on a 31-inch ADM D-style dovetail plate, while Doug used several smaller V-style dovetails. I found a 50mm finder ring set that fit like a glove over the threaded ring that comes with the ZWO camera.....so I used that to mount the imaging lens assembly (Doug used a camera bellows he found). Really, there were just a few minor differences like those.
So, I was pretty confident everything would work together after I assembled and adjusted stuff, because it was very similar to what Doug already successfully did.
I am taking photos now and will create posts that detail each subassembly separately.

Rick

[SunRick]

Since my mount was already set up on the back patio (left there from yesterday).....I decided to SHG-image even though winds were 14 mph and gusting to 22 mph. I normally would not have set up in these conditions. I had some wind protection from the house, but that meant the winds were blowing over the hot shingles toward me. With the Sol'Ex, I would get the infamous "jagged edges" effect in these conditions. The black plastic bags were fluttering with constant crinkly sounds! But, to my surprise, the finished image turned out very nicely! There were no jagged edges in the individual scans. I know that wind is the enemy of SHG-imaging, but I may need to reset my assumptions regarding how much wind is too much!

I attached the h-alpha image from this morning.

SHG h-alpha image (4/23/24)

Sun 4-23-24 new SHG h-alpha.jpg (2.33 MiB) Viewed 8175 times

Rick

[Montana]

Absolutely superb and thank you for the explanation. Doug needs a Gold astronomy award for services to the SHG

Alexandra

[SunRick]

Spectroheliograph Construction Details

Part-1: Telescope:
Over multiple posts, I will try to give construction details and tips for each subassembly of a spectroheliograph that works well and gives super detailed solar images at super narrow bandpass. I will do separate posts about:
- The telescope and mount
- The collimating lens assembly (including slit)
- The diffraction grating assembly
- The camera lens assembly
- How to put everything together and adjust
- Acquisition and processing software

This post is about the telescope and mount:

To record super detailed SHG full-disk solar images at multiple wavelengths, the right telescope needs to be chosen. It has to be dedicated to the SHG, since once it is installed and adjusted and connected, it is not coming off! I use an Explore Scientific 102mm f/7 ED/APO telescope at 714 mm focal length. It's not "top-of-the-line" for APO telescopes, as it uses FPL-51 glass and not FPL-53. This scope is 12 or 13 years old. Communications with Doug Smith reveal that around 4 inches aperture and around 700 - 800 mm focal length is the sweet spot for this type of SHG. Larger aperture or longer focal lengths create problems, like larger lenses and diffraction grating needed, etc. Luckily, this aperture/focal length is common among many scope manufacturers (like Explore Scientific, ZWO, Askar, Astro-Tech, and others).
The mount needs to be a sturdy equatorial variety. It has to have solar tracking rate. The total assembly I built weighs 23 lb. and is 31 inches long....so the mount has to handle that weight. It needs to have a slew speed around 16X sidereal. My old AP900 QMD mount built in the 1990's fits the bill, but the slew rates are limited to 8X and 16X. It is not a go-to mount. But, it resists a light breeze well. See pics at start of topic for mount and scope images.

Next up will be the camera assembly.

Rick

[SunRick]

Spectroheliograph Construction Details

Part 2: Camera Lens Assembly

The camera lens assembly is the part of the spectroheliograph angled and aimed at the diffraction grating. See images at start of this thread. It is the assembly that images the spectrum produced by the grating.....from which a full-disk solar image is formed.

A 150mm f/4 Pentax Takumar camera lens (made in the 1960's) is used. This old manual camera lens is readily available on eBay for $50 - $100 price range in very nice condition. This lens has 42mm threads on the back mounting end, but do not choose the EMC model, as it has more "doo-dads" on the back end. Pick a lens in mint or near mint condition. No lens fungus or clouding or scratches! The back end should not look heavily used.
The camera lens attaches to a fast video camera. The ZWO ASI178mm is reasonably priced, but the chip is just a little too small. So close! Use the larger chip ASI183mm (which other than chip size/# of pixels is identical to the 178). Unfortunately, it is significantly more expensive.

You need to connect the camera lens to the camera using adapter/spacer threads. The chip needs to be maybe 1 mm inside the back-focus distance to allow for focus adjustment. Unfortunately, the 42mm threads of the Takumar lens are 42x1mm pitch. Standard T-threads are 42mmx0.75mm pitch. Really? Oh, come on!!

So, first, you screw a 42X1mm female to 42X0.75mm male adapter ring on to the back of the lens. Then screw on the 11mm F to F thread ring that comes with the ZWO camera. Then screw on other T-thread rings so that the backfocus to the camera chip from the lens flange is about 43 to 44 mm. (The listed backfocus for this lens is 45.46 mm). Don't forget the chip backfocus from the camera flange of 6.5 mm.

Put a 2-inch h-alpha filter (with tape) or a cheaper 49mm red filter on the camera lens.
Then, plug in the camera on your laptop and aim it at distant clouds. Carefully focus the cloud video image and mark the infinity focus point on the focus ring with a piece of tape. You should have some focus wiggle room, which you will need.

See attached image of camera lens assembly with labels for clarity.

SHG Camera Lens Assembly

camera lens assembly.jpg (814.15 KiB) Viewed 8081 times

Next up will be the collimator assembly.

[SunRick]

Here are a couple spectroheliograph images from today using the SHG described in this thread. h-alpha and calcium-H. The seeing was medium, and there was some breeze (12 mph).

Sun in h-alpha SHG 4/25/24

Sun 4-25-24 new SHG h-alpha.jpg (2.49 MiB) Viewed 8038 times

Sun in calcium-H SHG 4/25/24

Sun 4-25-24 new SHG calcium-H.jpg (1.08 MiB) Viewed 8038 times

Rick

[thesmiths]

I decided to SHG-image even though winds were 14 mph and gusting to 22 mph. I normally would not have set up in these conditions. I had some wind protection from the house, but that meant the winds were blowing over the hot shingles toward me. With the Sol'Ex, I would get the infamous "jagged edges" effect in these conditions. The black plastic bags were fluttering with constant crinkly sounds! But, to my surprise, the finished image turned out very nicely! There were no jagged edges in the individual scans. I know that wind is the enemy of SHG-imaging, but I may need to reset my assumptions regarding how much wind is too much!

I have found that stacking "averages out" a lot of the irregularities at the solar edge. And I guess the stacking program also is able to fix quite a lot of the distortions that occur on the solar surface.

A 150mm f/4 Pentax Takumar camera lens (made in the 1960's) is used. This old manual camera lens is readily available on eBay for $50 - $100 price range in very nice condition. This lens has 42mm threads on the back mounting end, but do not choose the EMC model, as it has more "doo-dads" on the back end. Pick a lens in mint or near mint condition. No lens fungus or clouding or scratches! The back end should not look heavily used.

Small correction: the model *not* to use is the SMC model (Super-Multi-Coated -- product code 43742). The one to use is the older Super-Takumar model (product codes 43740 and 43741). I've tested a lot of vintage lenses and this one is "magical" for SHG (a combination of high sharpness, moderate weight and superb built-in focuser). https://www.pentaxforums.com/lensreview ... mm-F4.html

[SunRick]

Oops.

I meant to not use the Takumar 150mm f/4 "SMC lens".....instead of "EMC lens". Fat fingers!

Rick

[SunRick]

Spectroheliograph Construction Details

Part 2: Collimating Lens Assembly

I consider the collimating lens assembly to be the "lynchpin" of the spectroheliograph. It is the most difficult part to get right, and it is most critical. The previous camera lens assembly was relatively easy to understand. Attach a camera to a camera lens, get the back-focus spacing correct, and focus at infinity. Bada-Bing, Bada-Boom! It's all very intuitive.

However, the collimating lens assembly is more complicated and not necessarily intuitive. The assembly consists of 2 parts.....the "slit" and the collimating lens. The concept is this: A slit is attached to a Pentax Takumar 150mm f/4 camera lens, and spaced at its back-focus distance. Then, the assembly is mounted in a telescope focuser with the slit end facing the telescope. Finally, the solar image from the telescope is focused on the slit.

Well, great concept....but how is all this this accomplished?

Step 1:
Obtain a nice slit assembly from SHG sensei Doug Smith in England. The one I purchased from him is 12mm x 9 micron chrome-on-quartz. And, it is nicely mounted in a 1.25-inch threaded filter cell.

Step 2:
Attach the slit to a Pentax Takumar 150mm f/4 camera lens. Threaded adapters and spacers will have to be used for this. The Pentax lens has 42 x 1mm threads on the back end. You will screw a 42 x 1mm F to 42 x 0.75mm M adapter to it. You will also have to use a 42mm x 0.75mm (T-thread) spacer that has 1.25-inch filter threads internally into which the slit assembly is screwed. Finally, attach a T-thread-to-2-inch barrel adapter that can slide into your scope focuser or another extension tube. T-thread extension rings should be used so the lens back-focus distance to the slit is about 43 - 44 mm. This gives a little focus adjustment room. Place a red or h-alpha filter on the 2-inch barrel or the front of the camera lens (to optimize adjusting collimator lens focus for h-alpha).

Step 3:
Aim the collimating lens assembly into the camera lens assembly (which was previously adjusted to infinity focus). Space the two lenses facing each other about 2 or 3 inches apart, and adjust them straight and horizontal at the same level. This can be tricky. Aim the slit at an illuminated white piece of paper.

Collimating lens focus adjustment

Collimating lens adjustment.jpg (1.23 MiB) Viewed 7774 times

Step 4:
Attach the camera to a computer and start it. Rotate the collimating assembly and adjust collimating lens focus so the slit image is razor sharp and horizonal and centered on the computer screen looking at the full CMOS chip. Then, zoom the resolution to 100% and tweak focus perfectly. Spend some time on this, and get it right. You only need to do it once. Once focused, carefully tape the collimator lens focus ring so the focus is locked in place. This does not change.

Focused slit image on computer monitor

silt image on monitor.jpg (535.02 KiB) Viewed 7774 times

Step 4:
Remove the red filter and screw an Astronomik L1 UV/IR blocking filter into the extension tube barrel. This is to protect the slit, while still giving a little extra room for calcium UV images. But, before screwing on the filter, make sure you clean any dust off the slit by air-puffing it with a squeeze-bulb. The slit must be clean (but don't touch it with anything other than the puff from a squeeze-bulb). Immediately screw on the filter, and that should permanently seal the slit from dust.

This finishes the collimator assembly. It slides into the scope focuser, and is the only part of the SHG supported by the scope focuser.

Collimating assembly with labels

collimating assembly with labels.jpg (411.06 KiB) Viewed 7774 times

Doug Smith ....please comment on anything I missed or got wrong.

Rick

[SunRick]

Here is an h-alpha image from today. It turned out well, considering it was a breezy day again. I can't wait for the calmer winds and better seeing of late spring and summer!

Sun 4-28-24 new SHG h-alpha

Sun 4-28-24 new SHG h-alpha.jpg (2.37 MiB) Viewed 7773 times

Rick

[y3000]

Which F-number of lens should be set ? F4 or small number ?

[thesmiths]

Part 2: Collimating Lens Assembly

Step 3:
Aim the collimating lens assembly into the camera lens assembly (which was previously adjusted to infinity focus). Space the two lenses facing each other about 2 or 3 inches apart, and adjust them straight and horizontal at the same level. This can be tricky. Aim the slit at an illuminated white piece of paper.

Doug Smith ....please comment on anything I missed or got wrong.

That's a very good description of the collimator assembly. As you mention, aligning the two lenses facing each other is rather tricky. I actually align them with the front of the two lenses touching. You could actually get a little more sophisticated and buy a pair of 49mm to 42mm adapters (49mm is the filter thread of that generation of lenses) which is called a "macro lens inverter" (commonly found on eBay). You could then build a small adapter that would connect the two lenses together more solidly. I actually use a little LED flashlight aimed at the slit (rather than the angled sheet of paper you mention). This is both very bright and also a more focused light beam (more similar to the light cone coming from the telescope).