New Spectroheliograph construction (based on 102mm refractor)

[thesmiths]

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

You should keep the collimator wide open (e.g. f/4) to avoid vignetting of the slit. The f-ratio of the collimator is actually set externally by the f-ratio of the telescope (e.g. f/7)

I actually typically set the camera lens at f/5.6 since this is where most camera lenses of this generation are the sharpest. This does decrease the light intensity slightly so you might want to operate at f/4 in order to minimise the camera exposure time and gain.

[SunRick]

Spectroheliograph Construction Details

Part 4: Diffraction Grating Assembly:

The concept of the diffraction grating assembly is to receive sunlight from the collimating assembly, split the sunlight into a rainbow of colors, and send that rainbow to the camera lens assembly. This takes the place of an interference filter as a way to isolate particular wavelengths of interest (such as h-alpha in the red and calcium-H/K in the near-UV). In addition, this grating needs to be rotatable so the spectral absorption line of interest is shown on the camera chip.
Good concept, but how do we make it happen? Here is what I did.

Step 1:
Procure a diffraction grating. Not just any grating will do, though. It has to be sized and specified correctly. The type of grating to get is a reflective holographic diffraction grating optimized for visible light, 2400 grooves per mm, at a 50mm square size x 9.5mm thick. The particular grating I got is a Thorlabs model GH50-24V. Warning.....this grating surface is very sensitive, and the surface cannot be touched with your fingers or cleaned in any way. Only blow off dust with a squeeze-bulb air puffer. Keep covered and protected when not in use.

Step 2:
Procure a number of circular black Perspex (acrylic) disks available in 3mm or 5mm thickness on eBay (https://www.ebay.com/itm/125772123733?var=426766328807). One of the disks should be 80mm diameter and 5mm thick. The other disks should be 3 and/or 5 mm thick x 70mm diameter.....depending on how much you need to raise the grating when assembled to match the level of the lenses.

Step 3:
Procure an ADM VPA-V Series Dovetail Adapter (https://www.admaccessories.com/product/ ... l-adapter/). Unscrew one side of the clamp and remove it. The remaining solid piece stood upright becomes the perfect mount for the grating.

Step 4:
The final step is putting the grating assembly together. Drill and tap 1/4x20 center holes in all the Perspex acrylic disks. Drill and countersink a hole in one of the 70mm x 5mm disks at a specific location to attach the ADM mount. Drill and tap a hole on the short "L" side of the ADM mounting piece so that, when attached to the 70mm disk, the front face of the grating is exactly over the middle of the center hole. Tape the back side of the grating to the ADM mount face using 3M double-sticky tape. The bottom of the grating will rest on the angled edge of the ADM mount. Multiple disks are screwed on to the base plate of the SHG with a 1/4x20 bolt. The 80mm x 5mm disk should be second from the top. The multiple disks can be screwed against each other so that they are locked and rotate as a unit to adjust the angle of the grating.

Diffraction grating assembly without grating mounted

SHG final pivot view.JPG (743.75 KiB) Viewed 1500 times

Diffraction grating assembly back view

SHG final back view.JPG (841.34 KiB) Viewed 1500 times

Diffraction grating assembly with grating attached

SHG grating rotator closeup.jpg (796.31 KiB) Viewed 1500 times

Rick

[SunRick]

FYI......here is another h-alpha SHG from today in breezy conditions.

SHG h-alpha 4/29/24

Sun 4-29-24 new SHG h-alpha x.jpg (2.62 MiB) Viewed 1499 times

Rick

[Montana]

I wish I were clever enough to build and use one

Alexandra

[thesmiths]

Part 4: Diffraction Grating Assembly:

Step 4:
The final step is putting the grating assembly together. Drill and tap 1/4x20 center holes in all the Perspex acrylic disks. Drill and countersink a hole in one of the 70mm x 5mm disks at a specific location to attach the ADM mount. Drill and tap a hole on the short "L" side of the ADM mounting piece so that, when attached to the 70mm disk, the front face of the grating is exactly over the middle of the center hole. Tape the back side of the grating to the ADM mount face using 3M double-sticky tape. The bottom of the grating will rest on the angled edge of the ADM mount. Multiple disks are screwed on to the base plate of the SHG with a 1/4x20 bolt. The 80mm x 5mm disk should be second from the top. The multiple disks can be screwed against each other so that they are locked and rotate as a unit to adjust the angle of the grating.

This is an excellent description how to mount a 50mm square diffraction grating. I should mention that the ADM VPA adapter is less useful for smaller gratings (like 25mm or 30mm square). Something more custom-made (e.g. 3D printed) would need to be made for smaller ones. But for 50mm, it's an almost ideal shape and it is quite cost-effective considering it is precision machined aluminium and black anodised.

The "Scotch permanent double sided tape" used to attach the grating to the ADM holder is very strong and effective. But it is so strong that if you do want to remove the grating for some reason, it can be a real problem. For that reason, I tapped the two rear through holes with an M8 thread and got some M8 x 16mm bolts. That way, I can use the bolts to push the grating off, rather than have to pull the grating off. By the way, I would recommend getting a pair of white cotton gloves (used for handling photographic negatives and slides) to attach (or detach) the grating.

You could also use the tapped holes on the back of the ADM VPA to install some sort of long lever to help rotate the grating. I don't typically do this (I just rotate the plastic disk by hand) but I have in the past put on a long bolt (with a nut on the back side to secure it). But if you do put torque on the ADM VPA, it needs to be very securely attached to the plastic disk (either with two screws or I have also used cyanoacrylate glue).

2111.jpg (191.61 KiB) Viewed 1460 times

[SunRick]

I wish I were clever enough to build and use one

Alexandra

Hi Alexandra,

You ARE clever enough to build and use one! Actually, you don't have to be very clever to do this (I'm not). That is why I am posting details on how to construct one, including separate sections on several sub-assemblies. A lot of the clever work has been done already (especially by Doug), so you don't have to "re-invent the wheel". You will notice that, except for the slit from Doug Smith, all the pieces-parts are off-the-shelf items. There are still more sections to come about mounting all the subassemblies to create a complete SHG.....including creating the "darkness" around the lenses and grating. And, of course, all the software to use from recording spectral line videos to processing the final image.

Using an SHG is not hard if all the components are optimized. To record with an SHG, basically, I just:
- Look for a sunny, calm (or light breeze) morning.
- Put the 23 lb. SHG unit on my mount and balance it.
- Uncap the lenses and scope and uncover the grating. Blow off with hand-bulb air puffer.
- Aim the scope at the sun.
- Cover assembly with multiple black grocery bags (I'll have a section on that).
- Connect the camera, start the imaging software, and locate the sun's spectral image.
- Center the h-alpha line (for example) by rotating the grating.
- Tweak focus on the camera lens to make the spectral lines razor-sharp
- Tweak scope focus to make solar edge sharp and make h-alpha line detail as sharp as possible.
- Set up ROI box on the software to enclose spectral line in a long narrow ROI box.
- Start recording spectral line videos over and over as you are slewing N-S back and forth at 16X. Record for about 10 minutes (about 40 videos).

That's it. Sounds like a lot, but it goes very fast, and it's not hard. I'll have more details in a special imaging section post.

Please ask me any questions you have, or ask Doug Smith.....as he is the SHG master.

Rick

[SunRick]

Spectroheliograph Construction Details

Part 5: Putting Everything Together:

So far, I have reviewed construction of the Camera lens assembly, the collimating assembly, and the grating assembly.....plus the telescope and mount requirements. But, how does one put all these components together to make a working SHG unit?

Here is the concept: A solar image is focused by the telescope on a slit. The light passing though the silt is passed through a collimating lens directed to the diffraction grating. The grating splits the sunlight into a spectrum with hundreds/thousands of absorption lines. The grating is rotated so that the camera lens assembly (mounted at an angle) images the spectral line of interest. The telescope is slewed across the sun as the spectral line is being video recorded at high speed. Special software reconstructs a sun image from the spectral line scan video.

Here is how I mounted everything to make the above concept happen:

Step 1:
Procure an ADM 31-inch D-series universal dovetail bar (https://www.admaccessories.com/product/ ... 2-spacing/). You will need a mount saddle on your mount that can accept a D-series dovetail bar. This makes a great platform that is just the right length as the base of your SHG.

Step 2:
Mount your telescope to one end of the 31-inch dovetail bar. The exact location of the scope can be adjusted by changing mounting holes or sliding the scope back or forth in its mounting rings. The center of your scope focuser becomes the level at which all other components of the SHG must be aligned with. I also bolted a spare unused male-male dovetail plate to the 31-inch bar to add altitude to other components. I would not do this if I didn't have it already and was not worried about the extra weight (of the plate.....not me!).

Step 3:
Slide the collimating assembly barrel into the scope focuser. The collimating assembly should have the correct extension tubes on it so that the scope can be focused on the slit without racking out the scope focuser very much (better stability). This scope focal point can be determined by measuring distance from the objective or simply aiming at the sun and focusing the sun on a small rock. Disclaimer: don't burn yourself; don't look through the scope at the sun; don't use anything combustible when focusing the sun......yada, yada, yada. You know the drill.

Step 4:
Procure a 7-inch ADM V-series universal dovetail bar (https://www.admaccessories.com/product/ ... ar-7-long/). This is bolted perpendicularly on the 31-inch bar, and will hold the camera lens assembly at about a 30 degree angle.

Step 5:
Procure a 50mm guidescope ring set. By that, I mean the internal diameter of the ring is 50mm (https://www.walmart.com/ip/Adjustable-P ... =101241625). Using one of the rings on this set is perfect to hold the camera lens assembly if you use the ASI camera's 11mm spacer ring as one of the lens back-focus spacers. That spacer ring is 49.5mm OD. The ring fits it like a glove! Mount the ring to the 7-inch dovetail bar so that the camera lens assembly is the correct height and the angle to the grating is about 30 degrees. This will require something to elevate the ring. I just used a stack of washers.

Overall Back End Assembly

overall back end assembly.jpg (2.49 MiB) Viewed 1403 times

Step 6:
Mount the diffraction grating assembly to the base using the 1/4-inch bolt that passes through the disks. That bolt should be flush with the top disk surface. You may have to cut a bolt to size. Adjust the friction with the base so the disks have plenty of friction to hold the grating angle securely, but are still easily turnable by grabbing the rim of the 80mm disk that protrudes out from the stack of 70mm disks. The diffraction grating should be about 4 inches from each lens.

SHG Closeup

SHG closeup.jpg (1.14 MiB) Viewed 1403 times

Step 7:
A light blocking system needs to be used to enclose the lenses and diffraction grating in darkness during imaging. I found that 3 black plastic grocery bags nested inside each other works very well! They are just the right size to pull over the back end of the SHG and over the camera and collimating lenses. I then twist the bag handles together with a bread bag twist-tie. This still leaves gaps down the length of the assembly, so I then fold and wrap a darker towel between the scope focuser and the collimating assembly extension tubes.....covering any gaps. This crude method of blocking light has one big advantage. I can adjust the camera lens focus, diffraction grating angle, and even camera rotation by grabbing those components right through the bag! I did have a friend 3-D print a hoop to keep the bags out of the light path.
Of course, there are a number of ways to accomplish light blocking......from plastic bags to cloth drawstring bags, to constructed or 3-D printed enclosures. Use your imagination!

SHG without grocery bags.

SHG without shroud.jpg (1.26 MiB) Viewed 1403 times

"High-Tech" Light Blocking

high tech light blocking.jpg (1.11 MiB) Viewed 1403 times

In the next posts, I will summarize component adjustments to make a good image and software/hardware used for recording and processing scan videos.

Are we having fun yet? Yes. Yes we are!

Rick

[SunRick]

The sun today was much easier to SHG h-alpha image with calm winds/light breeze. The finished solar image was significantly sharper (at full resolution). Cirrus clouds came in before I could image any other spectral line.

Sun 5-1-24 h-alpha spectroheliograph

Sun 5-1-24 new SHG h-alpha.jpg (2.5 MiB) Viewed 1355 times

Rick Schrantz

[rbotero]

Fantastic guide (and images to back it up) Rick - and guidance from Doug. Thank you for sharing this.

Roberto

[SunRick]

Spectroheliograph Construction Details

Part 6: Component Adjustment:

OK.....everything on the SHG is put together the way it is supposed to be. Everything is mounted optically on the same level and aimed correctly. The camera lens with camera installed is focused at infinity (and taped down) and angled about 30 degrees. The collimating assembly is focused according to previous procedure (and taped down). The scope is positioned and extension tube(s) added to the focuser so the focal point of the scope is right at the slit location. The Astronomik L1 UV/IR blocking filter is screwed onto the extension tube. The collimating assembly is rotated in the scope focuser so the slit is vertical with respect to the mounting plate (that makes the slit east-west). The grating is installed about 4 inches from each lens and angled appropriately.

Great! So, how do you adjust the SHG to optimize it so you are ready to start recording images? Here's how:

Step 1:
Install the 31-inch D-style dovetail plate of the SHG on to your mount saddle. Balance it in both RA and especially DEC.

Step 2:
Turn the scope drive on (set to solar rate). Aim the scope at the sun and minimize the shadow of the scope on the ground.

Step 3:
Remove the camera lens covers and the scope cover. Carefully remove the grating cover last.

Step 4:
Install the black bags (or other light blocking) to the back end of the SHG so the lenses and grating are in darkness.

Step 5:
Connect the camera to your computer (which must have a large SSD as the main drive.....1tb or greater).

Step 6:
Start the imaging software (either SharpCap or FireCapture). I use SharpCap because I am very familiar with it. Set the resolution at full camera chip view.

Step 7:
Turn up the gain and/or exposure until you see some light on the screen. Move the scope in RA toward the direction of brighter light. Move the scope in DEC toward the direction of brighter light. Eventually, the overexposed spectrum will show up on the monitor. You are on the sun!!!!

Step 8:
Reduce the exposure/gain until you see a spectrum.

Step 9:
Rotate the camera assembly until the spectrum edge is exactly vertical on your monitor. Then, rotate the collimating assembly until the spectral lines are exactly horizontal.

h-alpha line in solar spectrum

h-alpha big spectrum.jpg (198.77 KiB) Viewed 1285 times

Step 10:
Move the scope in RA until the spectrum hits the edge of the CMOS chip. Move the scope the other direction in RA until the spectrum hits the other edge of the CMOS chip. This shows you the chip boundaries. If the boundary edges are not centered on your screen, you are not aimed directly at your grating, and you need to adjust the angle of the camera assembly.

Step 11:
Tweak the focus of the camera lens until the spectral lines are sharp and in focus. (you will need to remove the tape locking down the focus first). Zoom to 100% to focus the spectral lines. Then, revert the zoom to "Auto".

h-alpha spectral line

h-alpha spectral line.jpg (40.65 KiB) Viewed 1285 times

Camera lens focus at 100% zoom h-alpha line

camera lens focus.jpg (76.32 KiB) Viewed 1285 times

Step 12:
Move the scope in RA until the edge of the spectrum is near the field of view center. Focus the telescope until the edge is sharp, and the spectral line detail is also sharp. If you are perfect, you will also see sharp delicate "transversalium lines". Then, recenter the spectrum.

Scope focused on h-alpha line

h-alpha scope focus.jpg (71.09 KiB) Viewed 1285 times

Step 13:
Familiarize yourself with rotating the grating slowly while watching the monitor. You will not believe how many spectral lines there are! Learn to recognize prominent spectral lines so you know where in the spectrum you are: You will learn by sight these prominent spectral lines starting at the red end: h-alpha in red, sodium doublet in yellow, the 3 magnesium lines in green, h-beta in blue, and the two wide and bold calcium lines in the near-UV.

Next, I will list the steps needed to begin an imaging session and what to do to record spectral line videos.

Rick

[SunRick]

Here are a couple more SHG images from May 2nd. Finally, the seeing was good, and it made a significant difference in the final images.

h-alpha SHG image

Sun 5-2-24 new SHG h-alpha.jpg (2.51 MiB) Viewed 1283 times

calcium-H SHG image

Sun 5-2-24 new SHG calcium-H.jpg (1.07 MiB) Viewed 1283 times

Rick

[Montana]

Yes, this post is a keeper!!

Fantastic images and step by step guide
Alexandra

[thesmiths]

Part 6: Component Adjustment:

Step 9:
Rotate the camera assembly until the spectrum edge is exactly vertical on your monitor. Then, rotate the collimating assembly until the spectral lines are exactly horizontal.

Step 10:
Move the scope in RA until the spectrum hits the edge of the CMOS chip. Move the scope the other direction in RA until the spectrum hits the other edge of the CMOS chip. This shows you the chip boundaries. If the boundary edges are not centered on your screen, you are not aimed directly at your grating, and you need to adjust the angle of the camera assembly.

I'll add a few more suggestions. When initially setting up for an imaging session, I turn on the "reticule" function in FireCapture. That way I can find the centre of the sensor (where generally the imaging will be better). This also helps in the "rotating the camera step" to make sure the edge of the sun is vertical and the "rotation of the slit" (via the collimating assembly) to make sure the spectral lines are horizontal. By the way, if you have a big enough camera sensor, you can move the mount a bit left/right and because the spectral line is curved, you can "level" the spectral that way.

Speaking of the curved spectral lines: the lines are approximately parabolic due to a well-know optical distortion common to this sort of spectrometer. The peak of the parabola always points towards the blue. By convention, blue is generally up and red down, so the parabola is typically pointing in the direction shown in the images above. If it pointed in the opposite direction, there is no real difference but the spectrum may be a little harder to interpret vs other users' data. You can reverse the orientation by rotating the camera by 180 degrees.

The comment in Step 10 is again only relevant if you have a big enough camera sensor (e.g. IMX 183). With a smaller sensor (e.g. IMX 178) you will have a fairly restricted left/right region in which you can move. Actually, the "edge of the spectrum" is generally the edge of the slit (not the edge of the grating). With a big sensor, you will actually be able to see both ends of the slit. As mentioned, you ideally want the slit to be centred on the camera sensor. If it's not, there is a slight tilt in the optical axis defined by the collimator, grating and camera lens. This can be fixed by tilting one of those three elements. The one that's most commonly out of alignment is the vertical angle of the diffraction grating. This could be adjusted by putting a small shim under the grating holder, but this is not so easy. If your camera lens has some up/down tilt alignment, this is by far the easiest.

[solarGain]

This again is all indoors today…I have gotten successfully this far as Part 6: Component Adjustment in Step 9 but I am unable/ unclear as to how with the spectrum bands laying horizontally that I can see fine spectral lines and if I’m lucky to be able to see transversalium lines. Again I must be doing something wrong and I do not wish to derail this excellent extensive posting.

John

[SunRick]

Thanks Doug,
You said it way better than me. Yes, I meant to say edge of the slit.....not edge of the grating. Thanks for good clarification. I'm still learning!
Rick

[SunRick]

This again is all indoors today…I have gotten successfully this far as Part 6: Component Adjustment in Step 9 but I am unable/ unclear as to how with the spectrum bands laying horizontally that I can see fine spectral lines and if I’m lucky to be able to see transversalium lines. Again I must be doing something wrong and I do not wish to derail this excellent extensive posting.

John

Hi John,
When the slit rotation (via the collimator assembly rotation) is correctly rotated, the spectral lines will be horizontal on your monitor. By "horizontal", I mean that the slight parabolic curve in the lines is level, and there is no overall tilt in one direction or the other.
Transversalium lines are very fine lines that can be seen in a spectrum (especially at 100% zoom) perpendicular to the spectral lines caused by dust or slight imperfections in the slit. If everything is focused correctly, they show up on the spectrum. Because they are so fine, if focus is off just a little bit, they will disappear. Seeing them "pop in to view" when focusing is a good sign that focus is achieved.

Doug can explain transversalium lines way better than I can, as his "TheSmiths" software has a feature that vanquishes them.

Rick

[SunRick]

Spectroheliograph Construction Details

Part 7: Imaging:

With everything set up correctly and aimed at the sun and focused correctly and looking at the spectrum on the monitor....it is time to start taking pictures! But, how do we do that?

Step 1:
Isolate the spectral line of interest (let's say h-alpha). This was done >100 years ago with a slit that matched the spectral line and a film plate moving under it. But, with the "ROI" feature of SharpCap (the imaging software I use) a "virtual slit" can be created. First, rotate the grating until the h-alpha line is centered on your monitor. Specify an ROI box size of 3208 pixels wide x 92 pixels high (what I use with my ASI183mm camera). You want to encompass the full width of the solar spectral line with room to spare on each end, and still encompass the curve of the spectral line with enough ROI height to spare. Leveling your spectral line allows you to minimize the height of the ROI box. Make sure you are set to video record at 16 bit.

Step 2:
Adjust the exposure, frame rate, and gain so you are around 360 frames per second (if your scan rate will be 16X sidereal N-S). That means your exposure can be no more than 1/360 = 2.78 milliseconds. You have to adjust gain so that your spectrum looks somewhat overexposed. Remember, you are imaging a dark spectral line. A good guide is the thin line directly below the h-alpha line should be overexposed except toward the ends of the spectrum. You will have to play with the "Turbo USB" slider to get the frame rate you want. Gain close to zero (or at least not more than 80) is best. All this framerate, exposure, gain, and Turbo USB adjustment requires some playing around your first time imaging so you get comfortable with these settings. You cannot directly adjust framerate, but there is a readout. Remember, you need an SSD on your laptop to get this high framerate. Some folks use FireCapture software to record videos, but I am not familiar with that software.

h-alpha line correctly exposed

h-alpha line.jpg (34.01 KiB) Viewed 1193 times

Step 3:
With the h-alpha line centered in the ROI box, and the mount speed set at 16X sidereal rate......move the mount north while watching the spectral line. It will narrow down until it is gone. Keep moving for another second or 2. the ROI box will be dark. Start the recording and watch the framerate readout. As soon as you see it reach 360 fps, start moving the mount south. The h-alpha line will appear and get wider, and then get narrower, as the slit is scanned across the disk of the sun. When it disappears, hold the scan for another second or 2 and stop. Stop the recording. Hopefully, there have been zero dropped frames.

Step 4:
Immediately start a new recording. As soon as you see the fps hit 360, start moving the mount north at 16X. Then, stop the recording when the h-alpha line disappears.

Step 5:
Rinse and repeat over and over again. After about 10 minutes you should have 40 SER videos taking up just over 100 gigabytes of SSD space. You are done recording!

Depending on your mount speed and exact scope focal length, your framerate will have to be calculated for your specific setup. Luckily, Doug Smith's "TheSmiths" software does this for you. Run a spectral video through it, and it will provide a "Y/X" ratio. This tells you how to adjust the framerate. If your Y/X=1.10, you need to increase the framerate by 10%. Eventually, you will know the framerate that gives a Y/X of 0.97 to 0.99 range (a little oversampled). Try to avoid >1.00 Y/X value.

Next time, I will post details on software used to process your SHG videos.

Doug, please make any comments or correct any mistakes I made. I know these numbers are all variable for each setup, but this is what I use for mine.

Rick

[thesmiths]

Part 7: Imaging:

Step 4:
Immediately start a new recording. As soon as you see the fps hit 360, start moving the mount north at 16X. Then, stop the recording when the h-alpha line disappears.

Step 5:
Rinse and repeat over and over again. After about 10 minutes you should have 40 SER videos taking up just over 100 gigabytes of SSD space. You are done recording!

Depending on your mount speed and exact scope focal length, your framerate will have to be calculated for your specific setup. Luckily, Doug Smith's "TheSmiths" software does this for you. Run a spectral video through it, and it will provide a "Y/X" ratio. This tells you how to adjust the framerate. If your Y/X=1.10, you need to increase the framerate by 10%. Eventually, you will know the framerate that gives a Y/X of 0.97 to 0.99 range (a little oversampled). Try to avoid >1.00 Y/X value.

"Immediately start a new recording": this may not be the best advice, depending on your equipment. First of all, I think some mounts take a bit of time to either "settle" or "recover" from slewing. Rick has a very good mount so likely does not have to worry about this. The second issue is the combination of the acquisition program and the computer may take some time to finish writing the video data to the SSD. If the video buffer gets filled up, the acquisition program can sometimes halt taking new data and there will be a gap in the scan. To avoid these issues, I always wait 5 seconds after a scan is finished before starting a new one.

I generally don't take more than about 20 scans at a time. I think there is diminishing returns and if there is too much time between the first and last scan, I think some solar features can change a bit. My target is to get around 15 good scans for stacking.

A range of Y/X ratio of 0.95 to 1.05 is quite acceptable.

For H-alpha, I actually try to target 18x to 20x sidereal rate scanning (since near 400nm the image is dimmer, the scan rate ends up being much slower). My Skywatcher HEQ5 Pro mount can slew at any integer multiple when controlled by ASCOM (I use the EQMOD program), but many other mounts don't have that flexibility. But in general, around 16x is a good value for H-alpha. My reasoning for trying to scan as fast as possible is that I think most environmental noise has a 1/f spectral distribution so if you can push the signal frequencies up in range, you will not notice the noise as much.

[SunRick]

I generally don't take more than about 20 scans at a time. I think there is diminishing returns and if there is too much time between the first and last scan, I think some solar features can change a bit. My target is to get around 15 good scans for stacking.

Hi Doug,
The reason I take about 40 scans over 10 minutes is because then I can choose which 20-scan segment of the 40 scans to use for stacking. I know everyone's imaging site has different characteristics. From my location, seeing can be quite variable on a calm day. Sometimes, if it is completely calm, the solar seeing will not be as good. Then, just a very slight, almost imperceptible breeze will kick in for a few minutes, and the seeing will get much better. Maybe that sets up a laminar air flow of some sort?? I know this from years of hi-resolution solar imaging at 5,100 mm focal length on my back patio. The problem with the SHG is that you really do not know when the seeing might get better for a while.....and a larger sequence of SHG videos increases my odds of being able to pick the best shorter segment. Of course, that means more computer SSD space is used.....and I can record 500GB on a nice solar day!
That being said.....sometimes I can get a clue about the seeing by watching the scans. I do notice poor seeing can make the scan videos more "jittery" looking. But, also, I don't think my laptop can display 360 frames per second either, so that can contribute to the jitteriness.

Thanks for all your good SHG comments! I am still learning.

Rick

[SunRick]

"Immediately start a new recording": this may not be the best advice, depending on your equipment. First of all, I think some mounts take a bit of time to either "settle" or "recover" from slewing. Rick has a very good mount so likely does not have to worry about this. The second issue is the combination of the acquisition program and the computer may take some time to finish writing the video data to the SSD. If the video buffer gets filled up, the acquisition program can sometimes halt taking new data and there will be a gap in the scan. To avoid these issues, I always wait 5 seconds after a scan is finished before starting a new one.

Hi Doug,

All good comments!
You are right that I don't experience the slew settling of some mounts. Of course, my crusty old AP900 QMD mount cannot slew to an object and is not go-to. It cannot go faster than 16X. That's a big disadvantage in a mount, but may actually be an advantage for SHG imaging.

As for the "immediate" starting of a new recording, it actually takes me a few seconds to click the commands to make that happen. Then, after the recording starts, I watch the framerate stabilize at my target framerate before I push the 16X slew button on my hand controller. Sometimes it takes a couple seconds to stabilize, but those few seconds of recording at the wrong framerate just record darkness! What I should have said is "As soon as everything has stabilized, start a new scan".

On a related note, I just got a new 17-inch HP Windows-11 laptop and had the original small SSD replaced with a new Samsung 2tb PCIe NVMe SSD. But, when I connect the ASI183mm camera to the USB3 port, the frames per second will read 360 for maybe 20 seconds and then drop off to 100 fps.....and then rev back up to 360 fps a couple second later. It repeats that pattern at random intervals from 5 seconds to 60 seconds. All this is in "preview" mode (not recording), so it is not a recording issue. This makes it unusable for SHG imaging, and I don't know how to fix it.
Meanwhile, the laptop I use for SHG imaging is my wife's old "scrap-top" Windows-10 computer with a broken Wi-Fi! I reclaimed it by replacing the hard drive with a 1tb SATA SSD (which is supposedly slower than my new laptop's SSD). Yet, the "scrap-top" works like a champ, and virtually never slows down the FPS when in use. This certainly frustrates me, as I would like to be using my new laptop!

Rick

[thesmiths]

On a related note, I just got a new 17-inch HP Windows-11 laptop and had the original small SSD replaced with a new Samsung 2tb PCIe NVMe SSD. But, when I connect the ASI183mm camera to the USB3 port, the frames per second will read 360 for maybe 20 seconds and then drop off to 100 fps.....and then rev back up to 360 fps a couple second later. It repeats that pattern at random intervals from 5 seconds to 60 seconds. All this is in "preview" mode (not recording), so it is not a recording issue. This makes it unusable for SHG imaging, and I don't know how to fix it.

With SharpCap, you need to make sure you are connecting to the camera with the ZWO driver and not the ASCOM driver. Also, check that the DRAM buffer is set to around 50% of the total system memory (e.g. 8 GB of 16GB). It's probably a SharpCap issue of some sort. To verify that it is, try using the native ASI Cap program (it always seems to get the fastest out of ZWO cameras, although it is lacking in features).

[SunRick]

Spectroheliograph Construction Details

Part 7: Image Processing:

The final step in my SHG journey is image processing. There are a lot of valid ways to process images, but for solar SHG, the general process is to:
- Create sun images from scans
- Stack a certain number of sun images for better S/N ratio.
- Sharpen the stacked image

So, how do I do all those things? Here's how:

Step 1:
Assuming all your scan videos are in a single folder......create a second folder. Move every other scan to this second folder. That segregates your N-S scans from your S-N scans.

Step 2:
Create sun images from the spectral line videos using Doug Smith's "TheSmiths" software (yes, that's really the name). The software has a "folder input mode". Select it so you can batch process your videos. Then, select the first folder your N-S videos are in. I check the boxes as follows:

TheSmiths software

TheSmiths software.jpg (123.33 KiB) Viewed 1145 times

Of course, you can play with the options of checking different boxes to familiarize yourself with it. Doug recommends using the lowest transversalium line correction you can (on the slider bar) and still eliminate these lines. I am very fortunate that I can use a 1.0 value. Other folks will have to use a higher value. It all depends on how much dust or other defects are on your slit. Doug also recommends setting the ellipse fit shift to 10.
Then, watch the software chug! Keep an eye on "Y/X" values and "unrotation angle theta". Unrotation should be less than 1 degree. Zero is perfect. You may also select "de-vignette" to see if it gives you a better image.
When the software has completed the processing, select the second folder. Process through "TheSmiths" the exact same way....EXCEPT....check the "Mirror X" option box. After the second folder has finished processing, move the contents of that folder back to the original folder. All your constructed sun images should be oriented the same.

Step 3:
The next step is stacking. Stack your images using Autostakkert software. I set the boxes and options like this:

Autostakkert

Autostakkert.jpg (130.03 KiB) Viewed 1145 times

The sun image will be huge! Place your stabilization anchor box around some strong features. Click "Analyze". After the software is finished analyzing, it will rate the "quality" of each image, and the sharpest image will be displayed.
Then, I set up the Autostakkert imaging box like this:

Autostakkert Image Box

AS Image Box.jpg (27.04 KiB) Viewed 1145 times

Click "Place AP grid". Over 10,000 alignment boxes will be auto-placed on the image! Scroll around the limb of the sun and manually click on dimmer prominence areas the software may have missed. This places alignment boxes around them.
Choose the number of frames to stack, and then click "Stack". The software stacks them by highest quality. Solar imagers know that the sun boils and flexes, so Autostakkert works stacking miracles by stacking alignment boxes separately, and then recombines them into the finished stack.
Now you have a very high signal-to-noise ratio stacked image saved as a 16-bit TIF file.

Step 4:
The next step is sharpening. I like IMPPG software. This free software uses both Lucy-Richardson and unsharp masking to sharpen. Open the stacked 16-bit TIFF file. It's huge! Although there are many ways to set up the option box, I set it up like so:

IMPPG Option Box

IMPPG option box.jpg (31.81 KiB) Viewed 1145 times

When you are satisfied with the image sharpness of the small selection square, make sure and click the "process the whole image" icon. The entire image is sharpened with your selected options. Move different sliders up and down to see how the finished image responds. Sharpen it to your liking and save the sharpened image as a 16-bit TIF file.

Step 5:
Repeat after me: "I will never, EVER over-process a solar image. The best processed image looks as though it was never even processed".
We have all seen over-processed solar images. How do you know if an image is too sharp or over-processed? I just looks "unnatural" (too noisy, too mottled, too much contrast, too sharp, etc.). There is no particular definition, but after some experience, you will "know it when you see it"! Save the processed image as a 16-bit TIF file.

Step 6:
The final step is using your favorite image software to crop some of the black border out if it is too thick, add some descriptive text if you wish, tweak the brightness. contrast, or curves if you wish......and save the final result as a minimum compression jpeg file. I am not a fan of adding fake orange color to an h-alpha image. So, I just leave my images B&W mono.

I hope you liked my summary of building an SHG, mounting it, adjusting it, imaging with it, and processing the final solar image. I thank Doug Smith, my SHG mentor, for adding some valuable comments.
As an aside, these instruments are just too cool, and they are not hard to build and use. You will have an instrument that can provide an ultra narrow-band solar image that is narrower bandpass than any filter can provide. You will gain enormous "street-cred" in your astronomy club!

And, most importantly, you will have the pleasure of resurrecting the original solar narrow-band imaging technique that George Ellery Hale himself invented in his 1890 Physics bachelor's degree thesis at MIT (it was also independently invented by Deslandres in 1892 and refined by McMath in 1932).
Here is Hale's thesis in his own handwriting from MIT's database:
https://dspace.mit.edu/handle/1721.1/43574

So, enjoy! I know I do.

Rick Schrantz

[thesmiths]

Part 7: Image Processing:

Step 1:
Assuming all your scan videos are in a single folder......create a second folder. Move every other scan to this second folder. That segregates your N-S scans from your S-N scans.

Step 2:
Create sun images from the spectral line videos using Doug Smith's "TheSmiths" software (yes, that's really the name). The software has a "folder input mode". Select it so you can batch process your videos. Then, select the first folder your N-S videos are in.

When the software has completed the processing, select the second folder. Process through "TheSmiths" the exact same way....EXCEPT....check the "Mirror X" option box. After the second folder has finished processing, move the contents of that folder back to the original folder. All your constructed sun images should be oriented the same.

I should mention an alternative way to process scans that are taken in both directions (either N-S or E-W). First of all, I always define an Output Folder so that the output files (typically PNG files) do not get mixed up with the input data (typically SER files). I normally use File input mode and select every second file (e.g. the odd number ones) to process in the "Normal" direction and then process the other files (the even number ones) in the "Mirror" direction. I do this by using CTRL and mouse click:

control click.JPG (83.03 KiB) Viewed 1119 times

Also, I always use the "Rotate png images" function to save an additional step later. If you scan in DEC, then output images will at some point need to be rotated by either 90 degrees or 270 degrees (it depends on which side of the Meridien your telescope is on, by the way). If you scan in RA, the the rotation will be either 0 or 180 degrees.

If you are taking a full disk scan, then I recommend using "Crop square" so that all the PNG frames will be the same size. Stacking programs require all the images to have the same dimensions. You can also stack what I call "partial disks", but then you will have to manually tell the program how wide you want all the images to be (since the field of view will be rectangular instead of square).

[SunRick]

Hi Doug,

Thanks for all your good comments. I appreciate the extra info, because I only know my specific situation and equipment, while you have good info for a more broad audience with varying equipment.....plus alternate ways to accomplish things that could be easier!

Rick

[SunRick]

On a related note, I just got a new 17-inch HP Windows-11 laptop and had the original small SSD replaced with a new Samsung 2tb PCIe NVMe SSD. But, when I connect the ASI183mm camera to the USB3 port, the frames per second will read 360 for maybe 20 seconds and then drop off to 100 fps.....and then rev back up to 360 fps a couple second later. It repeats that pattern at random intervals from 5 seconds to 60 seconds. All this is in "preview" mode (not recording), so it is not a recording issue. This makes it unusable for SHG imaging, and I don't know how to fix it.

With SharpCap, you need to make sure you are connecting to the camera with the ZWO driver and not the ASCOM driver. Also, check that the DRAM buffer is set to around 50% of the total system memory (e.g. 8 GB of 16GB). It's probably a SharpCap issue of some sort. To verify that it is, try using the native ASI Cap program (it always seems to get the fastest out of ZWO cameras, although it is lacking in features).

Hi Doug,
I loaded the latest ZWO driver on the new laptop and also loaded ASICap recording software. I see the same issue. The framerate is stable around 365 fps for a minute or two.....then drops to near zero and back up again to 365 all in about 2 seconds. Then, maybe 20 seconds later does it again. Then, maybe a minute later does it again.....etc. I get the same behavior in SharpCap. This laptop is much better than the old one I am using that has no issues like this. The SSD is faster and larger, and there is more RAM (12GB) in the new laptop.
When you said "check that the DRAM buffer is set to around 50% of the total system memory (e.g. 8 GB of 16GB)".....I understand the concept, but I am not sure how to proceed. I googled it, and I am still confused. How do you check this and how do you set it?
Thanks.

Rick

[SunRick]

On a related note, I just got a new 17-inch HP Windows-11 laptop and had the original small SSD replaced with a new Samsung 2tb PCIe NVMe SSD. But, when I connect the ASI183mm camera to the USB3 port, the frames per second will read 360 for maybe 20 seconds and then drop off to 100 fps.....and then rev back up to 360 fps a couple second later. It repeats that pattern at random intervals from 5 seconds to 60 seconds. All this is in "preview" mode (not recording), so it is not a recording issue. This makes it unusable for SHG imaging, and I don't know how to fix it.

With SharpCap, you need to make sure you are connecting to the camera with the ZWO driver and not the ASCOM driver. Also, check that the DRAM buffer is set to around 50% of the total system memory (e.g. 8 GB of 16GB). It's probably a SharpCap issue of some sort. To verify that it is, try using the native ASI Cap program (it always seems to get the fastest out of ZWO cameras, although it is lacking in features).

Hi Doug,
I loaded the latest ZWO driver on the new laptop and also loaded ASICap recording software. I see the same issue. The framerate is stable around 365 fps for a minute or two.....then drops to near zero and back up again to 365 all in about 2 seconds. Then, maybe 20 seconds later does it again. Then, maybe a minute later does it again.....etc. I get the same behavior in SharpCap. This laptop is much better than the old one I am using that has no issues like this. The SSD is faster and larger, and there is more RAM (12GB) in the new laptop.
When you said "check that the DRAM buffer is set to around 50% of the total system memory (e.g. 8 GB of 16GB)".....I understand the concept, but I am not sure how to proceed. I googled it, and I am still confused. How do you check this and how do you set it?
Thanks.

Rick

Hi Doug,

I think I fixed my new laptop problem with fps randomly slowing down and speeding back up when using my ASI183mm camera. I had neglected to delete all the programs HP put on the startup menu that I do not use. So, when I did that and restarted the laptop.....and disconnected from the internet......the problem was gone. I ran SharpCap in preview mode for 10 continuous minutes, and the fps never dropped at all.....solidly staying at 363 fps. Heck, over those 10 continuous minutes, zero frames were dropped!

So, sorry I bothered you about this topic. Clearing the startup menu of programs I do not use is routine for me.....but for some reason, I forgot this time. I hear this gets worse the older one gets!!!!

Rick

[thesmiths]

I think I fixed my new laptop problem with fps randomly slowing down and speeding back up when using my ASI183mm camera. I had neglected to delete all the programs HP put on the startup menu that I do not use. So, when I did that and restarted the laptop.....and disconnected from the internet......the problem was gone.

Another good idea is to go to the Task Manager (ctrl-alt-del) and then to the tab called "Startup". Change to "Disabled" everything you don't think you need running when you are taking data (sort by "Status"). You'll find almost every program installed will want to be running in the background (maybe to spy on you? I have no idea why). Or is that what you did already?

[SunRick]

I think I fixed my new laptop problem with fps randomly slowing down and speeding back up when using my ASI183mm camera. I had neglected to delete all the programs HP put on the startup menu that I do not use. So, when I did that and restarted the laptop.....and disconnected from the internet......the problem was gone.

Another good idea is to go to the Task Manager (ctrl-alt-del) and then to the tab called "Startup". Change to "Disabled" everything you don't think you need running when you are taking data (sort by "Status"). You'll find almost every program installed will want to be running in the background (maybe to spy on you? I have no idea why). Or is that what you did already?

Hi Doug,

Yep, that's what I did. It worked wonders!

Rick

[SunRick]

Finally, for the first time in 10 days, the morning weather was good for solar imaging. The seeing was actually quite good with calm winds. I was able to SHG-image the sun in h-alpha and calcium-H, with sunspot 3664 about ready to rotate off the face of the sun. Also, I tried SHG-imaging in calcium-H at both full 102mm aperture and stopped down to 72mm (about f/10). In the past, I could see no difference between the two, so I imaged full aperture. But, with very good seeing this morning.....there was definitely an improvement in sharpness stopped down to 72mm. I always knew there should have been, but I just was not able to get that improvement in the past. I think it was seeing related.....with the atmosphere just not allowing that sharper image stopped down.

So, here are those two images in h-alpha and stopped down calcium-H. Make sure to look at them full resolution!

On a side note, I hope everyone got to see the aurora Friday night. I live in Kentucky, USA (37.8 degrees N), and I sat outside in the middle of my lawn and saw auroras all over the sky. I even saw and took pics of them on the southern horizon! Vivid reds in the sky everywhere. My head was on a swivel. I actually had to stop my lens down because at f/2.8 and 8-seconds, by CMOS chip was saturated by the bright auroras. The pink part of the aurora was on top of the the crescent moon and actually overwhelmed it! Auroras imaged down to Mazatlán and even Puerto Rico.

102mm f/7 SHG h-alpha image

Sun 5-12-14 new SHG h-alpha.jpg (2.72 MiB) Viewed 910 times

72mm f/10 SHG calcium-H image

Sun 5-12-14 new SHG calcium-H.jpg (2.28 MiB) Viewed 910 times

Rick

[thesmiths]

Also, I tried SHG-imaging in calcium-H at both full 102mm aperture and stopped down to 72mm (about f/10). In the past, I could see no difference between the two, so I imaged full aperture. But, with very good seeing this morning.....there was definitely an improvement in sharpness stopped down to 72mm. I always knew there should have been, but I just was not able to get that improvement in the past. I think it was seeing related.....with the atmosphere just not allowing that sharper image stopped down.

Your images are consistently very, very good. What a nice reliable instrument.

Are you using the imaging lens (on the camera) full open (at f/4)? Or do you close it down a bit? I think images do sharpen up a bit if you reduce to around f/5.6, but there is then a reduction in image brightness which necessitates a longer exposure and/or higher camera gain.

[SunRick]

Your images are consistently very, very good. What a nice reliable instrument.

Are you using the imaging lens (on the camera) full open (at f/4)? Or do you close it down a bit? I think images do sharpen up a bit if you reduce to around f/5.6, but there is then a reduction in image brightness which necessitates a longer exposure and/or higher camera gain.

Thanks Doug,

The reason I have a reliable SHG instrument is because I followed your instructions and email replies! That took the guesswork out of building it. I use the imaging lens at f/5.6 and the collimating lens at f/4. Those were your recommendations, so that's what I do! At f/5.6, I can image at 361 frames per second with a gain ranging from 0 to 40 on h-alpha. With calcium-H stopped down to 72mm, I use a gain of around 60. The relative darkness of the calcium recording means the gain does not have to be too high. I am lucky that everything works well at 16X scan rate, because, other than 8X.....that's all I've got! I can comfortably adjust everything while looking at the monitor because the black plastic grocery bags covering the setup allow me to grab anything I want while still keeping things in darkness.

Rapidly switching to different spectral lines is becoming routine. I:
- Go back to full-chip view on the monitor
- Grab the rim of the 90mm acrylic disk and rotate the grating while watching the monitor
- Recognize the line I want and center it
- Go back to narrow ROI box and switch to 200% view.
- Focus the spectral lines by focusing the imaging lens through the black grocery bags
- Move the RA so the sun edge shows at the center of the chip
- Focus the scope so the edge is sharp and the spectral line shows detail. I do not have electric focus. No problemo!!
- Return the spectrum ROI to "auto" view (which shows it all) and recenter it
- Move through a scan and watch to make sure no bright areas of the spectral line are overexposed
- Adjust gain accordingly
- Start recording scans!

Bada Bing....Bada Boom! This all takes maybe 2 or 3 minutes if I take my time.

I just love this SHG. It's such a cool instrument. Thank you for making this a do-able project for me.

Rick

[thesmiths]

I can comfortably adjust everything while looking at the monitor because the black plastic grocery bags covering the setup allow me to grab anything I want while still keeping things in darkness.

- Grab the rim of the 90mm acrylic disk and rotate the grating while watching the monitor
- Recognize the line I want and center it

I recently tried something new that worked quite well: that is, attach a short lever to one of the black plastic discs. This made it both easier to grab and also allowed a finer rotational motion to more precisely place the line.

[Albireo]

Hi Rick,

incredible instrument and incredible results!
Seeing your images makes me want to follow up on getting my own SHG.
While I do get jealous of your resolution, I guess starting with a Sol'Ex makes more sense instead of building my own? I have an older Orion Shorttube 80 (f/5) scope and a ASI174MM which I could readily use. Any other scope / camera I would have to buy in addition to the SHG.

I'm looking forward to seeing your pictures! Have you ever tried to make a dopplergram or even a magnetogram? Or to image HeI?

Cheers,
Jan

[thesmiths]

I guess starting with a Sol'Ex makes more sense instead of building my own? I have an older Orion Short tube 80 (f/5) scope and a ASI174MM which I could readily use.

I would generally recommend starting with the Solex before building something bigger. A 400mm focal length telescope is a good fit for the Solex. The 174MM will work, although the pixels are a bit on the large size. The 178MM actually has pixels that are too small for the classic Solex.

[Albireo]

I would generally recommend starting with the Solex before building something bigger. A 400mm focal length telescope is a good fit for the Solex. The 174MM will work, although the pixels are a bit on the large size. The 178MM actually has pixels that are too small for the classic Solex.

Thanks! Yes, the pixels will be rather large, but I‘m perfectly happy with not ideal results in the beginning. I guess the learning curve will be rather steep anyway, so I will not get the best images right away

[thesmiths]

Yes, the pixels will be rather large, but I‘m perfectly happy with not ideal results in the beginning. I guess the learning curve will be rather steep anyway so I will not get the best images right away.

There is a big learning curve how to just capture and create any image with an SHG. I think Richard had the right approach in learning on the Solex before deciding to commit to a larger project. I should add that I think a high-resolution SHG should be built around a specific telescope, so I would always decide on that first. Something around 4-inch aperture seems to be ideal and I would discourage anything longer than 800mm focal length.

[SunRick]

Hi Rick,

incredible instrument and incredible results!
Seeing your images makes me want to follow up on getting my own SHG.
While I do get jealous of your resolution, I guess starting with a Sol'Ex makes more sense instead of building my own? I have an older Orion Shorttube 80 (f/5) scope and a ASI174MM which I could readily use. Any other scope / camera I would have to buy in addition to the SHG.

I'm looking forward to seeing your pictures! Have you ever tried to make a dopplergram or even a magnetogram? Or to image HeI?

Cheers,
Jan

Thanks Jan,

As Doug Smith said, starting with the Sol'Ex really helped me a lot.....not just in the process of creating spectroheliograms......but also understanding the concepts behind the instrument. I also read up on the history of spectroheliographs from over 100 years ago (such as at Meudon) and looked at their pioneering images.
With my Sol'Ex, I also used an 80mm f/5 Orion scope, but stopped it down to 70mm. There are great tutorial videos that show exactly how to set it up and exactly how to use it. Unlike Doug's custom-built quartz slits, the Sol'Ex slit needs to be protected from focused solar heat. They suggest putting a neutral density filter over the aperture.....but don't do that. You will need an extension tube between your scope and Sol'Ex.....so just thread a neutral density filter on the extension tube where the sun is not focused. The images you can get with the Sol'Ex may satisfy you. They are not bad at all (see one of my Sol'Ex images earlier in this thread). I used an ASI178mm camera because I had one already. Even if the pixels are not matched well, it will work fine (as will the 174mm). You really want to assemble and adjust it, and leave it all assembled.
To get a lot better resolution, you need to build an SHG with a bigger scope. Like Doug said.....something around 4 inches and around f/7 is a sweet spot. It is a significant project, because you need to dedicate the scope to the SHG assembly. But, setting up all the component subassemblies, as I have described earlier in this thread, is much easier if you first have the understanding you get from the Sol'Ex. Even so, I still had to ask Doug a lot of questions!
Of course, I must say there is a great deal of satisfaction in building a high resolution SHG from scratch.....that actually reliably works the way it is supposed to. It is really cool!

And, yes, I have made a dopplergram, but not a magnetogram. Using the pixel shift feature in the software also allows you to make blue and red shifted images from the same scans.

Rick

[SunRick]

Today, I was able to image a pretty active sun in h-alpha with the spectroheliograph. I thought I would get a bad image, because I was not able to record spectral line scans until 3:30 in the afternoon. That's a bad time for my solar imaging. Unlike morning, the sun was directly above the hot house shingles from where I image, and even vultures were gliding on thermals in a nearby field. All bad signs.
But, it was cloudy in the morning during the "best" time. So, after mowing the lawn, I decided to set up for the heck of it......as the clouds had partially cleared.

Well, I was surprised. The results were better than I thought they would be! Not as good as my best images.....but certainly presentable!

Rick

5/16/2024 102mm f/7 spectroheliograph, h-alpha

Sun 5-16-24 new SHG h-alpha.jpg (2.33 MiB) Viewed 544 times

[rsfoto]

Hi,

That is an incredible image

[SunRick]

Here is the sun in h-alpha and calcium-H from my spectroheliograph today in very good seeing. This is more typical of my summer morning seeing in Kentucky.....and these calm mornings, with the jet stream winds at 0 - 10 knots today and the scope looking over farm fields with moist grass growing, are what I have been waiting for! You can especially see the improvement in the calcium-H image at full resolution. Now, if the western USA and Canada can just have a light wildfire season so my skies are not overwhelmed by high-altitude smoke......that would be perfect for this peak solar year.

Sun 5-19-24 h-alpha 102mm f/7 SHG

Sun 5-19-24 new SHG h-alpha.jpg (2.27 MiB) Viewed 282 times

Sun 5-19-24 calcium-H 102mm f/7 SHG stopped to 72mm

Sun 5-19-24 new SHG calcium-H.jpg (2.53 MiB) Viewed 282 times

Rick

[thesmiths]

Here is the sun in h-alpha and calcium-H from my spectroheliograph today in very good seeing. This is more typical of my summer morning seeing in Kentucky.....and these calm mornings, with the jet stream winds at 0 - 10 knots today and the scope looking over farm fields with moist grass growing, are what I have been waiting for! You can especially see the improvement in the calcium-H image at full resolution.

Those look really great. What local time where they taken? How many frames were stacked? Did you reduce the aperture for the Ca-H?

[SunRick]

Here is the sun in h-alpha and calcium-H from my spectroheliograph today in very good seeing. This is more typical of my summer morning seeing in Kentucky.....and these calm mornings, with the jet stream winds at 0 - 10 knots today and the scope looking over farm fields with moist grass growing, are what I have been waiting for! You can especially see the improvement in the calcium-H image at full resolution.

Those look really great. What local time where they taken? How many frames were stacked? Did you reduce the aperture for the Ca-H?

Thanks Doug. I took them in the 9:00 to 9:30 AM local time window. In the summer here, fair-weather cumulus clouds often form around 10:30 to 11:00 AM or so, and I need to beat that! I can record about 24 frames in 6 minutes......and I stacked 20 this time. Same with Calcium. I looked at each image before stacking, and they all looked sharp, so I could stack more. I deleted a couple of the 24 frames because they had recording glitches, and used Autostakkert and IMPPG for processing. I can try stacking fewer from a shorter recording period if you think that would help (due to solar features moving). The gain was only set at 10 for h-alpha (but 80 for calcium) at 16X, so each frame is not noisy.

And, yes I did stop down to 72mm for calcium-H, now that I know it makes a difference in good seeing! A friend 3-D printed an annular mask that is black on the inside and white on the outside.

Rick

[thesmiths]

I took them in the 9:00 to 9:30 AM local time window. In the summer here, fair-weather cumulus clouds often form around 10:30 to 11:00 AM or so, and I need to beat that! I can record about 24 frames in 6 minutes......and I stacked 20 this time. Same with Calcium. I looked at each image before stacking, and they all looked sharp, so I could stack more. I deleted a couple of the 24 frames because they had recording glitches, and used Autostakkert and IMPPG for processing. I can try stacking fewer from a shorter recording period if you think that would help (due to solar features moving). The gain was only set at 10 for h-alpha (but 80 for calcium) at 16X, so each frame is not noisy.

And, yes I did stop down to 72mm for calcium-H, now that I know it makes a difference in good seeing! A friend 3-D printed an annular mask that is black on the inside and white on the outside.

I found stacking 20 was just about right. It really depends on the glitches. I've figured out now how to mainly avoid camera glitches, so the main problem I have is mount scan irregularities (which I think you don't have with you AP mount). I tend to scan a little faster than you do, but not by much, maybe 18x.

I think what you're demonstrating is how really excellent seeing can be a huge benefit. I'm always looking over rooftops in London, which is probably not the best. Your grassy landscape looks much more ideal. In my case, I think the best imaging is closer to 8am local time, just as the Sun rises over the trees (and rooftops).

[SunRick]

I took them in the 9:00 to 9:30 AM local time window. In the summer here, fair-weather cumulus clouds often form around 10:30 to 11:00 AM or so, and I need to beat that! I can record about 24 frames in 6 minutes......and I stacked 20 this time. Same with Calcium. I looked at each image before stacking, and they all looked sharp, so I could stack more. I deleted a couple of the 24 frames because they had recording glitches, and used Autostakkert and IMPPG for processing. I can try stacking fewer from a shorter recording period if you think that would help (due to solar features moving). The gain was only set at 10 for h-alpha (but 80 for calcium) at 16X, so each frame is not noisy.

And, yes I did stop down to 72mm for calcium-H, now that I know it makes a difference in good seeing! A friend 3-D printed an annular mask that is black on the inside and white on the outside.

I found stacking 20 was just about right. It really depends on the glitches. I've figured out now how to mainly avoid camera glitches, so the main problem I have is mount scan irregularities (which I think you don't have with you AP mount). I tend to scan a little faster than you do, but not by much, maybe 18x.

I think what you're demonstrating is how really excellent seeing can be a huge benefit. I'm always looking over rooftops in London, which is probably not the best. Your grassy landscape looks much more ideal. In my case, I think the best imaging is closer to 8am local time, just as the Sun rises over the trees (and rooftops).

In the summer mornings here in the southeastern USA, the lawn behind my house and bordering farm fields I overlook while imaging are just drenched in dew. The solar energy for the first few hours is spent evaporating dew instead of heating the ground. That may give me an extra hour in the morning to image in good seeing. And, I am retired, so I might just want to sleep in a little!
Now, all you need is a nice place in the English countryside to avoid all those buildings! You do such a great job despite them.

Rick

[SunRick]

Sorry, I just have to post SHG images from today in really good seeing again. I don't want to post all the time! The jet stream was nearly calm again plus calm to light wind at the surface. I hope the rest of the summer is like this.....but I know it won't be.

Here is the jet stream over the USA at 8:00 AM local time (an hour before I imaged). My location is the pink "X".

Jet stream just before imaging today

Jet Stream 5-20-24 8 AM local time.jpg (611.29 KiB) Viewed 177 times

Once again, the calcium-H image (stopped to 72mm) really showed the most difference with this good seeing. I like how the long filament at bottom showed up nicely in calcium-H. You don't see that in etalon calcium images. At full resolution, even tiny features are seen. And, the h-alpha image looked very detailed too.

SHG calcium-H image 5-20-24

Sun 5-20-24 new SHG calcium--H.jpg (2.55 MiB) Viewed 177 times

SHG h-alpha image 5-20-24

Sun 5-20-24 new SHG h-alpha.jpg (2.36 MiB) Viewed 177 times

Just TheSmiths, Autostakkert, and IMPPG for processing. No Photoshop or PixInsight.

Rick

[Montana]

Interesting how the southern filament is barely noticeable in Halpha, but so prominent in CaH

Alexandra

[SunRick]

Interesting how the southern filament is barely noticeable in Halpha, but so prominent in CaH

Alexandra

Hi Alexandra,

I thought that was cool too! I wonder why that is?

Rick

[SunRick]

Here is the last SHG h-alpha and calcium-H image set for at least a week (as the weather forecast is bad for the next week) taken yesterday (5/21/24). I am still amazed that recording good hi-res SHG images is easier than I thought it would be. I planetary-image and deep-sky image too....and I think the difficulty of SHG imaging is on par with planetary and easier than deep-sky imaging. The trickiest part is constructing, setting up, and calibrating the SHG initially. But once that is done, you just plunk the unit on your mount, find the sun, find the spectral line of interest, tweak the camera lens and scope focus, and start taking scan movies.

This should be a more popular way to image the sun. I think the reason it is not is because you cannot buy larger units already set up from a supplier. As a comparison, you can buy a solar imaging scope and CMOS planetary camera....and connect them together to take good images. It is intuitive to put a camera on the end of a scope to record an image. It makes sense. Heck, I do it with a Quark/Lunt double-stack Frankenfilter on my 127mm scope at 5,100 mm focal length. However, creating a solar image with an SHG is not initially intuitive.

Describing it to an uninitiated astro-enthusiast goes like this: Aim your scope at the sun and focus it on a narrow slit and then through the back end of a camera lens to a diffraction grating and back through an angled camera lens to the camera. Huh? Then, take movies of a spectral line as you are slewing the scope. What?? Then, run the movie through magic software to create a solar image from your scan line video. Umm???

So, as a result, folks don't want to go there. It sounds intimidating. Instead they just buy an expensive, smaller aperture, etalon scope and stick a camera on the end. It's more intuitive. But, no etalon scope can match the ultra-narrow bandpass, full-disk, high resolution, multi-wavelength versatility of an SHG. Especially SHG calcium images are almost unrecognizable compared to etalon scope calcium images due to the narrow bandpass.

I encourage more folks to take the leap and build your own SHG based on a 4-inch f/7 scope. I can help, and I know Doug Smith can help. I assure you, you will have the coolest instrument in your astronomy club!

SHG h-alpha 102mm f/7 (5/21/24)

Sun 5-21-24 new SHG h-alpha.jpg (2.43 MiB) Viewed 31 times

SHG Calcium-H 102mm f/7 stopped to 72mm (5/21/24)

Sun 5-21-24 new SHG calcium-H.jpg (2.44 MiB) Viewed 31 times

Rick

[Montana]

If we could all get images as fabulous as yours then we would all be doing it however, I have watched even the most competent of solar tinkerers struggle with an SHG (Rainer and Pedro) so I think little me would have no hope of ever achieving such nirvana I am afraid I can only live and dream,
and enjoy your wonderful images


Alexandra