First light with SHG-700

[cytan299]

Hi everyone,
I recently acquired an SHG-700 (https://mlastro.com/mlastro-shg) for solar imaging which I think I may be the first person in Singapore to get this. FYI, it is made in Vietnam which I think it's great to have an astro instrument made in an Asean country. For people unfamiliar with the SHG700, the idea behind it is to use a diffraction grating to isolate the H-alpha (or calcium or any other absorption line) absorption line and then by scanning it over the entire face of the Sun, its image can be reconstructed (https://solex.astrosurf.com/solex-theory-en.html). Here's a sample H-alpha image that I took on 20 Feb 2025 @ 0346 UT:

11_46_09_20250220_mix_0_00_small.jpg

As you can see, the Sun is really active right now with its prominences and filaments. I'm really impressed with the result despite having made several mistakes due to my inexperience while acquiring the data.

For those people who are interested, here's the link to my review of it on cloudynights:

https://www.cloudynights.com/topic/9554 ... he-shg700/

cytan

[yltansg]

Hi CY,

That is an impressive first light. The details on the HA full disk are amazing. Congrats!!

I find your review on cloudynights very informative. Thank you for sharing. Looking forward to more images from your SHG.

Alfred

[yltansg]

Hi CY,

That is an impressive first light. The details on the HA full disk are amazing. Congrats!!

I find your review on cloudynights very informative. Thank you for sharing.

One question - how long, do you think a first timer would need to do the required setting up (ie alignment, focusing etc) to get a good scan?

Looking forward to more images from your SHG.

Alfred

[cytan299]

Hi Alfred,
I think the major problem I have right now are clouds, dang clouds and rain. It makes it setting up and taking SER files with the SHG challenging to say the least.

Since you asked about time and because you're more experienced with Solar imaging than I am, please take what I say below about timing with a grain of salt:

• Polar alignment is critical for this method. Therefore, I start with my Thousand Oaks Solar Filter to do drift align with the Sun. The reason for doing a good PA is to minimize any drift so that this drift does not compete with my scan. Unfortunately, Daytime PA must be done because I had thought I could cheat for my second light but that was kind of a disaster
  • Besides taking about 1/2 hour to do daytime PA, everything needs to be rebalanced after switching from Solar Filter to SHG. This takes at least another 15 to 20 min of time.
  • IMO a good Polar alignment is also crucial for sync'ing the mount to the Sun. This allows me to get back to the Sun after scanning or when the dang clouds cover up the Sun. This saves me a lot of grief from getting lost.
• Both focusing and centring of the Sun onto the slit is crucial. Watch Minh's video on Focus Refinement Procedure to prepare.
  • For the first time, it'll take a little while because first you'll need to figure out how to find the Sun first to do the telescope focusing. I have marked where the focus is supposed to be now, so it's now within a few electronic focuser steps. I can imagine taking about 15 minutes to do this the first time.
  • Make sure that both RA and DEC are scanned. The first time I only scanned RA and so I had some vignetting. Not having a good PA means that the Sun can drift past the edge of the slit and cause clipping even after you've centred it. That's what happened to me the second time around.
• The first shot tells me how much tilt to correct after running the SER file through JSol'EC. I don't have a rotator at this time so have to do it by hand.
  • I have found it easiest to park the mount where the counterweight is down (Park 3 in Astro-Physics mount parlance: https://astro-physics.info/tech_support ... efined.pdf) and then put my iPhone on the flat part of the SHG. I use an app that measures tilt to help me to know how far to rotate the SHG. Once I do that I use a planetarium program to slew back to the Sun. Since I'd sync'd the mount to the Sun previously, my telescope just goes back to where the Sun is.
  • This will take another 15 minutes depending on how fast your imaging computer is for JSol'EC to do its thing and then going out to do the tilt correction.
• Getting the slew speed correct. That comes by looking at the JSol'EC output and making sure that X/Y >= 1. Undersampling X/Y < 1 is undesirable. That'll require some monkeying around as well. Probably another 15 to 20 minutes because in this month of February, clouds keep photobombing my SER file which makes the file useless.

As you can see the steps are quite involved. I can easily spend more than 1 hour setting up. It's really not like using a filter because I don't think PA is that critical here since I can always let SharpCap do its auto-centre thing. And once I've found the Sun, it's hard to lose it which unlike the SHG where I'll have to make sure I sync my mount once I've found it and then doing RA/DEC scans to be sure. Of course, I already know that the SHG technique trades Time for Space: Space in the sense that with filters, I take the entire image at once. But with the SHG, I raster scan which takes time. Since I haven't really done any serious Solar imaging with Filters, I really can't say which method is better. But I do know which method is *cheaper*

Finally, IMO, Singapore weather is just not conducive for astrophotography anything. For the SHG, it's extremely challenging because clouds keep covering up the Sun which makes it very difficult to scan, focus or take a SER file. And after 3 sessions, I can safely say that from 9 am to 11 am, I can only get between 1 to 2 good SER files!!!!! And each SER file lasts for only about 20 s. Unbelievable.

And if you're wondering why I stop at 11 am, it's because dark clouds start coming in from Malaysia and it threatens to rain or drizzle, or it's so clouded over that it becomes useless for imaging. Thank goodness I've dismantled my kit before anything got wet the first two times.

Anyway, it's just pretty neat to get Solar Images regardless of the challenges. If it's easy, anybody can do it

cytan

[yltansg]

Hi CY,

Base on what you have said, I think it is very important for me to be familiar with all the required orientation, alignment, focussing steps. I need to watchMinh's video again. Thank you very much.

Alfred

[cytan299]

Hi everyone,
Here's 3rd light. My second light wasn't that great. So after fighting clouds, I got two images, which I think are acceptable for a newbie. These were taken on 24 Feb 2025.

The first image was taken at 02:32 UTC:

10_32_53_20250224_disk_0_00_enhanced1_good_bg.jpg

and the second at 03:08 UTC:

11_08_30_20250224_disk_0_00_enhanced1_good_bg.jpg

IMO, although the SHG700 has a learning curve, I think that it's not that steep because I could get decent images after just 3 tries. I can definitely see improvements from my first image.

And here's false color images of the same data from above:

10_32_53_20250224_disk_0_00_enhanced1_good_bg_colorized.jpg

11_08_30_20250224_disk_0_00_enhanced1_good_bg_colorized.jpg

Enjoy!

cytan