Sol in H⍺- 29 July 2021 - A bit of experimenting.

[Hughsie]

I recently purchased the Solar Astronomy book published by Axilone Astronomy and it has encouraged me to look at image acquisition and processing somewhat differently to what I have been doing so far. Admittedly there are still a lot of information to go through, however, it is a great read and well worth the investment based on what i have read through so far.

For image acquisition I use the ZWO ASI174mm camera and to date I have been adjusting exposure/gain to fill 60-70% of the histogram. Seems I have been missing a trick and with the images below I pushed this to 80% to hopefully improve SNR (in recent days I have gone further to 90%). I have also been somewhat ‘hung up’ on FPS and have kept to using Mono8 to avoid the drop off in frame rate when using Mono16 despite it offering a higher dynamic range.

Also, the combination of scope/camera pixel size and Barlow lenses suggested that with a 2.5x and 3x Barlow I would be achieving a good resolution with decent seeing, however, when using the 5x Powermate there would be significant oversampling. A few weeks back I attempted image acquisition with a 5x Powermate and adjusted the camera settings to Bin 2x2 without much success but the seeing wasn’t great either. The 29th July offered a steady sky and so not wanting to be deterred I tried Bin 2x2 again. 

Here is what was thrown out.....

Images 1 & 2 - Prominence on the North East Limb. Here Mono16 was used and I pushed the histogram to 80% which allowed me to capture both the prominences (even though they were barely visible when live on my lap top screen) and the Chromosphere. I know others have done this before but I have avoided doing this, preferring to capture the proms separately by significantly raising the camera gain. After seeing the results I am happy to change! 40% of 1,000 images stacked. Exposure time 10.7 ms, Gain = 100. Altair Astro 3x Barlow used. Bin 1x1.

      

 

Images 3 & 4 - Moving across to the South West Limb we have some more prominences. Again the same approach as Images 1 & 2 was adopted using the same exposure time, Gain and Barlow. I just need to sort out that bright edge of the disk.

     

 

Image 5 - AR12847. Mono16 used and Bin 1x1. Exposure time was 21ms with Gain set at 150. This was difficult to process and noise was difficult to control. 5x Powermate was used. 

 

Image 6 - Again AR12847 captured a few minutes later. Exposure time 20 ms, Gain 150. Mono16 and Bin 2x2 used. I was able to push the sharpening of the image a bit further without a significant increase in noise. The image size has also been scaled up slightly to match the size of Image 5.

 

What do you think?

 

John

[vineyard]

Very nice - I particularly like image 3.

I use Mono16 and just ignore FPS (my laptop is an old one w USB2 anyway so it wouldn't make much difference!).  I've never really looked at how much of the histogram is being filled, judging it more by eye on the laptop screen - I should probably be more systematic.

I'm most intrigued by the gain 100 - I tend to keep gain to 0 (ASI290MM) - may experiment w higher gain next time to see what difference it makes.

Wrt barlows, I did try 2.5x PM once but I found the image a bit softer than just using ROI w/o barlow - w hindsight I should have binned 2x2.

Cheers!

[Kitsunegari]

200-300 frames total, subtract 90% and stack 10.   Thats all i do.

[Chris-h]

Beautiful images. I always use 80% histogram to capture both surface and bright proms.