My solar imaging setup has a quite high magnification. Even though I use a 20 Megapixel QHY183 camera, I may only frame less than a third of the disk diameter at once. This is really neat for prominences and sunspots. But I may not record the whole solar disk. Therefore my only way to go is a panorama or mosaic.
The tricky part of recording a mosaic of the sun is, that you don’t have too much time to complete. First, the sun rotates (even the 25 days period may cause defects at high resolution imaging). Second, some features like granulation or prominences may change within minutes. For high quality results, the lucky imaging approach has to be used. Meaning, each individual recording for a tile should consist of as many images (lets call them frames, as the data is recorded as a video) as possible. In post processing, only the best frames will be selected and combined for low noise results.
Last weekend I ran the first real test for a giant mosaic image of the sun in H-alpha. I recorded each individual tile with SharpCap. I had to use the seeing filter due to a rather slow USB connected drive. Each tile consists of a set of only 100 out of 2000. From these 100 selected images, only 4 were used to create the final image tiles (which proofed to be a wrong decision, as noise levels remained quite high).
To record the complete surface, I needed to capture 12 tiles. So I ended up using 48 individual frames out of 24.000. After crunching through the 30+GB of data recorded on disk (which was only 5% of the images captured) for several hours, I finally have a stunning picture of the sun in high resolution 🙂
Processing steps: 1) Stacking in AutoStakkert!3 2) Stitching in Photoshop (manually, as neither Photoshop, nor Hugin were able to align the tiles) 3) Gradient removal in Photoshop 4) Wavelet sharpening in PixInsight 5) Histogram optimization in PixInsight 6) Cleaning of edges and border of image in Photoshop 7) Colorization in Photoshop
Finally it seems, that the Sun is waking up after a long period of nearly spotless months! This is a compiled image out of 2000 raw frames. Image is wavelet sharpened in Registax. Further sharpening, level adjustment and colorizing done in Photoshop.
This prominence occured right after the sunspot region 12579 vanished and rotated out of view. The video shows the development from 09:02:25-12:15:05 UTC+2. Video recorded with 715mm f/7 refractor with 4x telecentric system and SolarSpectrum 0.5A filter on ZWO120MM-S camera. Sequence consists of 490 images. Each image is a stack of 500 frames each. (For the complete sequence, 245.000 images have been processed)
I had the chance to borrow a Hydrogen alpha filter for solar observation. As the weather was just perfect, I set up my 80/600 refractor with the filter and a camera attached. Every 15 seconds I captured 400 frames for later processing. After 4 hours, my hard disk was loaded with 850GB of data…
Now, more than 2 days of stacking, aligning, optimizing, … are over. The resulting image sequence is simply fascinating and beautiful:
Today Mercury set its path in front of the sun. The tiny black spot was a nice view to observe. As I was in the office that day, I used a tripod, 1000mm lens and a wired remote trigger to capture a few impressions of the event:
I questioned myself whether it would be possible to enhance images of the sun using deep sky H-alpha filters. Most likely a filter with 7nm bandwidth would not show prominences. Prominences are so dim, that the rather wide bandwith of the deep sky filter passes too much of bright light to see them. Keep in mind, that typical solar H-alpha filters are in the range of 0.3-1.5 Angstrom, which is 100 times more narrow than the deep sky filter (7nm = 70 Angstrom). But who knows – perhaps the granulation becomes visible or at least the surface texture may improve…
ATTENTION: Never ever look direct at the sun! You risk your eye-sight, especially through optical instruments without proper equippment! I use specialized filters, suitable for solar work
I think, the result speaks for itself! It is an significant improvement, as the surface texture is no longer flat!
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