Second light with Double Stack
My target has been to be able to capture prominences and the solar surface with a single exposure. As you will have seen from my previous images, it is possible, but at the expense of a lot of work, strong stretches, and in the end, the contrast that is possible is limited. As I mentioned before, looking to double stack (DS), it appears that Lunt 60 DS unit is not currently available?  But I was surprised to see, at half the cost, the Lunt 50 DS unit works well with the Lunt 60, no adapter required. Not being the most patient person, I opted for the Lunt 50 DS unit. And I know now my seeing is rarely great, so I would loose nothing in going to a slightly smaller aperture. For my first light, I was blown away by the difference in contrast, shown here.

Seeing was not great for my first light, and it was way to windy, and had many clouds pass through. But enough to show proof of concept for Double Stacking. This time seeing started out well, slightly above average, with no wind, but then seeing went on a rampage, so I had to cut this animation at 25 minutes, seeing was just so bad. But at least for 1/2 hour I got a better look at the performance in double stacking. 

Also, in my First Light, I had a strong reflection of the Sun, which was hard to suppress. This time round I realized that the DS filter had more adjustment, it must have been sticky the first time out. So the reflection turned out not to be an issue this time.

About the image
The most remarkable sighting was a bright flare (which looks black in this inverted mode). It is on the lower left of the image and only shows up in the last frame of this video. I did record more frames later under horrible seeing, so I can tell you the flare lasted only about 40 minutes. There are a number of really interesting prominences, but the ones I like the best is the group on the left limb.

Capture and Animation Steps
My animation used brightness inversion on the solar disk, thus both prominences on the limb and surface (the latter are called filaments) will appear bright, as will surface sunspots. Seeing was just average for the frames I show, and there was variable haze/transparency during the capture. But I learn something every time I image, so this is another learning experience.

This video of 13 frames was created from images taken on November 5 over  25 minutes. The individual frames of the animation were all from 60 second SER videos at 2600x2600 pixels in 16 bit mono (the camera is 14 bit) taken at 23  fps. Each video was separated by a delay of 75 seconds. The resulting 1350 frames were stacked in Autostakkert3 as the best 15%, so about 270 frames were used in each of the final animation frames.

Processing in ImPPG
Nearly all of my processing of the AutoStakkert stack is now in ImPPG. First I do a batch image align for each video frame, using the solar limb. I previously aligned in Photoshop, but that can freeze the prominences, so much better to do a limb align. Then I do a processing curve that brings out the prominences, while inverting the surface features. This includes a WP and BP balance so all the frames have similar overall brightness. I also do a deconvolution (2 px, 500 iterations), and two unsharp masks (one enhancing at 8.7 px at 1.15 and one for noise reduction  with 0.93 px at 0.19).

Final contrast and color adjustments, as well as the gif animation, were done in Photoshop. 

My Layman’s guide to the “Top 10 things to see in Solar Ha.”
This guide continues to be very popular, and it appears many have not yet seen it, so for those that missed my previous posts, I’m including again my list of the Top 10 things to see in Solar Ha. Our Sun in Ha has so many interesting features that it challenging to understand exactly what one is seeing.  I compiled this summary of as a viewing aid for myself, hopefully you may find it useful too.

In white light we only see the Sun’s 6000 Kelvin photosphere “landscape”, consisting of:
•    Darker, cooler sunspots
•    Granulation, consisting of hotter and brighter rising; and cooler and darker sinking convention cells, like boiling porridge.
•    Faculae, bright hot patches of concentrated magnetic flux.

It is the chromosphere that shows up In Ha, as we block out the Photosphere’s overwhelming white light. The chromosphere is a much hotter, 2000 km thick layer, lying above the Photosphere. With temperatures rising to 17000 K, the chromosphere efficiently excites hydrogen to produce Ha emission. 

The chromosphere shows a very different “landscape” than the Photosphere:
•    Spicules, tiny bright spikes, form a 3,000-10,000 km layer of bright fuzz on the Sun’s limb, and darker spikes on the solar disk. They are dark on the disk as they are cooler than the chromosphere below them. Few last more than 15 min, but the Sun has 100s of thousands of them at any one time.
•    Fibrils are tiny low contrast darker filament-like structures. 
•    Dark Mottles, comprised of fibrils and spicules, blanket the entire disk. 
•    Field Transition Arches are groups of longer fibrils that join areas of opposite magnetic polarity.
•    Prominences loop out from the limb: these are glowing, but cooler, hydrogen gas lifted from the Sun by magnetic fields. Prominences rise 100s of thousands of km above the hotter chromosphere.
•    Filaments are the darker clouds that seem to float on the solar disk. Filaments are prominences, appearing darker because they are cooler and higher, extending above the hotter chromosphere below them.
•    Plage (French for beach) are irregular, bright patches on the solar disk, found around active regions. They mark nearly vertical emerging or reconnecting magnetic fields and can last several days.
•    Ellerman bombs (named for the astronomer who studied them) are tiny, brighter spots that fluctuate in brightness, associated with large plage.
•    Flares show a brightening within a sunspot group, often with a “comb-like” flow.  They last from a few minutes to hours and change in both intensity and area as you watch.
•    Sunspot umbrae are the dark cores of sunspots, much like what is seen in white light. However, sunspot penumbrae branch out into whirls consisting of fibrils and spicules. 

Bonus, not in the Top 10, because it is difficult to observe:
•    The Chromospheric Network is outlined by filigree, which are very tiny bright spots that are less than 1 arc-second in size, and best observed off-band of Ha.

Note that it is common to invert light and dark on the solar surface, which provides improved contrast for the solar disk, and a better brightness match to the fainter prominences. It also has the advantage that the otherwise dark filaments on the surface (which are prominences) are now bright, matching the bright prominences at the limb.