Re: Two Solstice Transits

Alan Friedman

Hi Konstantin,

Thank you for your comments and questions. 

As you’ve guessed, the image is a combination of data. The sun detail results from a stack of 300 or so sharpest frames from a video stream of 1600 frames. These 300 frames are aligned using 130 points across the disk and stacked to permit further processing than would otherwise be possible given the noise in the individual frames. The camera I use is an older Point Grey Grasshopper Xpress. It’s a 6mp sensor that can capture the full disk of the sun at 900mm, which I achieve using the f4.9 Stowaway with a 2X Powermate. This firewire camera has a maximum rate of 12 frames/second in 8 bit mode. That yields 6 frames with the ISS on a typical pass. Of these, 4 were less than optimal and one showed the ISS directly over the beautiful active region at upper right. The sixth was nice and sharp and in a quiet region of the chromosphere. The data from this frame was incorporated into the stacked data to create the final result. Likewise, the exposures for disk and prominences are different so these components are recorded separately and then combined to make the finished image.

The seeing was quite good at times but far from perfect and the wind was very strong. After setting up I had to pick up the rig and move it alongside a tree! 900mm is a forgiving focal length. The hardest part of imaging the sun over a field this wide is attaining an even hydrogen alpha band. Rotating the etalon using the dew shield of the Stowaway helps to fine tune the bandwidth and to keep the brightness even across a wide field. Hydrogen Alpha filters are a little like violins, no two play exactly the same. I’m fortunate to have gotten a sweet one that has held up well over two decades. 

Clear skies,

On Jun 23, 2022, at 3:11 AM, Konstantin von Poschinger <KPoschinger@...> wrote:

Hi Alan,

thanks for sharing this stunning images. Can you tell how you menage to get such a sharp H-Alpha sun with the ISS in a one shot image. The seeing conditions must have been absolutely superb. Or is this image a result of adding multiple images with one that has the iss in it. 
I would like to see your setup. 



Konstantin v. Poschinger

Hammerichstr. 5
22605 Hamburg

Am 23.06.2022 um 00:47 schrieb Alan Friedman <alan@...>:

Hi all,

I brought my f5 Stowaway and 400 mount about 10 miles from home yesterday for a meet-up with the sun and the ISS. It was an adventure I’ve done before - most recently on June 21, 2020, exactly two years ago. I had pretty good conditions both times.

The space station looks pretty much the same as it did two years ago. Our Sun was a different story altogether which moved me to do a comparison of the two captures side by side. Two years ago we were still in the depths of solar minimum. Yesterday the sun sported a bunch of active regions, large filaments - even a fast moving exploding prominence to welcome the 1/2 second flyby of the space station’s dragonfly silhouette.

Hope you enjoy the sunshine!

Best wishes,

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