Re: Two Solstice Transits
Hi Konstantin,toggle quoted messageShow quoted text
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.