It’s September 2022 and the planets are back! Well, at least at a reasonable hour. I posted a Jupiter image in the previous blog entry but I was up pretty late to catch that. Saturn is high in the sky at around 11:00 PM now, with Jupiter a couple of hours behind, and Mars after that. The major planets will be better observed in the fall this year – and considerably higher in the sky than last year. So, that’s less atmosphere to cut through. It should be a good fall for planets.
But anyway, on August 27th we had another night of good “seeing” from our valley location, and I couldn’t stop myself taking sequences of Saturn. I used my little ZWO ASI120MC-S camera that I usually reserve only for auto guiding, and plopped it onto the back of the telescope through a Televue 2.5x Powermate expander. There’s nothing special about this camera, it’s pretty low-end. But it can capture fast video sequences over a USB 3.0 port to my MacBook Pro laptop. The Powermate gave me more magnification to fill up those 3.75 µm pixels. The planets are bright, but they’re pretty small through the telescope compared to say – a galaxy.
I processed one of the sequences into my best Saturn shot yet using Siril and finally, to do the wavelet sharpening. I was pretty happy with the shot – until I showed my friend Roman the results. Roman had been playing with ON1 NoNoise AI noise reduction software, and put the finishing touches on it to produce this result:
Thanks Roman! In any case, this neophyte astronomer is getting better at processing video sequences into images. My original result is below after a couple of hours of hacking around with it in Siril. Still, I was happy with this. The Cassini division in the rings is unmistakable as are various cloud features.
The process is to take a high frame-rate video, not a still image, with the hopes that a small percentage of the frames will be lucky enough to find a quick slot of steady air through which a stable image can be obtained.
The Siril software then automatically weeds out those best frames. (Manually poring through all the frames wouldn’t be fun!) I chose to take the best 3% out of nearly 4000 frames acquired at 50 frames per second and over a three minute period. That’s 20 milliseconds of exposure per frame and about 120 good frames. Unlike deep sky photography, you can get away with short exposures because the planets are so bright. Even with my f-10 telescope; even with the 2.5x expander bringing that up to f-25! If you ever strove to obtain a decent f-1.8 lens, you’ll see the irony of that statement. Aligning and averaging together (stacking) those frames gives a starting point for sharpening the image.
The image below is my result of processing in Siril:
And here, is a 100-frame portion of the total 4000 frame video. Not necessarily the best 100 frames, just a selection somewhere near the middle of the sequence. This shows what we’ve got to work with. Yet even in this 100 frame slice, there are times of relative stability. And there are certainly many nights when atmospheric conditions would render just a jumbled mess: