Sunday, May 27, 2018

#141 - Thursday, May 24, 2018 - Finally, some good atmosphere

Having excellent atmospheric conditions is important to getting sharp, clear images of solar system bodies.  This is not terribly common at my home location, but ClearSky promised 4/5 "seeing," a term used for how stable the air is (bad seeing results in the swirling mushiness that makes it hard to see fine detail on planets or the moon), and the forecast delivered!

I set up my 8-inch Schmidt-Cassegrain in the front yard on my Celestron NexStar SE mount.  I test how good the seeing and transparency are by stepping up magnification bit by bit.  I align the mount using a 25mm eyepiece, and then I slewed over to Jupiter and put in a 17mm, 13mm, and then finally a 6mm eyepiece.  Usually, when I look through a 6mm eyepiece (which provides 333x magnification on my C8), Jupiter just becomes a fuzzy ball.  But when the conditions are good, I can resolve a few cloud bands!  So I went ahead and attached my ZWO ASI1600MM Pro camera, the five-position filter wheel I have my LRGB filters in, and then I connected the camera to my tablet, which I had on a folding table to the side.  Once I got it centered and the exposure time turned down, and the telescope focused, I cut the ROI (region of interest) down from the full resolution of 4656x3520 down to 800x600, which effectively "zooms in."  I could use a Barlow to increase magnification, but the native resolution is already 0.4 arsec/pixel, and even a night of really good seeing isn't going to get that low, since the atmosphere always has a slight blurring effect.  Using a Barlow would also double the focal ratio, taking it from f/10 to f/20, which would mean I'd need to increase my exposure time, which would reduce my frame rate.  One of the big bonuses of using a ROI is the increase in frame rate, since the camera only has to read off part of the chip.  I was pulling 30+ fps, sometimes as high as 60 fps.  At high frame rates, you can grab more frames in the clear moments of seeing, which gets you a larger number of high-quality frames to stack in RegiStax later.  So it's a good deal all around.
I use SharpCap with my ZWO camera to capture solar system objects.  I've used FireCapture in the past, but it sometimes has really weird behavior, and I find it more difficult to use, especially on a tablet, since the buttons are so minuscule.

The seeing degraded later in the evening when Jupiter and the Moon moved over top of my apartment building, since the roof was probably emitting a lot of heat from the day.  The Great Red Spot was in a better position later in the evening, but the earlier image came out better.  Both are still awesome though!
Date: 24 May 2018
Object: Jupiter
Camera: ZWO ASI1600MM Pro
Telescope: Celestron C8
Accessories: Astronomik LRGB Type 2c 1.25" filters
Mount: Celestron NexStar SE
Frames: L: 1186/3010
R: 945/3002 
G: 951/3008
B: 668/3002
Exposure: L: 12 ms
  R: 20 ms
  G: 20 ms
  B: 25 ms
ISO/Gain: 139
Stacking program: RegiStax 6

Date: 24 May 2018
Object: Jupiter
Camera: ZWO ASI1600MM Pro
Telescope: Celestron C8
Accessories: Astronomik LRGB Type 2c 1.25" filters
Mount: Celestron NexStar SE
Frames: L: 1054/3002
R: 1336/3006
G: 827/3006
B: 994/3006
Exposure: L: 10 ms
  R: 20 ms
  G: 20 ms
  B: 25 ms
ISO/Gain: 139
Stacking program: RegiStax 6

The lunar images came out great too!  
Date: 24 May 2018
Object: Moon
Camera: ZWO ASI1600MM Pro
Telescope: Celestron C8
Accessories: Astronomik L Type 2c 1.25" filter
Mount: Celestron NexStar SE
Frames: 496/3010
Exposure: 5 ms
ISO/Gain: 139
Stacking program: RegiStax 6

Date: 24 May 2018
Object: Moon
Camera: ZWO ASI1600MM Pro
Telescope: Celestron C8
Accessories: Astronomik L Type 2c 1.25" filter
Mount: Celestron NexStar SE
Frames: 330/3013
Exposure: 7 ms
ISO/Gain: 139
Stacking program: RegiStax 6

It was a great evening!

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