We haven't had a whole lot of clear nights here lately, so I have been trying to squeeze in some partial-nights of imaging when I can. Unfortunately, the right ascension motor on my Celestron CGE Pro mount, the one I use for my science rig (for taking variable star and exoplanet transit data), has died. So there will be a bit of a break in the science-data-taking while I get another rig set up. After a talk I gave recently for the AAVSO 2020 webinar series, member Gary Walker, one of the leaders of the Instrumentation & Equipment section, offered to pass along to me a Celestron AVX mount as well as an older QSI 583 CCD camera. I'm very excited to receive both! The QSI camera should perform much better than the Orion Deep Space Monochrome Imager II I've been using on the science rig. My Celestron AVX can't quite handle the 8" Newtonian I use on the science rig, but I think I got one that's on the lower end of their manufacturing tolerance -- I've seen people do better with their AVX's. So I'm hoping perhaps his will perform better and I can use the Newt with it. Regardless, it will be put to good use -- I've always got some kind of plan rolling around in my mind. :D
Meanwhile, the plethora of planets in the evening sky has been taunting me for weeks! Normally I would set up my outreach rig and do some planetary imaging -- my 8" Celestron Schmidt-Cassegrain on my Celestron NexStar SE mount. However, since I gave up on using my 11" SCT, I've been using the 8" all summer, and plan to keep it on my main imaging rig throughout the winter. So I decided to spend a few evenings on the planets, and I swapped out my deep sky optics train for the planetary one.
For deep sky imaging, I use a 0.63x focal reducer/field flattener on the C8 to decrease the focal ratio from f/10 to f/6.3 (making the scope "faster") while widening the field of view. The reducer puts me at an effective focal length of 1280mm, which gives me a large enough field of view to image most nebulae (except for the very largest ones), but not so large that I can't do galaxies and planetary nebulae. However, for getting the best resolution on solar system objects, you want a looooooong focal length -- as much magnification as you can get away with given the aperture of your scope and the seeing conditions. I previously used a Celestron 2x Barlow, but always got a bit of chromatic aberration from it, so I finally upgraded to a Baader Hyperion 2.25x earlier this year, and finally gave myself a chance to use it. So I swapped out the focal reducer for the Barlow, and I also took off my PrimaLuce Esatto focuser because the last time I tried this, I had some trouble with it being too close to the scope and hitting the focuser knob.
First up: Jupiter
We also have a nice view of the Great Read Spot here. The GRS is a massive storm that has existed for at least the past 360 years, when it was first observed. Within the cyclone, windspeeds can reach 268 miles per hour -- much higher than Earth's hurricanes. The storm is 1.3 times the diameter of the Earth!
No gas cloud details for me -- it's just too small! At only 2.3 arcsec across, that's only 13 pixels wide at my pixel scale. But still, it's a bluish-green disk, woot! (Actually the camera didn't capture the color that well for this one -- I think it was too small to do the color calibration correctly. So I took a guess based on what I've seen in the eyepiece. It's not really right at all).
Visible at the bottom of the planet is the southern polar ice cap, which is a combination of carbon dioxide ice and water ice. The darker areas have less of the red dust, which is why they appear darker.
I managed to get a fair amount of detail -- not the most I've seen from other imagers, but still cool! I'll need to keep an eye on the seeing forecasts and give it another go here in the near future.
And finally, Uranus
- Open the video for each filter in AutoStakkert; auto-place appropriately-sized APs, and then stack the best 20% of frames. (I have RGB Align ticked so that it aligns the next video to the last.)
- Open the stacked images in RegiStax and adjust the wavelets. I prefer to do that in Linear mode -- I've gotten much better results with it.
- Bring the wavelet-deconvolved images into PixInsight, convert to grayscale (RegiStax likes to save TIFs in RGB), and apply LinearFit to bring each color channel to about the same level (picking one of the filters as the reference).
- Combine the three color channels using ChannelCombination
- Correct the color using ColorCalibration, with the whole image used as white reference and a preview box of the background as the background reference. (I have found this works very well for Mars, Jupiter, and Saturn.)
- Tweak saturation and the brightness curve with CurveTransformation
- Use MultiscaleLinearTransform to do a little more shaprening
- Use MultiscaleLinearTransform again to blur the 1-pixel level, since some weird pixelated hatching tends to result from RegiStax's wavelet deconvolution that looks like debayering when it's not
- Bring finished image into Photoshop to resize (I shoot my videos cropped to a small window size, usually 640x480, to speed up acquisition & processing and reduce file size). I usually change the DPI from 72 to 300, and then drop the auto-upscaled size from 450% to like 200-300%, and then do some denoising in Camera Raw Filter as needed. (This is mainly so that my watermark doesn't look super pixlated when the image gets blown up online).