Saturn and Overcompensating

Saturn at 1600 ISO and 1/60 exposure, from 60fps HD video.

August 9th, 2019, 11:20 p.m. local time

This evening I tried out my new camera on both Jupiter and Saturn.  I logged the experience with Jupiter here.  I will now discuss the session afterward with Saturn.

As with Jupiter, I relied on all of my past experiences for the preliminary camera settings, specifically for ISO and exposure.  In general my “go to” Saturn settings have been ISO 1600 and 1/60s exposure.

I took four sets of four videos each.  After each set, I always refocus the telescope.  Focus is really the most important variable in any of my planetary imaging sessions.  It is difficult to fine-tune focus, as it is difficult to tell how good the focus is on the camera’s LCD screen (and not to mention the object is constantly moving since I don’t use a tracking mount).  These objects are hundreds of millions of miles away; it’s remarkable we can focus in on them at all!

So the first image was “standard” and its post-processing results are at the top of this post.  As with Jupiter, I feel the final image is on-par with the best my old camera could produce.

When I refocus between video sets, I always bump up the ISO setting significantly, as this makes it much easier to locate the planet/object when manually repositioning the telescope tube.  By my own convention, I go to picture mode and use ISO 12800, which exposes a very bright dot for both Jupiter and Saturn.

I noticed on my new camera that video mode is now able to capture with ISO 12800 (the old Canon EOS Rebel SL1 could not).  Just for fun, for the second video set only, I left the ISO setting at 12800 and then took four videos.

As expected, the final, raw image looked very over-exposed.  It occurs to me that I have never posted a raw image after the video frames are stacked (i.e. before initial wavelet changes in Registax), normally because those raw images are not terribly interesting.  But this may be a prime opportunity so you can see a before-and-after comparison:

Raw image. Saturn at 12800 ISO and 1/30 exposure, from 60fps HD video.

I decided to put it through more post-processing than I normally would, to try to correct the curves, gamma, and filter out excess light via histograms.  I did this mostly in PaintShop Pro.  Here is the final result:

Post-processed. Saturn at 12800 ISO and 1/30 exposure, from 60fps HD video.

It doesn’t look too bad, and arguably may even be a much clearer image than at ISO 1600.  I really like how the planet turned out.  I only felt that color around the rings was a little off.  I tried a number of techniques but couldn’t get rid of the red/blue/green splitting that you can still see.

My takeaway is that I plan to try slightly higher ISO settings for both Jupiter and Saturn on my next attempts.  I’m thinking ISO 3200 and 6400.  This may require tweaks to the exposure as well.  I’ll be back to my original methods of logging settings in my journal after every refocus.

Summary of my equipment, settings, and software used:

  • Telescope: Dobsonian reflector 254mm / 10″ (homemade)
  • Camera: Canon EOS Rebel SL3
  • Barlow: TeleVue Powermate x5 1.25″
  • Filter: Baader Neodymium 1.25″
  • Canon T ring and adapter
  • Relevant camera settings:
    • ISO 1600 and 12800
    • Exposure: 1/60 and 1/30
    • HD video at 60fps
    • Created from multiple videos of about 25s each, best 60% of frames
  • Software for post-processing:
    • PIPP
    • Autostakkert
    • Registax 6
    • PaintShop Pro for final minor touchups

6 thoughts on “Saturn and Overcompensating

  1. I find Jupiter the easiest to focus on because I will focus on the moons. Saturn needs more tweaking and your method of shoot – focus – shoot – focus – shoot… works best for me too.

    If only auto-focus worked in astro-imaging!

    Liked by 1 person

    • Thanks for mentioning this, as I thought about bringing it up in hindsight. Yes when I am focusing Jupiter, I ignore the planet and try to get the moons as pinpoint as I can. Saturn is far more difficult but sometimes there is a stray star or Titan to latch on to.

      Like

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