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// kstars · dark library

Building a dark library in Ekos

A dark library is a set of master dark frames that Ekos applies automatically during autofocus and alignment, so its star detection and HFR measurements stay clean. To be clear up front: this is not for stacking your final images — for that you'd shoot dedicated darks. Once the stack is installed, this is the process I use to build a library per camera, demonstrated end-to-end in the video below.

The process, step by step

  1. Set a dark night. Start KStars and move the simulated clock to a dark, moonless window — I use September 21st, just after 11 PM — so the scene matches the conditions you'd actually image under.
  2. Build an Ekos profile. Open Ekos and add your camera drivers (here, the Touptek drivers). A profile needs at least a telescope and a camera; I also add the filter wheel — both to confirm the driver talks correctly and to switch filters within a sequence later.
  3. Connect. Save the profile, start the INDI server, and connect the devices — wait for everything to come up green.
  4. Know what it's for. This library isn't for stacking. Ekos uses it during autofocus and alignment, subtracting a matching dark from each frame so HFR readings and the plate solver work on clean data.
  5. Configure the optical trains. In the primary optical train select your main camera — my mono ATR533M. In the secondary optical train select your guide camera. Separate trains let Ekos build and pick the right darks for each camera on its own.
  6. Capture the main-camera darks. Open the Dark Library under the Camera module, confirm the primary optical train is selected, and set a range of exposure times that's practical for autofocus and alignment (not every possible value). Press Start and let it build the master darks.
  7. Repeat for the guide camera. Switch to the secondary optical train and run it again. For guiding I never expose longer than about 3 seconds, so I cap the exposure times to that range — no point building darks I'll never use.
  8. Done. Both cameras now have master darks that Ekos applies automatically during focus and alignment. Add a camera or change gear, and you just build a fresh train and run this again.

New here? Start with the Ubuntu setup guide to get KStars/Ekos installed.