Getting the most from Kstars and Ekos

automation 101

When I first started using Kstars and Ekos, I had no end of wasted nights (and it seems I am not alone from what I read online in some of the main forums) but I am pleased I perserved to iron out the wrinkles as I am now fully automated. This article discusses some tips and tricks I discovered that may help simply your journey and help you get the most from this software.

Written by Jonathan Eames
October 10, 2020

Kstars and Ekos – Dark Frames

Never use Dark frames or a master dark captured using other tools such as APT. I discovered the hard way that you must take new dark frames using Ekos to ensure dark frame subtraction in tools like PixInsight works properly.

ZWO OSC cameras and PixInsight processing

Here is an odd one that got me when moving from APT (using ASCOM) to EKOS (using INDI). If you use a ZWO OSC camera, be careful when using it with EKOS.  The ZWO SDK enables the user in the acquisition software to control settings that influence the white balance of a displayed color image. This is achieved by two parameters, WB_R and WB_B, data range 1 to 100, the default values are WB_R = 52 and WB_B = 95. The intensities of the red channel will be multiplied by WB_R/50 and the intensities of the blue channel by WB_B/50. Unfortunately the results of this multiplication are also written to disk in the FITS file. So it is important to set the values of both parameters to 50 and subsequently apply ‘Save Config‘ to persist it next time you boot up. Only in this way will the real raw intensities be saved to disk in the FITS files. Since the data coming from the camera are saved in FITS files rounding errors and clipping of high values will arise (Such a complication is generally avoided when the ASCOM camera driver is used instead of the native driver).  Failure to do this will mean your darks do not subtract the noise correctly too. See the picture below for my settings for the 294 for WB_R and WB_B.

ekos white balance

Kstars and Ekos – Initial Configuration stuff

If you are using Ekos / Kstars on a Raspberry Pi either with Astroberry or Stellarmate don’t forget some basic configuration steps worth doing on a cloudy night before you start imaging:

  • Kstars – go to “Data” on the Kstars main menu – download the visual imagery for Kstars, it may take a while but it makes a big difference. I download all the files except the very large USNO NOMAD catalogue per below:
    EKOS
  • First time you connect your main camera via INDI, check that you have set the format to Raw 16 bit and save the config. I did my first nights imaging at 8 bit by mistake, a clue was the smaller file size and inadequate image quality!!
  • Set up time and location in Kstars and Ekos and avoid guiding and alignment issues – see my separate article here.
  • Using the INDI driver for your telescope mount first time- assuming you do not have a dome, make sure you disable the “dome policy” in the INDI driver options tab otherwise you cannot unpark your mount…

Kstars and Ekos – Plate Solving for alignment

If you are using Ekos / Kstars on a Raspberry Pi you have the options of using one of two plate solving application – Astrometry or ASTAP. Depending on your telescope and setup sometime one is faster than the other. I tend to use ASTAP now as experience show me as it seems faster than Astrometry but others report the reverse, so try both!

Astrometry

This can be run in differing ways – how you configure it depends on your RPi setup and how you automate. The options are:

  1. If you connect to your RPi via VNC and run all your software on it and have WiFi connectivity issues then I highly recommend installing the astrometry index files locally on the RPi (lucky you have a 64GB sd card!) and plate solving offline on the RPi.
  2. If you connect to your RPi via a network cable or you remote into it via a Windows or Mac install of Kstars/Ekos using the INDI server across the network you can install the index files locally and choose Remote or Online to have your image uploaded and solved by Astrometry by their servers – choose an option to suit your internet connection speed – I don’t recommend online solving if connecting to the RPi by WiFi unless its a fast good connection (5G) as all images have to be downloaded locally first and then uploaded to Astrometry, it just slows everything down.

To install the index files locally on the RPi, in the Alignment module (once connected of course), click on Options and then the Index tab to bring up the Index file list. Make sure you select a directory other than “All Sources” for the Index File Location first, as this is where they will be stored , then click on the required and recommended index files to start downloading each one – this a cloudy night job as the downloads can be pretty large!

Kstars and Ekos

Full installation instructions for Astrometry can be found here and the Astrometry web site is here.

ASTAP

ASTAP is actually a multi-platform stacking program that has a very capable plate solver so can be run locally and remotely in exactly the same way as Astrometry so the local and remote connection speed rules apply equally. The good news is that ASTAP is pre-installed on Stellarmate and the Astroberry server image already.

If you run EKOS on wondows / Mac using the INDI server architecture then you will need to install ASTAP locally along with G17 Star Catalog otherwise nothing will happen. Of course the image to solve will have to download from your RPi. Other than that, ASTAP is pretty much automatic once installed.

Do try both solving options as you may find one works better for you depending on your camera and scope FOV combo.

PHD2 or the EKOS internal guiding software?

I started imaging using the capable PHD2 software on ASCOM before I moved to INDI so I know it well and I love it. However you have a choice with EKOS and that choice affects the level of automation you can achieve. I have used the internal guider for a while now and despite some early configuration issues, I am very happy with it, on a really good night, I can guide at around 0.5 to 0.6 RMS on my IOptron CEM60 for perfectly round stars using an OAG. However there are many of our community that love the extra control that PHD2 gives them and some are really expert at using its tweaks that get that extra out of their rigs. So its great we have both but maybe suggest start out using the internal guider first if you are new to PHD2 and also Ekos.

EKOS Internal Guider Pros & Cons

  • laughing Less complex, easy to use, lower learning curve for beginners;
  • smile For some mounts, just works great – if it ain’t broken, don’t try and fix it!
  • smile Works seemlessly with the EKOS Scheduler
  • frown Less tools and logs for when things go wrong, if you have a tricky mount with lots of backlash then PHD2 might be best for you.
  • frown Some mounts require the sophistication and flexibility of PHD to nail good guiding.

PHD2 Pros & Cons

  • smile PHD2’s drift align tool is exceptional especially if you can’t see Polaris and have no other easy options available;
  • smile PHD2 has several support tools on their “Tools” and “View” menus worth having. You might find the guide star calibration graph, Guide Assistant, Drift Align, or Guide Star Stats interesting and important.
  • smile Astroberry has PHD2 log viewer installed!
  • frown Higher learning curve – you may not need the additional features.
  • frown Can be a little overwhelming when first learning astro imaging as a newbie.

For the benefit of those of you who want to try the internal guider, below are my guide settings pictorially – these seem to work well both for my IOptron CEM60 and also my Celestron AVX mount.

ekos internal guider calibration

Guide Configuration – Calibration tab

I always check both (1) “Remove DEC Backlash…” and (2) “Reset guide calibration after mount slews” so after an automated meridan flip, it re-calibrates automatically. All the other options I leave unchecked or as default and it seesm to work well.

ekos internal guider guide

Guide Configuration – Guide tab

The algorithm that seems to work well for me (1) is SEP Multi Star with a SEP Profile (2) of Default.

I always dither (3) when between images – especially good if you are using a CMOS colour camera, as I am (or DSLR)  and want to ensure color mottle is reduced.

ekos internal guiding

Guiding

The picture on the left shows my settings on a good night guiding despite a full moon, I was getting below 0.5 rms on average so much to celebrate there. This was using the Ekos internal guider.

The settings I usually set are:

  1. Auto star is checked to let Ekos select a star automatically.
  2. Exposure length – I start with 1.5 seconds and then try to increase this up to 2.5 seconds depending on the guide performance.
  3. Box size – smallest I can get away with good performance. This will depend on your camera / rig etc.
  4. Always try to bin at 2x if your seeing allows it to reduce download lag.
  5. Look up your optimal mount guiding rate and set it in the mount, then apply it here too!

 People get pretty passionate about guiding so I expect a lively debate here and welcome your comments…

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