Getting the most from Kstars and Ekos
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.
Kstars and Ekos – Dark Frames
Never use Dark frames or a Master Dark captured using other tools, such as APT. Re-take them with your new setup
I discovered this the hard way that you must take new dark frames using Ekos to ensure correct dark frame subtraction in tools like PixInsight to work 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.
Kstars and Ekos – Initial Configuration stuff
- 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:
- 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
Since version 3.5 of KStars, a new plate solving capability has been integrated within Ekos. This is called StellarSolver and it works quite differently to the previous options offered though these are still available under configuration.
StellarSolver is an Astrometric Plate Solver for Mac, Linux, and Windows, built on Astrometry.net and SEP (sextractor) and is meant to be an internal library for use in a program like KStars for internal plate solving on all supported operating systems.
This gives it the following advantages:
- KStars does not require any external applications to perform any of its astrophotography related tasks;
- This solver is completely built-in and supported on all platforms equally – there is no need to install additional software as there was running Kstars on Windows;
- The solver is more efficient so will be faster than before;
- No calls outside of Kstars needed including outside of the internet;
- No Astrometry.cfg file is needed, the settings are internal to the program.
- Directly loads the image data into SEP and then takes the generated xy-list internally from Sextractor into astrometry.net, so there is no need to save any files.
The Index Files are still required for solving images, but the program or the user can specify the folder locations rather than putting them in the config file.
Astrometry / ASTAP / Online Solving
These are still supported but not by default. Should you still wish to use them you need to open Options from the EKOS Align module (once connected of course), and under StellarSolver select an alternative option. Avoid online solving though as this can be very slow and is difficult int he filed wihtout an internet connection.
To install the index files locally, in the Align module Options again select Index Files. Make sure you select a directory other than “All Sources” for the Index File Location first, as this is where they will be stored and you can’t download them until you have done this, click on the required and recommended index files for your telescope configuration to start downloading each one – this a cloudy night job as the downloads can be pretty large!
My personal experience is that the new integrated solver works extremely well, uses less resources and is faster so many congratulations to Robert Lancaster for great work – your can see his project on GiHub here.
Dithering is not procrastinating!
I highly recommend turning on Dithering in the Guide module Options…
To dither means to shift the pointing of the telescope slightly in random directions between exposures, usually by a couple of pixels – so why is this important? When you stack a collection of images that have been dithered, your stacking software will recognise pixels that are not present in different frames – this means that hot and cold pixels, cosmic ray artifacts, and fixed pattern noise, and even satellite or airplane trails can be removed during the stacking process giving you better signal to noise ratio. The Sigma rejection stacking method, available in most astronomical image-processing programs, applies a mathematical algorithm to examine every pixel and discard outliers that are very different from the average in your group of images. This means that if you have 10 frames and a hot pixel is only showing up in one particular location on a given frame, the algorithm replaces it with an average from the other frames. For the Sigma algorithm to work, you need a minimum of 10 frames.
Setting Dithering up in Ekos is really simple – it’s a tick box and usually the defaults work fine – what’s not to like about dithering!
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
- Less complex, easy to use, lower learning curve for beginners;
- For some mounts, just works great – if it ain’t broken, don’t try and fix it!
- Works seemlessly with the EKOS Scheduler
- 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.
- Some mounts require the sophistication and flexibility of PHD to nail good guiding.
PHD2 Pros & Cons
- PHD2’s drift align tool is exceptional especially if you can’t see Polaris and have no other easy options available;
- 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.
- Astroberry has PHD2 log viewer installed!
- Higher learning curve – you may not need the additional features.
- 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.
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.
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.
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:
- Auto star is checked to let Ekos select a star automatically.
- Exposure length – I start with 1.5 seconds and then try to increase this up to 2.5 seconds depending on the guide performance.
- Box size – smallest I can get away with good performance. This will depend on your camera / rig etc.
- Always try to bin at 2x if your seeing allows it to reduce download lag.
- 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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