Astro Session Workflow - Part 2

Part 2 - Software

Before we get too far into this section, I’ll point out that I use a Linux laptop with Kubuntu installed to drive my rig. If you’re a Windows user, there are many options out there for you - chief being NINA, Sequence Generator Pro and Astro Photography Tool. I have no knowledge of these programs, so you are going to be on your own if you use them.

If you are running Linux, but not an Ubuntu-based distribution, then the PPA package repository listed on the INDI website won’t work for you. You’ll need to build KStars, Ekos and INDI from source code. This is not as difficult as it sounds, as there are scripts available that will do all the hard work for you, but is time consuming. You also need to be comfortable with working at the command-line as there are no GUI tools to do it for you.

I have successfully compiled the software suite from source on a non-Ubuntu system, but it was using a Debian-based package manager with the .deb packages.

If the previous two paragraphs mean nothing to you, then going with an Ubuntu-based Linux setup is your best option.

KStars / Ekos / INDI

The software I use is called KStars and is part of the KDE environment. Within KStars is a module called ‘Ekos’, which handles all the work of guiding, focusing (if you have an electronic focuser installed) and image capture. Underlying Ekos is ‘INDI’, the hardware abstraction layer that provides an API interface between the physical devices and Ekos. (Windows-based software operates in a similar way, and the equivalent of INDI is called ASCOM.)

By itself KStars is a reasonably featured planetarium package that will allow you to explore the night sky. I have troubles with moving the view around and usually end up ‘upside down’, so tend not to use KStars as a planetarium package all that much.

KStars/Ekos/INDI is available on the Apple/macOS platform as well, and works in an identical manner to the Linux version.

It’s just been announced on the INDI forum that it’s possible to run KStars on a Windows device through WSL (Windows Services for Linux) and a little bit of command-line work. The article (with screenshots) can be found here: https://www.indilib.org/forum/general/14409-instructions-to-run-kstars-ekos-indi-under-windows-wsl.html. If you want to try KStars and don’t want to try Linux or macOS then this is your best option.

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Update - 2024-09-01

The INDI website and forum has been upgraded since I originally wrote this article. The link above will show you the text of the instructions but all the images and screenshots are missing.

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If you have the correct hardware, then INDI is able to control a fully automated observatory. This includes opening the roof, carrying out the imaging sequence and then closing the observatory when completed. If you have a weather monitor or all-sky camera installed then INDI can also abort the imaging sequence and close the observatory if clouds or bad weather appear.

INDI is a true client-server configuration. It’s possible to run INDI as a server on a remote computer that has all the imaging hardware connected to it and control it from another computer (the client). There are many instances of people using a small computer (such as a Raspberry Pi) as the INDI server in their observatory or back yard and controlling it from the warmth of their house. I run a stand-alone setup where the INDI server and client software are running on the same computer. This means that I need to take precautions to protect my laptop from environmental issues such as dew and condensation. (See my Gippsland Star Party report for an extreme example.)

When you run KStars for the first time, it will ask a few questions to help get you up and running. The most important question to answer correctly is your geographical location - this allows KStars to show you the correct night sky and take into account daylight saving and the like.

Ekos Profiles

Key to Ekos is the concept of a hardware profile. These are different sets of imaging hardware configurations, allowing you to use different equipment without having to reconfigure everything.

A profile will specify the mount and camera(s) you are using, along with more esoteric hardware such as electronic focusers, filter holders and more.

Along side your profile, there is what’s called an ‘optical train’. This ties your hardware together into one unit. (Yes, this does seem like a duplication of the hardware profile. I’m uncertain as to why the Ekos developers took this design decision.)

It’s from the ‘Optical Trains’ window that you define your actual telescope, via the ‘Telescopes & Lenses’ button at the bottom-left. This window allows you to enter all the details of your telescopes (and camera lenses if you’re using a DSLR for imaging).

All of this configuration work should be done before you take your equipment outside to begin imaging!

I strongly suggest that you assemble all your equipment inside and test it thoroughly. This ensures that you won’t be struggling in the dark to resolve why something isn’t working. Trust me - there’s nothing more frustrating than trying to reassemble your entire rig in the dark when you’re chasing down a problem.

Polar Alignment

When taking long exposure image, an accurate polar alignment is very important. If you aren’t using the guiding module with a dedicated guiding scope and camera, then a poor polar alignment will see the stars creating lines as they move across the sky in a different direction to your mount. At longer focal lengths polar alignment becomes even more critical. (An extreme example of star trails are those images of circular star paths around the Celestial Pole.)

If you’re guiding then an accurate polar alignment will mean less work for your guide software and less work for your mount. Which results in better images for you.

There are multiple ways of properly aligning your mount with your respective Celestial Pole. You can be ‘old school’ and use the polar scope in your mount. Your mount will probably have an alignment routine built into it’s controller. In conjunction with a 3-star alignment routine, you can tune the polar alignment to a reasonable accuracy. You can use the alignment routines in your astrophotography software (Ekos has this feature, and I know that NINA has at least 2 separate plugins you can install). You can also use a very accurate (but very slow) method called ‘Drift Alignment’ which (as I understand it) relies on taking long exposure images and aligning your mount so that the stars trail in particular directions within the image frame. I’ve never used this method, so can’t comment further.

I have a Polemaster camera, from QHY. You can download the software from their website for your respective platform (Linux, macOS and Windows). Note that your Linux setup must be able to install packages using the .deb file format. (Which means RedHat users will need to do more work to install the software.)

Polemaster - Polar alignment Software

The Polemaster software is accurate to about 30 arc-seconds - more than good enough to allow you to take unguided images of a reasonable exposure, and definitely good enough to ensure accurate guiding.

when you connect the Polemaster camera to your imaging device and start the Polemaster software you will see a screen similar to Image 1 below.

Continuing the setup routine, we select our respective hemisphere (Northern or Southern) and the image setting (exposure and gain) so that we can see the stars within the camera’s field of view.

In the Southern Hemisphere, we don’t have a suitable pole star (that’s Polaris, for you Northern Hemisphere readers) and we have to use the Octans set of 4 stars as our guide.

After selecting Sigma Octans and aligning the star template with the associated stars, we rotate the mount twice and the Polemaster software will take a series of 3 images. By some clever mathematics, the software is able to deduce the difference between your mount’s axis of rotation and the location of the Celestial Pole.

After using the mount’s adjustments (altitude and azimuth) to align the mount’s axis of rotation with the Celestial Pole, we then move onto the last step - the fine adjustment.

By using the mount’s adjustments, we move the mount until the red cross is within the green square. (I took these images on my desk, with the camera’s lens cap firmly in place. After going through the above steps, the cross and box should be almost on top of each other.)

Having said all that, there have been times when I am imaging from a new location and have only a rough idea of where the Celestial Pole is. In these cases, I will use the Ekos Polar Alignment routine to get a reasonable alignment (to within a couple of degrees) and then switch to the Polemaster. Use of Ekos’ Polar Alignment routines are a bit outside this document, so I’m not going to cover it.

Ekos Pre-imaging Sequence

Now that our mount is polar aligned, we can get on to the next steps in the sequence. Even now, I still manage to forget one of these on occasion and spend ages wondering why nothing is working… Having a checklist will certainly help!

Focus

If you’re using a manual focus system, either by looking at the view screen on your DSLR to watch the stars change size as you gently move the focus adjuster, or via a Batinov mask, you can safely skip this step. With my dedicated astro-camera and electronic focuser, I no longer have a live-view option.

The Ekos auto-focus module has more options and settings than I can count. Some methods work better for reflector (mirror) telescopes such as Newtonians, SCTs and Maksutovs, whilst others may work better for refractor telescopes. I strongly suggest you invest time in researching what methods work best for you. There are some excellent video tutorials on YouTube (https://www.youtube.com/@johneevans1), as well as helpful posts on the INDI forums (http://www.indilib.org/forum.html) and you cannot go past the KStars documentation.

Align

Alignment is merely ensuring that your chosen target is in the exact centre of your image. Ekos will take an image, calculate the exact location of where your telescope is pointing (a process called ‘platesolving’) and move the mount so that it’s pointing closer to where it’s supposed to be.

The default target accuracy is 30 arc-seconds, and my mount can usually get there within 3 iterations.

Guide

Now that the mount is aligned to the target, and the telescope is properly focused, we can turn our attention to guiding.

Guiding is the simple process of ensuring that your telescope does not stray off the target as the night progresses.

In my case, I have a separate telescope and camera dedicated to guiding. There are also pieces of equipment called an ‘Off-Axis Guider’. They are merely a small mirror that intrudes into the telescope’s light path and reflects that light into a dedicated guiding camera. As the main camera sensor is usually square or rectangular, and the light path is circular, there is some ‘unused’ space that the mirror protrudes into. Doing it this way makes sure that there’s no blockage of light reaching the main camera sensor.

Before we can begin guiding, Ekos needs to calibrate the mount in both axes (Right Ascension and Declination) so that it knows how much to move the mount. Calibration involves taking a series of images with the guide camera and moving the mount a fixed amount relative to the stars seen by the guiding camera. Once the software has calculated all this, it will start guiding.

Guiding accuracy is measured in arc-seconds and the lower the total error, the better your guiding will be. A lot of astrophotographers spend a huge amount of time stressing over their guiding accuracy. Once you are guiding at levels smaller than your camera’s pixel size, there’s really no need to worry, as the guiding error can’t be seen in the images.

I use the Ekos guiding module because it works and I don’t need to learn another piece of software. Having said that, there is an alternative called ‘PHD2’ (Which stands for ‘Push Here, Dummy v2’) which many astrophotographers use. Yes, PHD2 integrates tightly with Ekos and it provides an alternative if you need it.

One handy hint - don’t try guiding near the Celestial Pole. The very small movement of the stars will confuse the guiding software and it will more than likely fail. You also need a good number of stars visible to the guide camera. I’ve had several targets where there weren’t many visible stars and I could not get guiding to work well.

Test Frames

The next step is to take some test images to see what exposure settings are going to work best for the night’s imaging. To keep things simple, I use the same gain (analogous to the ISO setting on a DSLR), offset (a small amount of signal added to each pixel to prevent them clipping to pure black) and camera temperature for each session.

The only setting I change is the exposure time. Depending on my location, the target, and the filter I am using, they can be as short as 10 seconds or as long as 3 minutes.

When I’m imaging at home with the UV/IR filter, I will often use 20 second exposures as this gives me a good compromise between good data and not capturing too much light pollution. For the L-Enhance filter, I tend to go for 120 second exposures. Longer exposures require more accurate guiding.

I will review my test frames with an image viewer and see which one gives good data without being overexposed.

Run Sequence

Finally, we get to the point where I can start capturing data of my selected target. The sequence is merely telling Ekos to capture ‘X’ image frames.

The status window shown above will display the focus curve (top-right) the current guiding error plot (lower-right) and the most recent image. There are also two progress indicators that show the number of images taken, and the overall progress (if you’ve set up multiple sequences to run consecutively).

When everything is finished, I’ll park the mount back in it’s home position, turn off the cooler in the camera and retract the auto-focuser to it’s zero location. Once these steps have all completed, I will turn everything off and start packing up.

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• Astro