This is the first of a series of articles. As I'm always experimenting and tuning my setup, I'm not sure how many more articles I'll be writing.
A few years ago I began to introduce myself to astrophotography. I had some fairly nice equipment back then: a SkyWatcher HEQ5 mount, a Meade ACF 8", guide scope and camera, a borrowed reflex, laptop, 12v car battery.
Although this is pretty much entry level equipment, barely sufficient to getting started, it had been already quite expensive (almost 2000€ just for scope and mount, even though the scope was second hand), bulky and heavy. I ended up barely using it, both because of a relatively steep learning curve and because I honestly was getting tired of carrying around 20/30KG of equipment with barely any tangible result.
Then a few things happened: the mount was stolen, I sold the optical tube, and ended up moving to London, where I embraced a new "astronomical philosophy": the lighter, the better.
I was also lucky that this was when some fancy new products like the Star Adventurer started to go "viral", which contributed to lower prices, good support, and good publicity as well, so it wasn't long until I got mine too.
Of course, the Star Adventurer is only half of the story: you also need optics, and some kind of camera. The Star Adventurer is often seen as the best pal to DSLR cameras, it can even trigger shooting using a specific cable, but what about other cameras, like CMOS/CCD astronomy cameras? I wanted to use a Mono camera with filter wheels, specifically an ASI 1600MM. This means you need to use a laptop to drive the camera, download the images (no SD Card slot there), rotate the filter wheel, etc. This might not seem a complicated addition, afterall everyone has a laptop, nowadays. The problem is that a laptop's battery, out in the cold nights, doesn't usually last long. You'd need to bring some sort of power source, like a 12V car battery (heavy, bulky equipment again). You might also want some table and chairs, as it's probably not a great idea to just leave a laptop on the wet grass while shooting.
Long story short, this is when a second "viral" world comes in handy: Single Board Computers, with its most famous example, the Raspberry Pi.
I'm now trying various alternative boards, but by far right now the Raspberry Pi (specifically the 3rd version) is the most reliable, the one I'm still actively using.
This is my typical setup/workflow:
The ASI camera and filter wheel are connected directly to the Raspberry Pi. The Raspberry is usually strapped nearby, either to the mount, on the counterweight, or on the scope tube. Being very lightweight, it doesn't really affect balancing, and it doesn't affect the mount load.
The Raspberry Pi is powered by a 20Ah power bank, the same you normally use to charge your mobile phone (I use the 20Ah version to get more "juice", since the Raspberry Pi, despite being a very low power device compared to a laptop, is still relatively power hungry).
For the software part, the Raspberry Pi runs an INDI server, and your client of choice to manage the imaging part. You can use KStars/Ekos, which is usually the best choice among INDI clients, and it's a very nice software indeed, but instead I'm developing my own scripts (which soon will become a webapp). You can have a look at my repo here: https://github.com/GuLinux/indi-lite-tools, but I'll be making a specific post later on. An easier, but less performant and more power consuming alternative, is to use a desktop version of Raspbian (or Ubuntu), and simply use VNC to remotely control your raspberry Pi.
Finally, you'll still need a laptop: pointing your target, adjusting the field of view, focusing, and exposure, they all need you to view what your camera is currently pointing. But here comes a little trick: you need a laptop only for these initial steps, which with pratice can last only 15/30 minutes. You won't need any large battery for your laptop, simply because you won't be using it for more than half an hour. And to get the images, you don't need to connect your laptop to the camera (and filter wheel), nor you need an ethernet cable from the Raspberry Pi to the to the laptop: the Raspberry Pi v3 has a builtin wifi interface, that can also act as an Access Point.
You can then simply connect your laptop to your Raspberry Pi Wifi, use KStars/Ekos to connect to the INDI server running on the Raspberry, and wirelessly get the images. Then, you will start the sequence on the Raspberry Pi itself, turn off your laptop, and... just enjoy the night sky :)
Or if it's particularly cold, and/or you're tired and want to rest, you can go inside (your house, your car, tent, or whatever), and wirelessly check on your sequence.
In summary, these are the advantages of this setup:
- Low power requirement (a large capacity mobile phone powerbank is more than enough to run it for multiple nights).
- Extremely lightweight, it's even possible to bring your astro equipment with you on a plane, effortlessly. Even the 20Ah power bank weights less than half a Kilogram.
- Hardware compatibility (INDI can support lots of devices).
- "Plugin friendly": a Raspberry Pi can be expanded with more hardware, both using the USB ports or GPIO. I tried connecting an RTC clock, an OLED display (showing current sequence progress), a buzzer to warn me if an error occured, a GPS module to get the exact coordinates, etc.
And the disadvantages:
- Setup can be very difficult for people not used to Linux command line (althought the VNC method described above is fairly easy). I'm working on a "provisioning script" that can easly setup the Raspberry Pi in just a couple of simple steps.
- Low transfer speed: the Raspberry Pi 3 still uses USB 2.0. With my setup, I usually have short exposures (under 60 seconds, sometimes even just 15 seconds), and the Raspberry takes up to 4 seconds to save an image, before shooting the next one. This means that a significant portion of the shooting time will be wasted waiting for image saving. Low USB speed also significantly increases Amp Glow. This is why I'm currently experimenting with some USB3 boards, instead of the raspberry.