Astrophotography is an expensive hobby. When assembling even a basic setup consisting of a telescope, camera, guiding equipment and mount, you can easily end up with several thousand dollars worth of gear. To reduce the monetary sting a little, [td0g] has come up with an innovative homebrew mount and guiding solution that could be assembled by almost any dedicated amateur, with the parts cost estimated around $100. The accuracy required to obtain high-quality astrophotographs is quite demanding, so we’re impressed with what he’s been able to achieve on a limited budget.
The inspiration for this design comes from an incredibly simple star tracking device known as a barn-door tracker, or Haig mount. Invented by George Haig in the 1970’s, this mount is essentially nothing more than a hinge aligned with the Earth’s axis of rotation. A threaded rod or screw, turned at a constant rate, is used to slowly open the hinge so that a mounted camera tracks the apparent motion of the heavens. As a result, long exposures can show pinpoint images of stars and sharp details of deep-sky objects, instead of curved star trails. [td0g] adapted this technique to drive a more traditional telescope mount, using barn-door-like drive screws on both the right ascension and declination axes. A pair of NEMA 17 stepper motors drive 4-mm pitch Acme threaded rods through toothed pulleys 3D printed from PETG.
Speaking of 3D-printed parts, this build is a good example of judicious use of the technology: where metal parts are warranted, metal parts are used, and printed plastic is relegated to those places where it can adequately do the job. [td0g] has placed the STL files for the printed parts on Thingiverse in case you want to replicate the drive.
The non-linear relationship between the threaded rod rotation and right ascension drive rate usually limits the length of exposure you can reasonably achieve with a barn-door tracker. To adjust for this, [td0g] created a lookup table in firmware to compensate the drive and allow longer exposures. He mentions that the drive will operate for three hours before it hits the end of the screw’s travel and needs to be reset, but if he can manage three hour exposures, his skies must be much darker than ours!
As the cost of high-resolution images sensors gets lower, and the availability of small and cheap single board computers skyrockets, we are starting to see more astrophotography projects than ever before. When you can put a $5 Raspberry Pi Zero and a decent webcam outside in a box to take autonomous pictures of the sky all night, why not give it a shot? But in doing so, many hackers are recognizing a fact well-known to traditional telescope jockeys: seeing a few stars is easy, seeing a lot of stars is another story entirely.
The problem is that stars are fairly dim; a problem compounded by the light pollution you get unless you’re out in a rural area. You can’t just brighten up the images either, as that only increases the noise in the image. A programmer always in search of a challenge, [Benedikt Bitterli] decided to take a shot at using software to improve astrophotography images. He documented the entire process, failures and all, on his blog for anyone else who might be curious about what it really takes to create the incredible images of the night sky we see in textbooks.
In principle it’s simple: just take a lot of pictures of the sky, stack them on top of each other, and identify which points of light are stars and which ones are noise artifacts. But of course the execution is considerably more difficult. For one thing, unless the camera was on a mount that was automatically tracking the sky, the stars will have slightly moved in each image. To help with this process, [Benedikt] used a navigational trick that humanity has relied on for millennia: mapping constellations. By comparing groupings of stars in each image, his software is able to accurately overlay each image.
But that’s only one part of the equation. In his post, [Benedikt] goes over the incredible amount of math that goes into identifying individual stars in the sea of noise you get when a digital image sensor looks into the black. You certainly don’t need to understand all the math to appreciate the final results, but it’s a fascinating read for those with an interest in computer vision concepts.
Astrophotography is one of those things you naturally assume must be pretty difficult; surely something so awesome requires years of practice and specialized equipment which costs as much as your car. You shake your fist at the sky (since you have given up on taking pictures of it), and move on with your life. Another experience you’ll miss out on.
But in reality, dramatic results don’t necessarily require sticker shock. We’ve covered cheap DIY star trackers before on Hackaday, but this design posted on Thingiverse by [Tinfoil_Haberdashery] is perhaps the easiest we’ve ever seen. It keeps things simple by using a cheap 24 hour clock movement to rotate a GoPro as the Earth spins. The result is a time-lapse where the stars appear to be stationary while the horizon rotates.
Using a 24 hour clock movement is an absolutely brilliant way to synchronize the camera with the Earth’s rotation without the hoops one usually has to jump through. Sure you could do with a microcontroller, a stepper motor, and some math. But a clock is a device that’s essentially been designed from the ground up for keeping track of the planet’s rotation, so why not use it?
If there’s a downside to the clock movement, it’s the fact that it doesn’t have much torque. It was intended to move an hour hand, not your camera, so it doesn’t take much to stall out. The GoPro (and other “action” cameras) should be light enough that it’s not a big deal; but don’t expect to mount your DSLR up to one. Even in the video after the break, it looks like the clock may skip a few steps on the way down as the weight of the camera starts pushing on the gears.
It seems like [Jason Bowling] never gets tired of finding new ways to combine the Raspberry Pi with his love of the cosmos. This time he’s come up with a very straightforward way of focusing his Celestron 127SLT with everyone’s favorite Linux SBC. He found the focus mechanism on the scope to be a bit fiddly, and operating it by hand was becoming a chore. With the Pi Zero and a stepper motor, he’s now able to focus the telescope with more accuracy and repeatability than clumsy human fingers will be able to replicate.
On this particular type of telescope, the focus knob is a small knob on the back of the scope (rather than on the eyepiece), which just so happens to be the perfect size to slide a 15mm bore pulley over. With a pulley on the focus knob, he just needed to mount a stepper motor with matching toothed pulley next to it and find a small enough belt to link them together. Through the magic of Amazon and McMaster-Carr he was able to find all the parts without having to make anything himself, beyond the bent piece of aluminum he’s using as a stepper mount.
To control the stepper, [Jason] is using an EasyDriver connected up to the Pi’s GPIO, which along with a 5V regulator (which appears to be a UBEC from the RC world) is held in a tidy weather proof box mounted to the telescope’s tripod. The regulator is necessary because the whole setup is powered by a 12V portable “jump start” battery pack for portability. Handy when you’re stargazing in the middle of a field somewhere.
[Jason] promises a future blog post where he details how he used Flask to create a web-based control for the hardware, which we’ll be keeping an eye out for. In the meantime, he reports that his automated focus system is working perfectly and keeps the image stable in the eyepiece even while moving (something he was never able to do by hand).
One of our favorite turnips, oops, citizen scientists [The Thought Emporium], has released his second Grab Bag video which can also be seen after the break. [The Thought Emporium] dips into a lot of different disciplines as most of us are prone to do. Maybe one of his passions will get your creative juices flowing and inspire your next project. Or maybe it will convince some clever folks to take better notes so they can share with the rest of the world.
Have you ever read a recipe and thought, “What if I did the complete opposite?” In chemistry lab books that’s frowned upon but it worked for the Reverse Crystal Garden. Casein proteins make cheese, glue, paint, and more so [The Thought Emporium] gave us a great resource for making our own and demonstrated a flexible conductive gel made from that resource. Since high school, [The Thought Emporium] has learned considerably more about acoustics and style as evidence by his updated cello. Maybe pulling old projects out of the closet and giving them the benefit of experience could revitalize some of our forgotten endeavors.
When somebody tackles an engineering problem, there are two possible paths: they can throw together a quick and dirty fix that fits their needs (the classic “hack”, as it were), or they can go the extra mile to develop a well documented solution that helps the community as a whole. We cover it all here at Hackaday, but we’ve certainly got a soft spot for the latter approach, even if some may feel it falls into the dreaded territory of “Not A Hack”.
Even if you aren’t terribly interested in peering into the infinite void above, the extremely detailed write-up [Gary] has done contains tons of multidisciplinary information that you may find useful. From showing how to modify the Pi’s boot configuration to enable true hardware UART (by default, the Pi 3 ties it up with Bluetooth) and level shifting it with a ST3232 to a breakdown of the mistakes he made in his PCB layout, there’s plenty to learn.
Skywatching is a fascinating hobby, but does have the rather large drawback of needing to be outside staring at the sky for extended periods of time. Then there’s the weather to contend with, even if you’ve got yourself a nice blanket and it isn’t miserably cold, there might be nothing to see if cloud cover or light pollution is blocking your view.
The software side is fairly straightforward: 10 second exposures are taken all night long, which can then be stitched together with ffmpeg into a timelapse video. [Jason] was concerned that the constant writing of images to the Pi’s SD card would cause a premature failure, so he set it up to write to a server in the house over SSHFS. Adding a USB flash drive would have accomplished the same thing, but as he wanted to do the image processing on a more powerful machine anyway this saved the trouble of having to retrieve the storage device every morning.