Building an Allsky Camera

Thomas is a YuKonstruct member who loves looking up at the night sky. You might remember his previous post on building a telescope from scratch. Recently, the Klondike Visitors Association purchased one of the allsky cameras he developed and had it installed in Dawson City. It is the first camera in the Yukon Astronomical Society’s future Yukon Allsky Camera Network!

Like a lot of people, I love watching and taking photographs of the northern lights. I always have a hard time getting back in the house and going to bed because I feel that I’m missing out on a great show. “What if there is a geomagnetic storm in the next 15 minutes?” Still, I can’t spend every night outside in the cold. On top of that, I have a day job that requires me to have at least one eye open during 8 hours.

In order to keep my sleep pattern happy and reduce my fear of missing out on the activity above my house, I decided to build a camera that would make a short movie of the entire sky and send it to my website in the morning so that I could watch how active the aurora had been during the night.

 

Northern lights are large colorful curtains of light stretching across the sky. It’s quite hard to fit them in the frame of a single photograph. Some people stitch multiple pictures or use wide angle lenses in order to capture the whole show. But individual pictures don’t show the way the aurora borealis flows, unrolls, dims and pulsates. Taking a serie of images and making a timelapse video was the only reasonable way for me to capture the whole information.

In order to build such a camera, I decided to use an astronomy camera (ASI224MC). It has a USB connection and is extremely sensitive to low light. I slapped a fisheye lens (180 degrees) on it to view the entire sky. My first thought was to place the camera outside and run a cable to the house computer through a window. I quickly realized it wouldn’t be very practical and it would anger my roommates to pay a huge electrical bill if I left the window open for the entire winter season. Instead, I decided to bring the computer outside. A Raspberry Pi was perfect for the job. It is small but it’s still a computer with enough power. I created an enclosure from a 4” ABS sewer pipe and ran an extension cord to it. That was it for the prototype. I had just built an “all-sky wireless camera”.

But that wasn’t the end of it. The software part was probably the most time consuming. First, I had to re-learn C++ in order to modify the example code that was provided with the software development kit of the camera manufacturer. Then I had to find a way to stitch all the thousand images from the previous night into a short video. Then I had to automate this video generation, archiving and uploading. After some trials and a few fails, I ended up with a fully automated camera that posted a new video everyday based on the time of sunrise and sunset. The only downtime was caused by construction workers cutting the fibre cable down south or the occasional critter frying itself on an ATCO transformer.

In the end, since I wanted to share that project, I posted an Instructable on how to build your own wireless allsky camera. The popularity of the post lead me to share the whole code on GitHub with an very permissive open source license.

Since then, a lot a people across the world have built their own allsky camera based on my design. Recently, the Klondike Visitors Association in Dawson City purchase the first camera produced by the Yukon Astronomical Society.

Member’s Project: A Telescope Built From Scratch

Why don’t you just buy one?

That’s a question I’ve heard countless times, and when it comes to building a telescope, you really have to think about it twice. After all, buying a decent telescope is quite easy and relatively cheap. You can get a good view at the moon, the planets and some galaxies for a few hundred dollars including shipping to Whitehorse. On the other hand, building a telescope is an arduous task; you have to find the materials, build your own tools and spend hundreds of hours around a polishing stand. it also involves a lot of patience and precision. At first sight, anyone sensible would take 15 minutes to place an order on-line and wait for the telescope to arrive. Well, call me crazy… I chose the DIY option.

glass blank
The starting point: a blank of borosilicate glass

As a maker, I always favor building over buying, even if it costs more money for the final product. You simply can’t buy the pleasure and knowledge that you gain by building something yourself.

mirror
Silicon Carbide seeping through the tiles during rough grinding

Making the mirror of the telescope is the most time consuming part but also the most interesting. First, you need to order a circular piece of glass with a low coefficient of expansion (pyrex, zerodur, borosilicate, etc). Then you need to build a circular tool out of waterproof plaster, cover it with tiles and rub it against the glass with silicon carbide in between. Using finer grit will slowly make the concave surface smoother. Once you’ve reached the desired sagitta, you can polish the surface using a different tool; this one is covered with pitch and the polishing agent is cerium oxide. When you have a nice polished surface, you need to transform that spherical surface into a paraboloid. This is where the time consuming part begins. During that step you will remove a minute amount of glass to approach the perfect theoretical shape. If you complete that step successfully, your mirror will have a surface so regular that if you were to stretch it to the size of a football field, the highest default would only be a thousand of an inch high. Of course, to control the surface with such precision, you need to build a special instrument which takes even more time and material.

mirror on pitch
Polishing the mirror on pitch

When you’ve reach that step, it’s already been a few month since you began the project. However, if you managed to reach the desired precision, you most likely have a better mirror than most commercial mirrors.

Once the mirror is complete, it is sent for aluminizing. During this operation, a thin coat of aluminium is evaporated onto the surface of the mirror; this requires a vacuum pump and a high voltage source. As much as I would like to do it myself, I reckon it is not really worth building an entire vacuum chamber for a single mirror.

mirror_coated
The mirror back from aluminization

The focal length is measured on the finished mirror.  We will use this measurement to design the tube of the telescope. I wanted to use something nicer than plywood so I went for red cedar trims that I resawed to get 1/4″ boards. These boards where assembled together using bird’s mouth joinery to form an hexadecagonal tube (16 sides). Some baffles were laser cut on YuKonstruct’s Epilog laser cutter; these will prevent internal light reflection. The tube was then painted black inside and coated with several coats of spar varnish to make it dew proof.

wooden-telescope
Building the 16 sided tube

The last step consists of putting everything together. A hole is drilled on the side with a hole saw to accommodate the focuser; a cell is built for the primary mirror and a support is made to hold the elliptical mirror in place. I went with a curved vane for the ease of build and for the fact that it will limit diffraction spikes around bright stars.

wooden telescope 25
Curved vane, focuser and mirrors in place

As I was busy building other things, it took about a year to complete the instrument. On the first afternoon after completion, I tried to locate Jupiter in the evening sky; it took about 5 minutes to spot it with the naked eye because the sun was still shining bright above the horizon. Once I found it, I aligned the scope and focused on the planet. As a first observation, I didn’t know what to expect. Well…turns out I saw details on Jupiter that I never saw before on other instruments.

I am now really eager to try it on deep sky objects on a dark winter sky. Next project: make a proper stand for the instrument.

 

first light
First light on Venus and Jupiter

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