A camera obscura is a very simple device. Consisting of a dark chamber, with only a pinhole to let light in, it focuses an image on its inside surface. If you want to take a permanent copy, it’s as simple as installing a photosensitive film inside and managing the exposure time. Sounds like a normal camera, right? The difference is the scale — a camera obscura is large enough that humans can stand inside and view the image. Usually, they are large stationary rooms. [Physics Girl] took the show on the road by building a camera obscura out of a rented box truck.
The basic concept is a great one – hire a box truck, and cover the rear opening with cardboard. Cut a small hole in the cardboard, and you’ve created a camera obscura on wheels. The video does a great job of explaining the optical principles behind what’s happening, and there’s even experimentation around how to change the exposure level and focus through modification of the aperture.
The only downside to viewing a camera obscura on video is that you can’t appreciate the resolution and detail visible in real life. Trust us though, it’s better than any HDTV on the market today.
The rolling camera obscura makes for a great experiment which requires little more than some cardboard, tape, and a sunny day. It would be great fun to execute as an educational activity at a school or makerspace. Once you’ve tackled that, perhaps consider the digital version. Video after the break.
You say you didn’t have enough warning to order eclipse glasses, and now they’re too expensive to buy? Or maybe you did order some but they ended up being those retina-combusting knock-offs, and now you’ve got nothing to protect you during the partial phase of Monday’s eclipse? Don’t dump a ton of money on unobtainium glasses — just stick your head in a cardboard box.
You may end up looking like a Box Troll with the aptly named [audreyobscura]’s box on your head, but it really is a safe and effective way of watching the eclipse, or for gazing at our star anytime for that matter. It’s nothing more than a large pinhole camera, with a tiny hole in a scrap of aluminum soda can acting as an aperture. The pinhole in one end of a box casts a perfect image of the sun on a paper screen at the other end of the box. A hole for your head with a proper gasket around your neck — maybe the neck of an old T-shirt would be a bit more comfortable and light tight? — and you’re ready for the show. The bigger the box, the bigger (and dimmer) the image will be, so you’ll want to cruise the local home center for long boxes. Because walking around with a water heater box on your head is totally cool.
[Artlav] wanted to build a digital camera, but CCDs are expensive and don’t respond well to all wavelengths of light. No problem, then, because with a photodiode, a few stepper motors, the obligatory Arduino, and a cardboard box, it’s pretty easy to make one from scratch.
The camera’s design is based on a camera obscura – a big box with a pinhole in one side. This is all a camera really needs as far as optics go, but then there’s the issue of digitizing the faint image projected onto the rear of the camera. That’s fine, just build a cartesian robot inside the box and throw a photodiode in there.
There are a few considerations when choosing a photodiode for a digital camera. Larger photodieodes have higher noise but lower resolution. [Artlav] has been experimenting with a few diodes, but his options are limited by export control restrictions.
Even with the right photodiode, amplifying the tiny amount of current – picoamps in some cases – is hard. The circuit is extremely sensitive to EMI, and it’s inside a box with stepper motors pulled from the scrap bin. It’s amazing this thing works at all.
Still, [Artlav] was able to get some very high resolution images across a huge range of wavelengths. He’s even getting a few images in mid-wave infrared, turning this homebrew digital camera into the slowest thermal imaging camera we’ve ever seen.