My Grandmother King gave me my first camera for my eighth birthday - a Kodak Brownie. My parents had a camera, but I wasn't allowed to use it. This was my camera. I also received two rolls of black and white film and a voucher for developin. Of course I did what most eight year olds would do - I took pictures of the sky, the side of the house, my sister, the dog - twelve exposures in all. A week later the prints came back and you can guess how bad they were. The second roll was a bit more better, but I never developed the artistic skill. But I did I did become fascinated with devices that capture images and have designed and built a few over the years.
Some of you are excellent photographers. My friend Om happens to be just such an artist and I believe he is writing a book on the subject. My sister Corinne is an artist who uses photography and computers to offer quirky commentary. I'll be content with my simple snapshots and videos enjoying the art of others. And I'll think about the process and tools.
The term camera conjures up something that focuses light on film or an electronic image sensor where an image is captured. Still or moving images, but almost always visible light. Currently the definition is being extended to computational photography - the processing that goes on in your iPhone for example. I stretch the definition a bit.
For me a camera is something that captures some event or series of events in time. It doesn't have to be visible light, but any form of electromagnetic radiation and or something a bit more exotic - like charged particles or the shaking of space-time.
I first came to this way of thinking on Sulphur Mountain near Banff, Alberta. I was almost thirteen and had gone over to a curious little shack on one of the mountains twin peaks while my parents had lunch at an observation deck a half kilometer away. The two young men in the shack turned out to be cosmic ray physicists. They patiently explained in kid language how they captured muons. What they were really doing is capturing and recording part of a particle shower that came from cosmic rays striking the atmosphere twenty or so kilometers up. They'd run these recorded events through some calculations and would be able to say something about the shower and from that perhaps something about the Universe. After listening I said something like "you've built a cosmic ray camera. That tape is your film and you turn it into something like a picture" They nodded , smiled and showed me how an image could be abstract and still give a lot of information. That day would change my life.
Since then I've been around my share of particle physics detectors - essentially cameras that capture the aftermath of violent particle collisions at places like CERN. I've also used optical and radio telescopes that, typically after a lot of computation, produce real or abstract images of places and events back in time. It still astounds me to look at parts of the Universe as it was twelve or thirteen billion years ago. And for fun I even designed a homemade digital camera back in the 80s.
Cameras capture images that can be meaningful. Images that can be artistic, historical or even offer evidence of Nature's workings. Some of the techniques are familiar and straightforwards, others are sometimes deeply computational. And if you consider the eye-brain combination a camera, as many do, there are surprises We usually think of an image falling on an imaging surface and being turned into a more of less faithful representation of the image. In fact there is a lot of processing that goes on between the front of the retina and the brain. What eventually turns into an image has very little in common with what fell on the retina. Our brain stitches together information, often out of order and spread over several seconds, to construct an approximation of reality we think of as the real thing and a sense of "now" that is equally artificial. The comic strip is a nice example of something that is temporally impossible that happens in your brain all the time. It turns out temporally out of order processing often happens in computational photography. And then there are many instruments you might not think of as a camera that are much closer to the classical definition.. things like MRI, ultrasound imaging, radio telescopes and the like.
Back to this $16 million Canadian camera...
CHIME is a radio telescope at the Dominion Radio Astrophysical Observatory near Caleden, British Columbia. It consists of four 100 meter by 20 meter upward facing semi-cylinders that are sort of like snowboarding half-pipes. Sprinkled up and down the foci the semi-cylinders are 1024 radio receivers that operate between 400 and 800 MHz .. covering a frequency range similar to that of UHF television - a frequency range was chosen to detect a signal hydrogen emits.1 That's where the name comes from - the Canadian Hydrogen Intensity Mapping Experiment.
An enormous amount of computation takes place in several steps after the radios receive the signal. The first step sets the instrument apart. You may have a wifi router that does beam forming. Basically you use a small array of antennas and the properties of radio waves to construct a "beam" to the source.2 CHIME creates 1024 beams listening to over 16,000 frequencies (think of them as colors) all imaged 1000 times a second. While beam-forming adds to the computational load it dramatically decreases construction costs over a mechanically aimed antenna and for this application is a very clever strategy. The computing just behind this is equally clever. Sixteen million dollars to get this kind of data over what will be several decades of life is a bargain. The electronic and computer designs are elegant and if you're into that sort of thing you should look into the details.
The hope was it could detect an unusual recently discovered event called a fast radio burster. At first some suggested the short radio bursts of a thousandth of a second or so might be signals from extraterrestrials as no one had a compelling physical explanation. They're very rare and transient. Before CHIME only one burster called FRB121102 has been seen to repeat sending out about 100 irregularly spaced bursts since its discover in 2012. A few hypothesis have been made, but studying a single event can lead you astray. Then CHIME switched on for three weeks last Summer and thirteen new events were detected even though it wasn't fully functional completely. This is far and away the most sensitive camera in the world for studying these events. It is also well suited for mapping - making images of - hydrogen clouds in a much younger Universe, studying a special class of neutron stars called magnetars, and answering a number of other astrophysical and cosmological questions. There's the added bonus of looking at the sky with a new type of camera. You tend to discover things you hadn't imagined.
Human beings have become remarkably adroit at extending and even going beyond their senses as we try to understand the world. CHIME is easily one of the most beautiful cameras ever made.
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1 The 21 centimeter line of hydrogen is a great signal for studying the distribution of hydrogen atoms in the Universe. It would be far too short to be detected by the telescope, but distant hydrogen is red shifted down to this frequency range.. Since the emission line is very narrow and well known, you can calculate the redshirt and therefore the distance of the gas.
2 Beam forming is done by changing the signals phase at each antenna in an array in such a way that constructive and destructive interference create a pointed beam. It works well for wavelengths not much different from the antenna size. Wifi base stations aren't very accurate, but they don't have to be. You can also do it with sound leading to some interesting pranks.
We Canadians are very clever;)
I love the cartoon!
Posted by: Jheri | 03/04/2019 at 06:16 PM