Think about lying on your back as a child watching clouds drifting past. This is the nighttime equivalent. The stars etch a trail on the film as they follow their course through the night. The different temperatures of stars show as different colors, the cooler stars glow a warm orange, the hottest stars are a bright blue.
While camping trips make great venues for photographing the sky, sometimes it is difficult to get a full view of it. But here is an opening in the canopy, the lodgepole pines framing the pole star. The camera was aimed at Polaris, and the shutter opened for an hour. The flickering campfires and lamps illuminated the boughs of the trees.
A startrail picture like this is a powerful illustration of the Earth’s motion. The pole star shows almost no motion. The others show longer arcs the further away, but all of them make an equal arc: a one-hour exposure cuts 1/24th of a full circle.
When we consider the impact of computer graphics we usually think of Hollywood motion picture special-effects, or beautifully crafted images and commercials from high-end marketing firms, which both seem like products of the east and west coasts. We don’t think of midwestern artists or public university departments as being part of that world. Yet this is exactly where much of the pioneering work in computer graphics was done and its commercialization was born.
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Cathode ray tubes are a remarkable technology that incorporate many seemingly magic principles of physics. Thermionic emission causes electrons to “boil” off a cathode, high voltage electric fields accelerate and focus them, and magnetic fields steer them to the anode screen where they energize phosphor molecules, which then re-release that energy as visible light!
While developing the electronics to control the CRT and make all this magic happen, we often had to “bring up the spot”, showing the electron beam in one static location, where it could be examined visually and measured with various instruments.
This was always a tricky maneuver, because if the electron beam were allowed to become too intense, the energy transfer to the screen would cause it to heat up to the point where the phosphor would suddenly vaporize, leaving a dark spot that could never be lit up again. Usually, this burn-hole was in the middle of the imaging area, and so the CRT, the single most expensive component in the system, would become instantly unusable.
To avoid this event, there was a standard procedure for bringing up the spot: apply voltage to the CRT and gradually increase it, sneaking up on the level where the spot would become visible, and then avoid going too far. The safe operating zone was rather small.
But even the best procedures cannot anticipate every possible experiment and test that might be needed while inventing new technology. Consequently, there were situations where the beam accidentally and unexpectedly reached the critical phosphor burn level, and whoever was conducting that particular test suddenly realized that they had crossed the threshold and now the CRT had a permanent blemish. They had become a member of “the burn-hole club”.
The burn-hole club comprised everyone who had suffered this unexpected event. It was both an embarrassment, and a badge of honor. It was awful to realize that an expensive component was now worthless, but on the other hand, the tests and experiments that we were conducting were on the cutting edge of our knowledge, the term “cutting edge” implying that injuries were part of the process. Only brave researchers dared to push this edge forward.
I am not a member of this exclusive club, but that is because I had skilled technicians who knew far better than I how to conduct the tests I requested. They were on the front lines of the technology. And as a result, they were the ones first inducted into the burn-hole club.
There is one incident that deserves special mention. It occurred during the development of the brightness calibration method, a critical part of making accurate exposures onto film. We used a photocell at the far edge of the screen. It needed to “see” the spot, and measure how bright it was. The task of figuring out how to do this was assigned to Rick Keeney, who became a master of writing code to control the complexities of driving a cathode ray tube.
To solve this particular problem, Rick came up with a clever algorithm to position the beam directly under the photocell. The exact horizontal and vertical position of the photocell is not known, at least not at first. It needs to be located. So Rick made a first best guess, and then refined it. By moving the beam slightly horizontally and vertically and seeing if the light seen by the photocell increased or decreased while doing so, the beam position could be estimated. Move the beam to where the light measurement was strongest, and that would be the location directly under the photocell.
But if the photocell light level was low, it was hard to know which way to move, so increase the intensity of the electron beam and try again. And if that didn’t help, then it was likely that the beam was not quite where it was expected. So move it over a little bit and try again. This was the strategy for locating the beam and calibrating its brightness. It worked fairly well… until it didn’t.
On one occasion, the beam could not be detected at all. The algorithm increased the intensity trying to measure the light, but as it did so, burned the phosphor in its path. When it failed to detect the beam, it moved over a little bit and burned the phosphor there too. Since the beam was still not detected, it was moved a little more and tried again. The algorithm didn’t have a limit check on position, so it marched all the way across the full width of the screen, leaving behind a tire-track of vaporized phosphor.
This was a spectacular example of damage by electron bombardment, and Rick Keeney, in addition to being an Academy Award winner, also holds the prime honor in the burn-hole club. And I have the privilege of curating the resulting damaged tube.
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Those who know me would be stunned to learn that I have a gun collection. I acquired them in the course of my work trying to make computer images on film in the 1990s. They are electron guns, the mysterious workings at the business end of a cathode ray tube.
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This is the first of three posts describing a now-(nearly)-obsolete technology.
Thomas Edison nearly discovered them. In his experiments with heated filaments in evacuated glass bulbs trying to find a suitable incandescent lamp, there were hints. He noticed depositions of material on the walls of the glass tubes. Many scientific discoveries are preceded not by the expression “Eureka”, but instead by the comment: “Hmm, that’s funny”. If he had followed up on this odd result, he might have also invented the vacuum tube amplifier.
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Today was my last day of employment, and I will now be exchanging the two major foci of my creative time.
My interests in photography and astronomy and art was always secondary to my full-time work as a color scientist, an occupation that has provided a long and fulfilling career.
But this particular outcome was something of a fluke; the education I pursued was a hodge-podge of art, science, and engineering, and my early career was filled with jobs at not-quite-successful entrepreneurial startups that caused my dad to inquire where I was working next, because he wanted to avoid investing there!
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I am at the end of my designated time for this expedition. I must now return from whence I came, to a civilization density that can host a technical conference, and will also develop the latent images captured on my film from this remote beautiful place.
As I reflect on the past few days I realize that there are more things that I would like to do. I never did get to the Goulding Museum, or to the trading post near there (which I was told by the traveler couple was closed on the weekend).
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On this day, I manage to travel to Four Corners, a geographic location that is only meaningful to cartographers marking the human-made political bounds of different territories. There is certainly no physical or geographic rartionale behind it, as the view from the constructed concrete platform holding the National Geologic Survey brass benchmark is the same in all directions.
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It had been a late night with an unexpected adrenaline rush at the end, and so it was predictable that after finally settling down, I would sleep well into the next morning. After showering and shaving, the next order of business was to upload the photos from my digital camera and assess my success at the guided exposures from last night.
Unfortunately, my laptop did not recognize any of the raw (.CR2) image files from the camera’s memory card! This was a setback since I was planning to copy the images to the computer, and then reuse the memory card (I only had two of them and the second was filling rapidly).
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