The Burn-Hole Club

The coils that provide the magnetic force to move the electron beam

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.

The trail of damaged phosphor, leading right off the edge of the screen.
Rick with a more public acknowledgement of his skills in pushing the cutting edge of science and technology.

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Cathode Rays

The 100th anniversary of the cathode ray tube.

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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Retirement Inauguration

The logo for a project called Mongoose, an early system that was able to compute and send images to color copiers and printers.

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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Monuments at Night, Nov 6

Mitten at midday

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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Monuments at Night, Nov 5

The Orion Nebula, the central star in Orion’s sword.

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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Monuments at Night, Nov 4

Moon over Monument

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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Monuments at Night, Nov 3

An accumulation of light.
Nov 3, 2005, Monument Valley AZ
Pentax 6×7, E200 push 1-stop, 90 minutes at f/4

I am staying at the Hampton Inn in Kayenta Arizona.  It is not your usual traveler’s stopping place that I have become accustomed to in my business travels.  It is an attractive contemporary adobe building, tastefully appointed with beautiful Navajo art and artifacts.  Gentle native music is piped to the public areas.  An interesting Navaho outdoor exhibit is also well presented.  The native American flavor is augmented by modern conveniences—full breakfast, wireless internet, pool, patio, and an attractive and comfortable lobby.

Since the cloudy skies had kept me in, I suffered another full night of sleep.  Now, unexpectedly alert at an early hour, I noticed all of these niceties at breakfast while I started planning my day.

I also noticed an older couple, or rather, they noticed me.  And for some reason, maybe because I was alone at a table making entries in my notebook, they decided that I needed company.

They were gregarious and garrulous, she a travel writer of twenty years for the Chicago Tribune, still writing columns for various papers, and he an attorney, no longer practicing, both of them skilled with words and language, both widely travelled.  They were adorned with native attire: turquoise necklaces, silver wristbands, belt adornments.  She wore a flowered dress, hat, and moccasins.

They told me of coming here every year for fifty to replenish their souls, wandering down backroads to old trading posts and remote locations.

In recent years however, they had been warned to avoid certain roads.  Drug dealers are unforgiving and have killed police and bystanders alike for reasons that make sense only to them.  He (Jim, the lawyer), had once carried firearms for protection, but now doesn’t—not because they’re illegal, but because they’re impotent against the firepower of drug dealers.

This gave me pause as I considered my typical nighttime activities.  I should probably avoid remote roads to avoid inadvertently crossing paths with some late night transaction.  But that would be restrictive, the best dark sky sites are found on such roads.

I listened to more.  They had stories to tell, fascinating facts, history and lore, and each triggered a further story from the other, taking turns to tell them to me.  I was quite impressed, and decided to try and follow some of their directions to the local destinations they described.

Among them was the Shonto trading post.  The road to it was covered with rippled sand, an advance of the desert onto our human trails.  The last section of road down to the valley was a rough rock ledge, blasted from the cliff with spent guard posts—cabled together but eroded and yanked out of their moorings.

The sand-covered road to Shonto.
The last part of the steep descent to Shonto Trading Post.

The trading post itself was mostly empty shelves, but provided bread and milk to local customers.  When there is nothing else, this is the center of mercantile life and the focus for goods that cannot otherwise be hunted or farmed.

And it was apparent that I stood out from the local customers.  One of them, standing outside the trading post sized me up and had to find out “Where are you from, Alaska?”  I knew that I would never pass for a local, my complexion and attire was not frequently seen here, but I must really stand out, even from the other tourists! 

I returned from my excursion and on the way back encountered the structure that supplied coal cars from the nearby Peobody mine via tall storage elevators.  It had been lit up like a giant diamond ramp the night I drove in.  The elevators were fed by a conveyor belt from the mine and in turn fed rail cars on a train powered by overhead 500 kilovolt electricity!  [Update 2019: the facility is closing due to the diminishing use of coal in the U.S.]

I have plans for tonight.  I will test my “twilight exposure model” by taking pictures with my digital camera and comparing with the sun elevation data that I downloaded from the US Naval Observatory.  In preparation, I cleaned the image sensor.  I did not have the proper tools to do this.  When the nearest camera store is hundreds of miles away, one must improvise, so with the turkey baster I had acquired at the local market, I made quick blasts of air to blow off the dust particles.    It seemed to work!

As the sun set, I positioned myself to take pictures of the rapidly darkening sky toward the east.  I managed to take a few exposures according to my prescribed time schedule and exposure guide, but got distracted by the very young moon to the west.  I abandoned the experiment in favor of the beautiful scene behind me.

The nearly invisible sliver of a one-day moon.

With the sun having set, but the sky in that limbo between civil twilight and astronomical twilight, (dusk and dark), I went to the nearby Goulding’s resort and enjoyed dinner, hoping that the clouds and wind would go away while I refueled.

The clouds dissipated, but the wind continued.  When I returned from my dinner break to the campsite (that I had booked for another day), I decided that I should try and find a windbreak so that my telescope would be protected from the image-blurring gusts.  It was a short hike to the visitor center, where I found a position on the veranda behind one of the walls where a relative calm protected my tripod.

During the next six hours I was able to take a number of astrophotos through the telescope.  The residual wind was still a hassle, finally dying down after 1:00 am.   I had two targets, the Orion Nebula and the Cone Nebula.  Unfortunately, my tracking skills, even in the reduced wind gust, were not up to the task, and I would later find that the exposures were not stable enough to work with. Nevertheless, it is always good when one can practice the art.

Meanwhile, during the time I busied myself with the details of making these exposures, I had set up my film cameras to record even longer durations.  They yielded lengthy star trails over the monuments, which are really only a blip of time compared to their geologic history.

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Monuments at Night, Nov 2

San Juan River Goosenecks, UT

In exchange for the aborted photo session, I enjoyed a full night of sleep and awoke recharged and ready to further explore the area.  After last night’s efforts, I recognized a few more things I am in need of:  AA batteries (of course), a blanket or tarp, and a stool, adjustable, for help while guiding the telescope at awkward positions.  I also needed to fix the too-tight declination gear on my telescope mount.  I noticed that there was dust on my digital camera sensor; I needed something to blow it off.  These are things I should be able to accomplish during the daytime hours while doing reconnaissance for my next nighttime excursion.

I headed north, back toward Monument Valley, this time looking for viewpoints with north-facing vistas, but all the interesting compositions seem to be east of north.  I continued, past the visitor center and campground, and then past the iconic bluffs into Utah.

Here I found Gooseneck State Park, a flat empty span at the top of a huge canyon of the San Juan river, which made meandering oxbow cuts into the mesa.  In the distance, the monuments I had left behind were visible on the horizon. 

At this pleasant site, I set up my telescope and mount and performed the fine-tuning needed to correct the misalignments from the bruises and bumps during travel.  I also corrected a guide mirror which I discovered I had installed backward.  I aimed the telescope at the distant monuments.  In this view they looked like Stonehenge.

Monument Stonehenge, the telescopic view.

The forecast was not encouraging, and on the way back I saw the buildup of clouds.  Still, the scenery was spectacular, and at sunset there was a momentary break in the clouds that allowed a nice silhouette. 

Sunset, returning to Monument Valley

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