By Patricia Daukantas

Imagine standing in New York and being able to peep through a telescope at people walking down the street in London. Or the other way around.

Nonsense, you say. The magnification required for such a ground-based telescope would be daunting. And then there’s the little matter of the curvature of the Earth over the 5,580-km distance.

However, a British artist has been able to build such a “telescope”—and even to make his creation look like a giant tube that was drilled through the Earth from one coast of the Atlantic Ocean to the other.

On May 20, the public-art project emerged from the banks of the East River in Brooklyn as a giant metal drill bit. By Thursday, the art installation looked like the end of a giant brass and wood telescope poking out of the ground. This “Telectroscope” is Paul St George’s conception of a 19^th-century idea that started when a reporter misspelled the word “electroscope” (a classic device for measuring static electricity) and writers such as Mark Twain spun tales of pictures that could be sent around by telegraph wires.

Although the “story” on St George’s Web site, telectroscope.net, implies that a giant straight-line hole was drilled through the Earth, the gizmo really relies on high-definition cameras linked by undersea fiber-optic cables, courtesy of the European Internet provider Tiscali.

Still, the Telectroscope gives passersby the illusion that they are looking through a giant Victorian spyglass—and they can actually wave at their counterparts on the other side of the Atlantic.

CNN and the New York Times are among the media outlets sorting out the colorful facts and fiction about this artwork, which will be in operation in both London and New York until June 15. The Telectroscope fits in well with other “steampunk” movies, novels and fashions that have gained popularity in recent years.

By Patricia Daukantas

You’ve seen her portrait: the doelike eyes, the Mona Lisa smile, the jaunty feathered hat tipping down over a bare shoulder. Since the early days of computer networks, her image has become one of the standards for image calibration, manipulation and transmission within the optical imaging community. Her portrait has graced hundreds of image-processing papers over the past 36 years and will doubtless contribute to many more. But who is she, and where did she come from?

Her name is Lena Sjööblom Söderberg, and today is her 57^th birthday. The head-and-shoulders portrait of Lena (sometimes spelled “Lenna” in English) is cropped from a far more revealing image in the November 1972 issue of Playboy magazine. Researchers at the University of Southern California created a digital file of the picture as an alternative to the more boring test patterns of the era. As the former editor-in-chief of an IEEE journal once noted, the photo has a good mix of details for testing image-processing algorithms – and her face had a certain appeal to the then-mostly-male research community.

It took many years for Lena to learn that her face had helped bring about the JPEG and MPEG standards and other imaging technology that we take for granted today. Since her days of modeling in Chicago, she returned to her native Sweden, married and had three children. Various Internet sources have her working either for the Swedish national liquor monopoly or as a teacher of computer skills to adults with disabilities. According to one of Lena's fans at Carnegie Mellon University, she was a special guest at a 1997 conference of the Society for Imaging Science and Technology.

By Patricia Daukantas

If you’ve watched TV lately, you may have noticed an ad from a domestic beer company that made an extraordinary claim involving lasers. The company said it would project its logo on the near side of the moon during its full phase last Friday.

It didn’t take much Googling for me to debunk the “moonvertising” plan as a hoax dreamed up by an advertising agency team. But it raises a fascinating question: Is it possible to shine a laser beam onto the moon and see the light from Earth?

One entertainment executive says that a soft-drink company had similar moon-lighting plans for New Year’s eve in 2000, but the Federal Aviation Administration nixed the idea out of concern for aviation safety. Although the executive claims that scientists had done the math and found that such a feat was possible, he doesn’t present the research to back up the claim.

So I asked Tony Campillo, OSA’s senior director of science policy, to work out some back-of-the-envelope calculations. Tony has more than 40 years of experience in optics and photonics, as both an optical scientist with the Naval Research Labs and other institutions and as the former editor of the journal Optics Letters. His verdict: Making a light spot on the moon that people could see without assistance would likely require continuous laser power beyond anything we have on Earth right now.

Let’s imagine a single beam of green laser light originating on Earth’s surface and aimed at the moon. (The human eye is most sensitive to light of about 555 nm in wavelength, and green just happens to be the favorite color of the beer company that started this whole thing.) Assume that the outgoing beam is 3.5 m wide, as in the Apache Point Observatory laser-ranging program. After atmospheric distortion, the beam width would be 2 km at the moon, and about 90 percent of the light would reach the lunar surface.

But wait! The moon reflects only about 10 percent of the light that hits its surface. And even that, according to Tony, is scattered into a Lambertian pattern that covers an area that is 100 times the size of the Earth by the time it returns.

We know that the light-gathering part of the human eye—the dark-adapted pupil—is 1 cm wide at best, and let’s make a rough assumption that the diameter of the scattered beam is 1 million km wide when it hits the Earth. Thus, the naked-eye observer is catching only about 1 photon in every 10²².

How much light is needed for the human eye to see? In other words, what’s the threshold of human vision? I know more about astronomy than biology, so I’m a little shaky on that answer. Although some say that, in principle, the human eye should be sensitive to single photons of visible frequencies, in practice noise from both the visual field and the observer’s own neurological system gets in the way. Astronomers must subtract out background light when they are trying to measure the brightness of heavenly objects with their telescopes.

In Optics InfoBase, I found a 1919 (!) report by P.G. Nutting, OSA’s very first president. On the next-to-last page of the 25-pp. document, there’s a table that provides visual detection thresholds for sources of various areas; for the smallest source, the threshold light energy is 17.1 × 10^-10 erg/s, or 0.17 femtowatt (fW). (You could quibble that the table heading should be “power entering eye” instead of “energy entering eye” because the erg is the CGS unit for energy, not power. However, maybe unit accounting was different in 1919.)

Tony also guessed that an input of at least 1 fW from a continuous-wave (cw) laser would be needed to trigger sight in the human eye. Extrapolating to the originating laser, he guesstimated that a 100-GW cw laser would be needed to produce a visible spot on the moon.

Another way of thinking about the sensitivity of human vision involves the astronomers’ system of apparent magnitudes for measuring the brightness of objects in the night sky.

The apparent-magnitude scale is a logarithmic scale dating back to ancient days. The faintest stars that the human eye can see have a magnitude of 6, while stars with a magnitude of 1 are 100 times brighter than their 6^th-magnitude cousins. Nowadays, you might still be able to see 6^th-magnitude stars from a high desert on a clear night. However, from the typical suburb of a brightly lit American city, you would probably see only 3^rd-magnitude and brighter stars.

Suppose that the brightness of the one-pixel lunar display is 1^st magnitude. With the assumption that the pupil of the dark-adapted eye is 7 mm in diameter, Tony calculated that the eye will receive 200 photons/s from a 6^th-magnitude star and 20,000 photons/s from a 1^st-magnitude star. According to Tony, 1 W of green light corresponds to 2 × 10¹⁸ photons/s. By this line of reasoning, 0.01 fW of light from a 1^st-magnitude star hits the retina, and thus only a 1-GW cw laser would be required to make a visible dot on the moon.

In this case, Tony adds, his estimate assumes that the laser is painting a single 1^st-magnitude pixel on the darkened portion of a first-quarter or last-quarter moon. The beer commercial calls for shining an image on the full moon, which would require a lot more energy.

How does this estimate compare with existing lasers? The petawatt laser-fusion projects at the University of Rochester and Lawrence Livermore National Laboratory will generate huge energies – but over pulses in the nanosecond to picosecond range, not cw.

What would it take to build and fire a 100-GW cw laser? My best guess (from U.S. Energy Information Administration data) is that the United States generates roughly 4,000 GW of electricity every hour, but I could be way off. Would it really take 2.5 percent of the U.S. electrical supply to make a visible green dot on the surface of the moon?

Here’s where you come in. We’d like to ask for your feedback on our calculations and estimates. Many of the assumptions that Tony and I have made need to be refined, especially the size of the Lambertian scattered beam returned to the Earth. A better calculation of that beam size would have to take into account the cosine-square nature of the scattering to estimate the peak flux; that could change the guesstimate by an order of magnitude or more. Some questions to ask yourself:

§  What is the threshold at which a human on Earth could detect a bright spot on the moon? What is the optimal size of a pixel on the moon?

§  How much different would the experiment be if the bright spot was on the face of the full moon (which has an apparent magnitude of roughly −12) or a darkened region of the moon (between the quarter-moon and new-moon phases)? What is the required pixel brightness in each case?

§  What kind of a laser would be required to make this stunt work?

§  What would be the technical challenges involved in making such a laser?

Once you’ve tackled these yourself, you might pose these questions to your students as a thought experiment.

If any of your friends mention that they were disappointed about not seeing a logo on the moon, at least you’ll be able to explain why.

Image of the near side of the moon taken by the Clementine mission.

Posted by Christina Folz, OPN Managing Editor

Last Sunday night, the CBS news program 60 Minutes ran a fascinating story about a non-lethal “ray gun” that the Pentagon has developed. The weapon is a flat-dish antenna that shoots a 100,000-watt electromagnetic beam of high-frequency radio waves, hitting anything in its path with an intense blast of heat. Unlike in Buck Rogers, however, the beam is invisible unless viewed with an infrared camera. It does not inflict any lasting damage and just barely penetrates the body’s tissues. (It is absorbed only in the top 1/64 of an inch on the skin, which is where the pain receptors are located.) The weapon is chiefly intended as a crowd-control device. 

The report reminded me of Steve Wilk’s March 2005 Light Touch article in OPN about “How Ray Guns Got their Zap,” which describes the real science behind the ray guns used by fictional heroes Flash Gordon and Buck Rogers. The article explains the origins of the word “ray” and how it came to refer specifically to directional electromagnetic radiation.

By Patricia Daukantas

My first camera was a Polaroid—back when the “colorpack” film had the peel-off chemical paper. I think it was a Model 320; it had bellows. The camera was the best Christmas present I got when I was 12 years old, and I immediately started taking pictures of my parents and grandmother. Letting the print-negative sandwich dangle from my fingers for exactly 60 seconds, then peeling the thing apart and setting the print to dry without getting chemicals on my skin, became a test of my ability to handle grown-up technology.

Of course, a year or two later, Polaroid Corp. came out with the first SX-70, and people didn’t have to fiddle with timers and smelly trash anymore. But those cameras were expensive, so I labored with my older Polaroid for a few more years until I got a hand-me-down Kodak camera from my father. Finally, I took up 35-mm photography in college.

Now comes word that Polaroid—or what’s left of the company after a bankruptcy several years ago—is discontinuing its remaining instant-film products. The company is willing to license its technology to other companies who might want to supply the ever-shrinking niche market for the instant-developing film. However, if no firms come forward, the remaining Polaroid devotees will be out of luck.

As the New York Times recounts, the self-developing Polaroid prints seemed like a wonder back in the days of film photography. And instant photography has a major connection to OSA history: As noted in the February 2007 issue of OPN, Polaroid founder Edwin H. Land chose the 1947 OSA annual meeting to demonstrate the technology for the first time. He was the hit of the OSA banquet, which took place the same month that his JOSA article was published explaining the process.

Legend has it that Land was inspired to develop instant photography when his daughter asked him why she couldn’t see the pictures he took immediately. Today’s children, surrounded by digital cameras, will never think to ask that question.


 
Polaroid Land Camera 360

By Patricia Daukantas

The popular rock band U2 made its first concert movie two decades ago. So why are film critics falling all over themselves to rave about its second movie?

The answer, it turns out, lies in optical imaging technology. The directors of “U2 3D,” which opened recently in limited engagement, used special 3D digital cameras from 3ality Digital Inc. of Burbank, Calif., to film the live-action concerts.

As reported by Wired.com, each of the 3ality mobile camera setups—there were nine in all—incorporated two Sony digital cameras, surround-sound recording equipment, and an unprecedented degree of computer control of the cameras and zoom lenses. The cameras generated incredible amounts of data, which fiber-optic cables fed into 3ality’s servers for editing and post-production. (The finished film contains almost 1 petabyte of data—that’s as much as 1 million 1-GB USB drives.)

More information is available on the movie's Web site—but check your computer’s speakers before surfing there, as the home page features Bono’s voice singing the opening of the song “Vertigo.”

By Patricia Daukantas

When New York’s Rockefeller Center Christmas tree burst into glorious colors on national television last night, the brilliant light came from energy-saving LEDs for the first time ever.

Until this year, incandescent bulbs had always lit the giant tree, which has been a Big Apple tradition since the 1930s. However, the 2007 tree, an 84-foot (25.6-m) Norway spruce, is strung with 30,000 LEDs on 5 miles (8 km) of electrical wire. For each of the 42 days that the tree is illuminated, it will consume 1,297 kWh of electricity instead of the 3,510 kWh used by the old-fashioned bulbs. The difference is enough to power a 2,000-square-foot (186-m²) single-family home for a month.

According to New York municipal officials and the Rockefeller Center management, the “green” tree is part of an environmentally oriented package that includes installation of a 363-panel photovoltaic roof that feeds into the electrical grid of the building complex. The roof will power the tree during the holiday season, and when the tree is taken down in January, the wood will be cut up for use in Habitat for Humanity homes.

With energy prices at record highs, more manufacturers are starting to produce LED holiday lighting for home use, too. Not only do LEDs save caboodles of electricity, but they last up to 100 times longer than conventional bulbs. If you’ve ever spent a December afternoon wrestling with a long string of series-linked incandescent lights, trying to figure out which bulb blew out and made the whole string go dark, you’ll appreciate the long lifetime.

Nevertheless, LED lights still cost more than their old-fashioned counterparts, so it may take a family a few seasons to recoup the cost.

For photos of the tree, check out this photo gallery from the New York Daily News.