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Low-Light-Level Cameras Now Bring Heavenly Happenings Down to Earth.

While low-light-level cameras have become widely accepted for electronic surveillance of poorly lighted hallways, stairwells and parking lots, they are also gaining fast popularity as a means of surveying the heavens.

Professional and amateur astronomers across the country are rapidly discovering that low-light-level cameras provide excellent resolution of stars and other celestial happenings that, until now, have been difficult or impossible to detect. The camera chosen by some stargazers is the I-SIT (intensified silicon intensifier target) camera from RCA's New Products Division

Clyde Tichenor writes in a recent issue of Sky and Telescope of his experiments with an RCA TC1040/HRO camera at the Polaris Observatory Association's dark-sky site in Lockwood Valley, California: "The unit turned out to be the best camera I have ever used."

John Mosley, program supervisor at Griffith Observatory in Los Angeles, is also experiemnting with the I-SIT camera. The observatory has recently purchased one for a variety of uses, including providing feeds to local television stations.

Initially, the camera will be used to capture actual real-time footage by photographing images in the observatory planetarium. This real-time footage will then be edited to simulate celestial events such as en eclipse or meteor shower.

Mosley says this technique will be used to re-create a variety of events, including the positions of the planets, showing the Star of Bethlehem, at the time of Christ's birth.

Another early use for the camera will be video taping comets and metero showers under the night sky. Mosley explains why they choose this camera for that purpose, "Because the skies are very polluted in Los Angeles, we needed more light grasp in bad-viewing situations. We hope in the near future to be able to beam direct celestial images onto the museum monitors, so that large numbers of people can view them during special events."

Since the observatory is visited by approximately two million people per year, this low-light-level exposure could enhance the celestial knowledge of a sizable population segment.

The observatory is using a TC1040/H camera with a 10X zoom lens. This high-performance model can provide a light range up to 32 billion:1, depending on the "T" of the auto-iris lens. Plans are also in process to attach a 4-foot aluminum mount assembly via a mounting plate at the rear of the telescope. The mount would be convertible so that a field lens could be used to send magnified images into the system.

One member of the observatory team that has worked with the camera says, "When we tested the camera with our star projector in the planetarium theater, we were in complete darkness, with the stars almost off. The camera was so sensitive to light that we could see with it what we couldn't see with the naked eye. It even picked up the image of our black star projector."

In Phoenix, the Sagurao Astronomy Club was looking for a better was to clearly see the stars. So Bill Mayfield, of C.T. Carlburg & Associates, Scottsdale, loaned them an RCA TC2011 Ultricon camera and a TC1109 black-and-white monitor to try on their next stargazing venture. The camera was attached to an 8-inch reflector telescope and interfaced with a microchannel plate image intensifier.

Mayfield explains what happened: "Their original objective was to sight in onsome of the fainter stars, but, to their surprise and excitement, they inadvertently focused on a ring nebula and received outstanding resolution."

Pete Manly, club president, goes into further detail. "We had been working some calibration stars near the celestial equator, and I decided to swing the telescope to the zenith to obtain minimum background light and check performance in darker backgrounds. We all knew that the ring nebula was near the zenith, and decided to search for it after we got some dark-background readings. We just happened to put the telescope on it without any precision pointing. The surprise was that we could see it clearly. As part of our planned test of the camera Mayfield loaned us and another one owned by a club member, we had intended trying for nebular objects later in the evening. We just weren't aware that it would be so easy to see them."

As a result of the camera's excellent performance in the field, the club has purchased two models of the low-light-level camera. These units provide automatic beam control, auto-track electronic focus, high resolution, and output level control.

Manly says the camera captures faint images so clearly that recnet Perseid meteor shower footage, taped by the club, was deemed suitable for broadcast on KPNX-TV in Phoenix. He adds, "We have reviewed the tapes and found many very faint meteors. This was an unexpected bonus, since naked-eye observers did not see these meteors at the time of the observation. The meteor observations were made with a wide-field lens on the camera instead of a telescope." The Units Are Taken to Local Schools

The club, composed of 160 amateur astronomers, intends to use its cameras for monthly observing sessions and for special sessions involving asteroid and lunar occultations (eclipses). The units are also being taken to local elementary schools so students can view celestial activity firsthand.

Dr. Alan Fiala, staff astronomer in the Nautical Almanac Office at the US Naval Observatory in Washington, DC, has taken an Ultricon camera all over the world to video tape solar eclipses. He explains the purpose of his missions is to determine if the sun has a detectable variation in its energy output. His expeditions include observing and video taping rapidly occurring faint-light events as the moon and sun move into and out of alignment. The data is then used to determine the sun's diameter at the eclipse.

Recently returned from his latest camera work in Indonesia, Fiala says, "We finally got a decent, permanent record for objective analysis. We have decided that this is the tool we need. It's even more sensitive than the human eye."

Prospective low-light camera buyers are advised to first set their specs and performance requirements before deciding on a specific model. A critical factor in choosing the right camera is the environment in which it will be used. Camera sensitivity--the response of the camera's tube to light--is the key.

While there is no standard nomenclature on this subject, some suppliers classify cameras as twilight, moonlight and starlight types. If one does not select a camera based on proper sensitivity, one won't get the pictures expected.

Potential buyers should also consider the source of light under low-level conditions. Mercury vapor, sodium vapor and incandescent lights all differ in their light outputs' spectral characteristics. Mercury vapor light, for example, is predominantly blue and green with very little red. Thus, a standard camera rated for incandescent light will have considerably less sensitivity when observing a scene lighted by mercury vapor lamps. Sodium vapor, on the other hand, provides a somewhat broader spectral distribution than mercury vapor, but still lacks the red and infrared available from tunsten light.
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Publication:Communications News
Date:Jul 1, 1984
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