Reflections in the Eyepiece, October 1990

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Last touched 2001 December 4

Originally published in M-111, the Newsletter of the Richland (Ohio) Astronomical Society

Reflections in the Eyepiece

November, 1990

Robert Bunge

During past couple of years I've heard a good bit of talk about the future of amateur astronomy. A year or two ago, it was about computerized telescopes that point the instrument to the right part of the sky without manual asistance. Some people suggested that most all future telescopes would have this function (Even though not all people would use it).

Another mention I've heard is how much data is becoming available to amateurs. With the advent of huge databases like the Hubble Guide Star Catalogue on Compact Disc along with the number of amateurs who own computers (50 percent of Sky & Telescope's readers own a computer) there as been conjecture that amateurs will start to do more research (Only 2 percent of ASTRONOMY magazine's readers say they are interested in doing research).

Most recently it has been hard not to notice another new technology rising to the front that seems to offer interesting possiblities. It's the Charged Coupled Device, or CCD. CCDs operate some like film, something like video cameras and something like photometers.

They promise to be a boon to amateurs interested in research, offer new, creative ways to astrophotographers and supply the average, high-tech oriented amateur astronomer with a new tool to figure out.

I was going to talk about how a CCD works, and some of the basic dealings about them, but an article in the October issue of ASTRONOMY magazine does exactly that. And does it much better than I could with my limited experence.

My first contact with a true CCD camera occured about a year in the dome of the 12-inch Alvan Clark refractor at the U.S. Naval Observatory in Washington D.C.. USNO had just taken delievery of a new camera for use at the D.C. station, and it was their first chance to use it.

Former RAS member Brent Archinal had invited me along. The group of observers (who had actually read the instructions before trying to use it!) managed to get some nice images of M-42 on the screen... impressive because most everything was jury-rigged at the time.

Last month, I had another chance to see the same CCD in action during a visit to the USNO. Brent's offer to go observing caught me by surprise. It was almost full moon out, and observing was the last thing on my mind. But, Brent commented that with the lights of D.C., the moon only made a little difference and it was a good chance for him to show off the toy.

USNO's "toy" is not your average CCD which are appearing in advertisments in the magazines. It is a Photometrics camera equipted with a Thomson 1024 by 1024 chip. The cost of the camera was about $70,000, of which $20,000 was just for the chip. "Amateur" CCDs run as low as $400 (Without computer) and as high as $3,000 (still without computer). The difference in price has everything to do with the chip that is in the camera.

The 1024 by 1024 refers to the number of pixels, or light gathering points, in the chip. The more, the better (The CCD on the Hubble Space Telescope is 800 by 800). If you have more pixels, the chip is physically larger and the resolution is higher. The low cost amateur chips have 192 by 165 (notice this the same proportion as an IBM computer screen) pixels and are only 2.6 millimeters on a side. Even the big chips are small. The Thomson chip is about a quarter inch square.

At USNO, they can mount the camera on either a 7-inch F/9 Astrophysics refractor or a 24-inch F/13.5 Boller and Chivens Cassigrain reflector. The night I was there, the 7-inch had just been piggy-backed on the 24-inch that same day, so the camera was at the 24-inch telescope's prime focus. The mounting and drive on the 24-inch is good enough that they can take up to a two minute exposure without having to guide.

Because of their nature, CCD chips tend to be pretty sensitive in the infared part of the spectrum. USNO's chip had also been coated to make it sensitive to some ultra-violet light.

When we arrived, one observer was already there, taking images of variable stars. Lesson number one about CCDs. They are great for collecting data. Each pixel in the USNO camera can record up to 16,000 levels of light. Amateur CCDs can record at least 255 levels. This means they can be used a lot like a photometer and can be used to measure magnitudes of stars, galaxies and other objects.

Lesson number two. Because of this, one needs to think of CCDs as having depth. Not only do they have width and height like film, but because of their ability to record levels of light to a VERY accurate level, creative people who can think in new ways will recognize this and design their observing projects to take advantage of it.

You can sort of think of it like a house that has been painted over and over with different colors. If you take a piece of the siding off, you can look at a cross section and see what color the house use to be. With a CCD image, you can have a computer look at the cross section of the image and strip away the layers that you don't want.

Ok, so you ask, "So what?" It means that people used to doing things a certain way may not use a CCD to it's full potential. It also means the people who you might think would have the best equipment to use CCD's -- astrophotographers -- may tend to treat them like a new type of film and not explore this new domain.

Another thing about CCDs. They're fast! They collect and hold onto the light hitting them in a manner that makes Konica 3200 look like wet emulsion from the 1860's (which had an ISO of about 2). Brent had a H-alpha filter in the light path. This served to help beat the light pollution, but it also blocked out huge amounts of the incoming light.

With the 24-inch, a 30-second exposure from the middle of Washington D.C. and with a full moon in the sky, of M-27 showed MORE detail then the best views of M-27 I've seen with the 31-inch on really good nights.

Ok, you say photography can do that too. Right, but with a CCD, you get instant results. A minute after the exposure, we were examining the image of M-27 that we had just taken on the screen. With a few minutes of image processing, details never seen visually were starting to jump off the screen and running across the floor.

So now, if you place the tiny CCD chip at the prime focus of a small, fast newtonian -- say a 6-inch F/5 -- all of a sudden you can start observing clusters of 15th magnitude galaxies that before you could only see with something like the 31-inch. (Just think what something like the 31-inch could do!).

Some people (like me) will cry, "That's not TRUE observing... its cheating. "A real amateur sucks those photons in with his eyeball," I once heard Biff Smooter say. Really, there is and always will be something about seeing the object in realtime, without the benefit of even an electronic eye.

Back on the astrophotography front, you don't do the image processing at the telescope. Instead, you "save" it for a cloudy night. No messy, smelly chemicals, expensive paper or houring of guiding. Just walk up to the computer, sit down with a warm cat in the lap and start observing.

But this means that a person has to know computers! Right. That's the bad part... the people who know and have the computers may not have all the fancy astrophoto equipment that can make a CCD hum with photons.

So here we have it. It's not astrophotography. It's not visual observing. It can be very stimulating, but I'm told by people who have done seriously it that it requires an exacting patience and and amount of perseverance that makes astrophotography look easy.

It requires at least some knowledge of computers, a certain amount of capital, but not necessarily dark skies or big telescopes. It does, however, require computers, which in turn require 110 volts, tending to ruling out portable setups.

Perhaps a major point should be that for the first time since professionals started using film, amateurs have access to tools that are similar to the ones professionals have. An amateur seriously interested in doing research can do original research that would make many a professional blush with envy.

In the end, I'm going to predict that we are going to see a new branch of amateur astronomy grow out of CCDs. It may not be a large branch (but then just how many people seriously do astrophotography?) but it will be there.


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