The Wondrous Cookbook CCD Camera

reference:  CCD Camera Cookbook (Berry/Kanto/Munger, Willmann-Bell Inc.)

The camera contains a Peltier refrigerator that requires a constant flow of water. Note hose coupling and heavy wires. I use the old movie projector lens for tests. Not shown is the very dark filter that I have to put over it to keep the camera from getting swamped by ordinary daylight. Like most CBs built from the kits sold by University Optics, this one is customized. You'll still recognize it. I added a tripod socket (in the Lucite), a 1/4"-thick plate to hold the circuit board, and feedthrough capacitors to run out the Peltier wires.

The aperture stop was cut from the sheath of an old 5" floppy disk. You need it because the edge of the entrance opening is shiny and causes a nuisance reflection in all your images. Another useful "mod" are the jacks that allow me to separate the camera from its electronics black box. The driver signals go in via the VGA-type jack. The video comes out on the gold SMB coax jack above the VGA jack.

Here's the Cookbook CCD on the 20-inch Cassegrain telescope at Gordon MacMillan Southam Observatory. On the desk, left to right:  Pentium laptop for the camera's DOS software;  camera power supply;  water tank (donated Coleman cooler) and flowmeter. Clamped to the camera body is a black box containing the A-to-D converter, the PC interface, and some voltage regulators. The Little Giant (tm) pump it has to be underwater to keep it from overheating. So your cooling water heats up undesirably.

My first really interesting CCD image. Supernova SN2005cs was discovered in 2005 by a guy in Germany named Wolfgang. Although the galaxy M51 is millions of light years away, the supernova was so bright that you could see it in an 8-inch telescope. By contrast, all the billions of stars in M51 make just a gentle glow in the telescope. A few weeks after the explosion, the supernova (arrow) was still brighter than millions of stars put together. This is a stack of four 30-second exposures taken on the 6-inch refractor at Southam Observatory.  No guiding was used. If you've ever tried astrophotography, you know what that means.

Asteroid 2004XP14 caused excitement in July 2005 when it flew by the Earth. It came almost as close as the Moon. You could see it drift past the background stars in the eyepiece. When it was closest, XP14 crossed the northeastern sky in only one night. Little XP14 made the trail in this Cookbook image, a 60-second exposure made with the Observatory's refractor. North is up. See the fuzzy star? "Fuzzies" make astronomers very, very excited. Especially when they don't know what they are. I was palpitating! Was it a new comet? Wasn't. Actually, it's the giant variable star BC Cephei. Its temperature is comparable to the red-hot coils on a stove. Most of its energy comes out as infrared light. The camera detected the infrared but the telescope didn't focus it as sharply as visible light. (Same concept as an SLR lens that has a separate focusing mark for infrared film.)

The pixels of the camera are quite big, 20x25 microns when binned 1x3. But on a scope with 8 metres of focal length, that's small. If anything, my images are oversampled. And the camera has only 252x242 pixels. The resulting field of view is tiny (a coupla minutes). So I use a focal reducer. You can buy them, but I'm a cheapskate and I make mine. (The TV camera here has a reducer made from a lens from a scrapped 7x35 binocular. It helps a lot.) For the Cookbook, I use an Elmaron 100mm f/2.8 movie projector lens. I bored a piece of rod to hold it so that its rear principal plane is 50 mm from the CCD. (This is distance D in the formula below). Thus the field of view is doubled (i.e. 4x image area). It has T threads that screw into the camera, and the outer diameter is 2" so it can fit standard drawtubes. (I faked the T threads by cutting 32 per inch. My lathe won't do metric.) When using a scrap lens like this, you orient it in the telescope so that the side that originally faced the near object (slides, eyeballs, etc.) faces your camera. Here, the film side of the Elmaron faces the CCD.

The Elmaron is partially withdrawn to show how it fits inside.  To find the principal plane, rest the lens on a ruler and throw an image of a distant scene onto a block of white material.  Then measure back one F.L. from the image.

You can calculate the optical power of a reducer using high-school math. Use the formula 1/f = 1/D - 1/C, where f is the lens's focal length, C is the distance between lens and telescope's original focal point, and D is the distance from CCD to rear principal plane. Set D to a convenient value (I used 0.5f) and solve for the ratio D/C.