Cookbook CCD Camera

I'm currently working on assembling a Cookbook CCD Camera, as described in the book by Richard Berry. The camera will be used with my Celestron C8 telescope to take astronomical images. I am building the CB245 version - one of two cameras described by the author.

Camera Head

I purchased the camera head from University Optics, since I don't own the lathes and milling machines that are required to construct it.

Printer Port Interface Board

The printer port interface is the most complex part of the camera. It connects the computer to the camera, via the parallel port. Here's a picture of the printer interface, just before I inserted the IC's:

CCD Pre-Amp

The CCD Pre-Amp increases the strength of the signal generated by the CCD chip. The printed circuit board is mounted on the camera head, because otherwise the signal would be become so attenuated by even a few inches of wire that the images would become unusable. Once the signal is boosted by the pre-amp board, it is strong enough to pass through a few feet of parallel cable to the Printer Port interface board.

Power Supply

The CCD Camera Cookbook describes the construction of a power supply. I chose, however, to use a commercial power supply. Eventually, I decided to use a Power-One model CP131 supply. There are numerous advantages to the CP131; It is much lighter than any supply that I could reasonably build, it has built-in protection circuits that the power supply in the book lacks, and it looks nice, too.

Cooling System

Unlike conventional digital cameras, CCD cameras that are used for making astronomical images must use exposures that last for periods of time ranging from a few seconds, to several minutes long. Why is this so? Because the camera must gather as much light as possible from extraordinarily faint objects. The longer the exposure, the more light that can be recorded.

However, CCDs have a property that limits the length of an exposure. When the CCD is exposed to a light source, then "dark current" starts becoming an issue. Essentially, dark current causes randomly distributed pixels on the CCD to become active, which shows up in the image as a bright speck. The impact of dark current can be reduced by cooling the CCD to lower temperatures. In my Cookbook camera, I will be using a peltier cooling device, and a five-gallon bucket of water to cool the CCD to about -25 degrees Celsius. While it is possible to reduce the temperature of the CCD even further, it wouldn't be of much practical use, since my exposure time will most likely be most limited by the inaccuracy of the motor drives on my telescope mount.

Progress

September 5, 1999

So far, I have completed the Interface Board, and have made up most of the cables. As mentioned above, I already have purchased the power supply, which will cut my construction time down by ten hours or so. At this point, I still need to complete the pre-amp board, and the camera head.