CCD Astroimaging Basics

HEART OF THE SYSTEM, THE CCD CHIP

The image sensor in a CCD camera is the CCD chip. These range in size from 2 to 3 millimeters on a side for the less expensive cameras to 2 inches or more on a side for the latest generation of professional chips (great if you have a budget of several hundred thousand dollars). The chips contain arrays of pixels (light sensitive spots) from appx. 128 x128 pixels up to appx. 2048 x 2048 pixels. The pixels themselves range in size from about 6 microns to about 30 microns. CCD, by the way, stands for charge coupled device.

HOW DOES IT WORK?

The CCD camera is mounted on the back of a telescope (or even a camera lens) and the image formed by the optics is projected onto the chip. Light striking each of the pixels on the CCD chip is converted to electric charge. This charge is greater where there is more light and less where there is less light. At the end of each exposure, the charge on each pixel is read by the computer and the picture is formed. During this exposure the telescope must track the stars VERY precisely. In fact, the most important part of CCD imaging is a good telescope drive.

WHAT KIND OF CAMERA DO YOU USE?

I have used five different cameras, most made by Santa Barbara Instruments.

The cameras I have used are:

You will notice that the pictures taken with the larger chips have a more "photographic" look to them due to the larger number of pixels used for a given object.

HOW ARE THE IMAGES PROCESSED?

The images are collected and the camera controlled using MaxImDL. The images are usually processed using PhotoShop and MIRA A/P, two very advanced astronomical image processing programs made by Adobe and Axiom Research, respectively. Most basic processing and image enhancement are done with these programs. Once this processing is done the images are converted into .TIF format and processed for the web page or printing using Adobe Photoshop. I also use Ray Gralak's "Sigma", RegiStar, PixInsight LE, as well as a couple basic programs that I wrote myself.


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