The CCD Camera


The camera and software used to acquire the images of scattered light is a critical element of the whole apparatus. The scientific CCD camera used was the EDC-1000N made by Electrim Corporation in Princeton, New Jersey [9], which records 652x494 monochrome pixels. This camera was selected for general use in the optics laboratory where I did my work after a careful consideration of the needs of my experiment and others. Cost was a significant consideration in the choice of camera. Scientific CCD cameras often cost $10,000 or more (and the camera used by Hielscher etal, at Los Alamos cost twice that much [10]), while the EDC-1000N cost only about \$800 and could operate quite happily from an ``obsolete'' P166 computer that had been donated to the optics laboratory. The relatively low cost is explained in part by the fact that the Electrim camera is unusual among scientific CCD cameras in not having the CCD element cooled. Cooling greatly decreases ``dark noise'' and is essential in astronomy and other low light-level applications. The exposures times for the current experiments are quite short (a few milliseconds) however, and cooling isn't essential.

While not suitable for low-light experiments, the Electrim camera does fulfill all of the other requirements for this project and others in progress at the optics laboratory where this research was done. Our purposes required an anti-blooming feature to help prevent CCD ``wells'' from overflowing into neighboring ones, which could cause misrepresentation of intensity in the final images. The exposure time had to be easily adjustable over a wide range, as we were unsure what timing would be appropriate for the backscattering images. It was also preferable that the camera be directly connected to the computer (rather than through a parallel printer port) for faster data transfer speed.




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