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WFPC The Vault

The Wide Field and Planetary Camera 2 (WFPC2) is the "workhorse" camera for Hubble. It provides us with pictures of the universe on a grander scale than any camera to date. The camera can detect stars over one billion times fainter than we can see with our eyes. This picture shows astronauts removing the Wide Field and Planetary Camera 1 (WFPC1), to be replaced by WFPC2. WFPC2 is shaped somewhat like a grand piano and weighs 619 pounds. The camera records two-dimensional images through a selection of 48 color filters covering a spectral range from far ultraviolet to red wavelengths. WFPC2 has four charge-coupled detector cameras arranged to record simultaneous images in four separate fields of view at two magnifications. The planetary camera provides a magnification about 2.2 times larger than the wide field camera. The planetary camera provides the best sampling of the telescope's images at visible wavelengths and is used whenever the finest spatial resolution is needed.

WFPC2 uses charge-coupled detectors (CCDs) to take data. CCDs have finer resolution, better linearity, and the ability to convert image data directly into digital form. A CCD consists of an array of light-sensitive picture elements (pixels) built upon a thin wafer of silicon. Complex electronic circuits also built on the wafer control the light-sensitive elements. As light falls upon the array, photons of light interact with the sensor material to create small electrical charges (electrons) in the material. The charge is very nearly proportional to the number of photons of light absorbed. The electronic circuits read out the array and send signals that allow the reconstruction of the pattern of incoming light, and hence, a picture.

The CCDs in WFPC2 consist of 800 rows and 800 columns of pixels, equaling 640,000 pixels in each array. Each pixel can be thought of as a tiny square, about 15 micrometers on a side.



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