The Telescope

ubble's "workhorse" instrument — the Wide Field and Planetary Camera 2 (WFPC2) — is behind most of the famous Hubble pictures. WFPC2 is the telescope's main camera. It observes just about everything, recording razor-sharp images of faraway objects in relatively broad views. Its 48 filters allow scientists to study precise wavelengths of light and to sense a range of wavelengths from ultraviolet to near-infrared light.

No Film Required

WFPC2 doesn't use film to record its images. Instead, four postage stamp-sized pieces of high-tech circuitry called Charge-Coupled Devices (CCDs) collect information from stars and galaxies to make photographs. These detectors are very sensitive to the extremely faint light of distant galaxies. They can see objects that are 1,000 million times fainter than the naked eye can see. Less sensitive CCDs are now in some videocassette recorders and all of the new digital cameras.

From Pixels to Pictures

CCDs are electronic circuits composed of light-sensitive picture elements (pixels), tiny cells that, placed together, resemble a screen-door mesh. Each of the four CCDs contains 640,000 pixels. The light collected by each pixel is translated into a number. These numbers (all 2,560,000 of them) are sent to ground-based computers, which convert them into an image.

Why Do the Pictures
Look So Funny?

The unique WFPC2 design results in the stair-step appearance of many of its images. The "heart'' of WFPC2 is a trio of wide-field detectors and a high-resolution "planetary" camera. Although the planetary camera can see only a small region of the sky, it packs a punch — compacting the same number of pixels into a smaller area results in finer-detailed images. The difference between the wide-field detectors and the planetary camera is like the difference between a wide-angle lens and a telephoto lens.

Hubble's original Wide Field and Planetary Camera was replaced with WFPC2 during the First Servicing Mission in December 1993. WFPC2 was built by the Jet Propulsion Laboratory in Pasadena, California.

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