Light Spectrum

The Wide Field and Planetary Camera 2 (WFPC2), removed from the telescope in mid-2009 to make way for Wide Field Camera 3, was behind many famous Hubble pictures. WFPC2 was Hubble's main camera until the Advanced Camera for Surveys was installed in 2002. It observed just about everything, recording razor-sharp images of faraway objects in relatively broad views. Its 48 filters allowed scientists to study precise wavelengths of light and to sense a range of wavelengths from ultraviolet to near-infrared light.

No Film Required

As with all of Hubble's current instruments, WFPC2 used electronic detectors, not film, to record its images. In WFPC2's case, four postage stamp-sized pieces of high-tech circuitry called Charge-Coupled Devices (CCDs) collected information from stars and galaxies to make photographs. These detectors were very sensitive to the extremely faint light of distant galaxies. They could see objects 1,000 million times fainter than the naked eye can see. Less-sensitive CCDs are now used in all 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.


Wfpc2 Install

Installation of

Why Do the Pictures Look So Funny?

The unique WFPC2 design resulted in the stair-step appearance of many of its images. The "heart'' of WFPC2 consisted of four cameras: one high-resolution "planetary" camera and three "wide-field" cameras. Although the planetary camera could see only a small region of the sky, it packed a punch — compacting the same number of pixels into a smaller area resulted in finer-detailed images. The difference between the wide-field detectors and the planetary camera was 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.