THE HST FOCAL PLANE
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The HST optical system images the sky on to
a location called the focal plane that is just behind the primary mirror. This focal plane
is shared by the five scientific instruments and three fine guidance sensors. The scientific instruments are all placed near the center of the focal plane, where the optical distortions are smallest. The fine guidance sensors are located around the periphery of the focal plane. These instruments maintain HST's accurate pointing to better than 0.007 arcsec while scientific data are being collected. One consequence of this arrangement is that the instruments cannot all view the same part of the sky simultaneously. The WFC3 occupies the central portion of the HST focal plane, a section that has a relatively large field-of-view and which has minimal optical distortion. A large field-of-view allows for simultaneously capturing the light from a large portion of the sky, while the low distortion simplifies the optical system of the instrument.
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Page Last Updated: March 16, 2001
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