FOC - Eagle Eye


Spectrum 101

Resolution 101



STScI FOC page

European Space Agency FOC page






Faint Object Camera Betelgeuse

Removed in 2002

What Light Does FOC see?



Active galaxy's core
Active Galaxy's core

Opposite hemispheres of Pluto

Globular Cluster
Globular Cluster

The Faint Object Camera (FOC), removed from Hubble in early 2002, functioned during its time aboard as Hubble's "telephoto lens." The FOC recorded high-resolution images of faint celestial objects in deep space, taking the most detailed images over a small field of view. It was replaced by the more powerful Advanced Camera for Surveys.

Pinpoint Accuracy

The FOC's resolution allowed Hubble to single out individual stars in distant star clusters. Resolution is the ability to distinguish two points of light as separate and distinct. In space, the instrument distinguished between objects that were 0.05 arcseconds apart — which is roughly the width of a human hair viewed from a distance of 1 kilometer. If human eyes had this ability, we would be able to distinguish between a pair of automobile headlights 5,000 miles away!

Winnowing Wavelengths

The FOC directed light down one of two optical pathways. The light entered a detector after passing through one or more filters, which permited only specific wavelengths of light to pass through. By selecting very specific wavelength ranges, scientists could look for specific features, such as the hottest stars in a particular cluster.

The detector intensified the image and then recorded it, much like a video camera. Images of faint objects were built up over long exposure times. The total image was converted into digital data, transmitted to Earth, and then reconstructed.

Since FOC could make high-resolution observations of faint sources at ultraviolet and visible wavelengths, it could study star clusters, examine galaxies and faint objects (such as quasars), and look for small details of celestial objects. The FOC was built by the European Space Agency.

Cool Views from FOC

• Gravitationally lensed quasars
• The actual surface of a star, such as Betelgeuse
• Globular clusters
• Pluto/Charon system