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Hubble Space Telescope
Super Shading

NIC1 - F113N
NIC2 - F212N
NIC3 - F166N

"Supershading" appears to be a change in the observed shading curve when the array is fully illuminated (e.g. by a bright calibration lamp or the Earth when taking Earth-flats). This effect is little understood, but is likely associated with the electronic ghosts seen when observing bright point sources. It is possible that "Supershading" is the same effect, seen over the entire array. Whether the underlying cause is the large rate of charge passing through the amplifier, or the associated heating of the amplifier or some other mechanism is currently unknown. This effect has serious implications for creating accurate flatfields and for measuring pixel gain and linearity.