CCDs

Charge-Coupled Devices

1) what CCDs do

in each pixel, a) photons are converted to electrons
b) electrons are trapped & stored in collecting sites

at the end of the exposure, each pixel's

    c) electrons are systematically passed
        (as a unit) to a register
    d) electrons are measured and stored

2) what a CCD image contains

3-dimensional array:

X-position x Y-position x electron count

3) the advantages of CCDs: digital

eye photographic
film photo-
multiplier CCD

quantum
efficiency 1% max,
sharply
peaked
at 550 nm 1%,
fairly uniform across visible 10-20%,
peaks
toward uv 70-90%,
peaks
toward ir

photometric
response logarthmic non-linear linear linear

dynamic range
(I_max/I_min) 10¹⁰
but only
100 at a time < 100 <100 1000-
10,000

geometric
stability good fair exceptional

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	eye	photographic film	photo- multiplier	CCD
quantum efficiency	1% max, sharply peaked at 550 nm	1%, fairly uniform across visible	10-20%, peaks toward uv	70-90%, peaks toward ir
photometric response	logarthmic	non-linear	linear	linear
dynamic range (I_max/I_min)	10¹⁰ but only 100 at a time	< 100	<100	1000- 10,000
geometric stability		good	fair	exceptional