On page 96 of the July 2004 issue of Sky & Telescope is an article
"King of the Chips: SBIG's STL-11000M", reporting on a camera
intended for mounting on a telescope. This camera costs US $8,000,
is a metal box 15.2 by 16.5 by 8.9 cm, weighs 2.2 kg, draws up to 5
amps at 12 volts, and does full color using a 5-slot filter wheel
(one slot being open, the other four having various astronomical
filters). Santa Barbara Instrumentation Group (http://www.sbig.com)
is a respected maker of such cameras, and sells to the professional
and advanced amateur markets. More advanced than I, for sure.
The camera is based on a Kodak full-frame (35mm) CCD, the KAI-11000M,
which has 4008x2672= 10,709,376 pixels, each 9 microns square:
(http://www.kodak.com/global/en/digital/ccd/products/interline/interlineMain.jhtml)
This is per color, so if this were a photographic sensor with RGB
sensing, it would be 32 Mpix (marketing).
The sensor is thermoelectrically cooled up to 35 degrees C below
ambient temperature. This cooler probably accounts for most of the
5-amps current draw.
A 9-micron pixel corresponds to 1/(0.009*2)= 55.6 cycles (line pairs)
per millimeter, which is comparable to the resolution of photographic
film of reasonable sensitivity to light.
Ignoring dark current (1.5 electrons per pixel per second at 0
degrees C), the dynamic range is Log2(well capacity/read noise)=
Log2(50000/11)= 12.15 bits, although a 16-bit analog-digital
converter is used. Dark current doubles every 7 degrees centigrade,
so at 30 degrees C, dark current will be (1.5)(2^(30/7))= 29.26
electrons per second. In an exposure of 1/30 second, this will be
about one electron per second, and will be lost in the read noise, so
12 bits is still the answer.
The files are uncompressed and huge. Each color yields a file
(10,709,376)(2)/(1024^2)= 20.43 Mbytes long, so for all five "colors"
(filters, actually) it's 102 Mbytes. For three colors, it would be
61.3 Mbytes per picture.
Joe Gwinn
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