Hi,

Are there any digital camera that is well suited for astrophotography? Astrophotography needs long exposure times, several seconds or even several minutes.

-- Allen Chan (Allen.Chan@digital.com), September 02, 1998

Answers

You can get into the several second realm fairly easily, but none of the available digicams are going to get anywhere near the several minute regime. The issue with any of these cameras is that thermal noise in the CCD starts to really dominate beyond a second or so. Fortunately, there's a fairly easy solution to this, using an image editor like PhotoShop. The two cameras I'm aware of that have *really* long exposure times are the HP C20 and the Kodak DC260. The C20 sells for $499, and goes up to 2 second exposure times, while the DC260 sells for $999, and goes to 4 seconds directly from the camera controls, and can be programmed for up to 16 seconds via the scripting language.

At the longest exposure times of both of these cameras, you'll be seeing stars even if you're in a dark closet though: The noise from the sensor gets pretty severe, looking like bad "snow" on a TV set at the longest exposures. Fortunately, this noise is generally what's called "fixed pattern" noise, in that the same pixel will have the same amount of thermally-driven leakage current (and therefore spurious signal) from shot to shot, other conditions being equal (exposure time, temperature, battery voltage, phase of the moon, whatever). This means you can take a shot with black velvet over the lens to get a "black reference", and then just subtract this picture from the one you capture of your actual subject. This can really clean up the garbage to a surprising extent. Another trick you can do (if you have a steady enough guiding system) is to take multiple exposures and average them. This reduces random noise proportional to the square root of the number of images you average together, or by about 30% for two images averaged.

None of the cameras are really going to compete with a dedicated, chilled CCD imager on the back of a telescope, but you may be able to get better results than you'd think at first.

Hope this helps, good luck!

-- Dave Etchells (web@imaging-resource.com), September 02, 1998.