The electronic chip in a camera or astronomy camera, made of millions of pixels that turn light into a signal. Its key figures are the pixel size (in micrometres), the sensor dimensions and its noise. Astronomy cameras are often cooled to reduce thermal noise.
Related terms
- Sampling
The angle of sky covered by one pixel, in arcseconds per pixel: 206.265 × pixel size (µm) ÷ focal length (mm). 3.76 µm pixels behind a 500 mm focal length give 1.55″/px. For deep sky, aim for about a third to a half of the seeing (often 1 to 2″/px).
- Gain (ISO)
The amplification of the sensor’s signal, set as ISO on a camera. Raising the gain does not capture more light: it makes the image brighter but reduces dynamic range. A medium to high gain lowers read noise, which helps with short exposures and planetary work.
- Dark frame
An exposure taken with the shutter closed or the tube capped, with the same duration, gain and temperature as the lights. It records thermal signal and hot pixels, which software then subtracts. Usually 20 to 50 are taken.
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