ADU ASTROMETRY FULL

Plot the average ADU of a box of pixels near the center of the sensor on a graph (always use the same group of each pixels from each frame). Howell has a great book that covers CCD characterization, 'Handbook of CCD Astronomy, 2nd Edition'.įor determining the linearity of your sensor you can use an evenly illuminated light source that won't change intensity (you can leave the camera off the scope and face it towards a wall, for example) then slowly increase your exposure time from the minimum until the pixels saturate.

ADU ASTROMETRY FULL

If you want to determine your sensor's characteristics, tools like PixInsight have a simple script (Basic CCD Parameters) for calculating read-noise, dark current, full well depth and gain from some calibration frames, but you can do it your self as well. I don't use Nebulosity, but I think it's safe to say if you've got a 16 bit sensor and you are seeing values from 0 to 65535 those are ADU values. 1/3rd of the maximum ADU) or have calculated their sensors linear range and determined the best ADU value for their particular chip (they do very due to manufacturing process variation). When people say they are using a particular ADU value for their flats they are either using a general rule of thumb (i.e. You want to expose the flat so that it has the longest exposure possible (to get the highest S/N ratio possible) and is still in the linear range of the sensor. This makes the charge buildup in a given pixel non-linear past a certain charge. The reason flats need to be taken at specific ADU values is that most amateur CCD cameras have circuitry to prevent charge spilling over to other cells when they saturate (called anti-blooming). For example, if the full well depth is 100k e- and it is a 16 bit sensor (which has a maximum value of 65535 ADU) the gain would be approximately 1.526 e-/ADU (ADU = pixel charge / gain). Most cameras have their gain set at the factory such that the full well depth charge is approximately equal to the maximum ADU value. Also, the quantum efficiency of a camera is a metric describing how much energy from photon strikes is converted to electron charge in an average cell. The full well depth is a limit to how much charge a cell can hold. The gain of the camera determines the conversion of cell charge to ADU value. it is a digital representation of the electrical charge for a given pixel.

Adu astrometry