by astro_uk » Wed Aug 30, 2006 10:11 am
Hi matthijs
The effect is called bleeding, its when charge in the CCD bleeds up and down columns and across rows when the target saturates the detector. In other words the brightest pixel in the centre of the star image cannot hold any more electrons (which are released by the light impinging on the chip) so the charge tends to fall down the rows and columns. They can generally be removed by taking more shorter exposures so that the central pixel does not saturate. However if pretty pictures are not the main driver (and generally they arent) then they dont tend to cause too many problems so its easier not to break up the exposures.
Hi matthijs
The effect is called bleeding, its when charge in the CCD bleeds up and down columns and across rows when the target saturates the detector. In other words the brightest pixel in the centre of the star image cannot hold any more electrons (which are released by the light impinging on the chip) so the charge tends to fall down the rows and columns. They can generally be removed by taking more shorter exposures so that the central pixel does not saturate. However if pretty pictures are not the main driver (and generally they arent) then they dont tend to cause too many problems so its easier not to break up the exposures.