> Hello list , here is an idle question . > > When one adjusts 'iso' setting on , say, an S2 , what actually happens. > > ie . with film bigger grain accepts light more quickly (I think) , > hence fast film being grainy and slow film having finer grain. > > So how does that work on a ccd ? in simple english ? Cos we have > noticed 'grainier' shots at higher iso settings , which doesnt make > sense to me. > > yours , confused > > Janus
In hopefully not to technical a way... With normal ccd sensors the amount of electrical charge that is generated in each pixel is proportional to the amount of light it receives. It is this charge that measured and produces the 'output' for each pixel. The amount of noise (random fluctuations in charge) does not vary, but if you try to increase the sensitivity by amplifying smaller charges(ie less light) you will increase the proportion of noise. Noise in ccd sensors is very dependant on temperature. Cooling your sensor will dramatically lower noise. This is why night time shots in the dead of winter will have less noise than on a hot summer night (but your batteries work better when warmer). In astronomical photography it is not uncommon to use active cooling of the ccd chip. bye for now Keith Cooper Northlight Images http://northlight-images.co.uk Photography - Digital Imaging - Apple Mac Consultancy Tel +44 (0)116 291 9092 Mobile +44 (0)780 162 9397 =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
