Am I the only person who is too thick, or too ignorant, to understand Bob Newman's article? I thought that when we changed the iso setting of a digital camera then we were changing the analogue gain prior to A/D conversion so that the range of charge on the sensor is matched to the range of pd allowed by the 14 bit converters. It seems that I was wrong but cannot see what really happens. I feel that a further article, starting with the basics and then explaining this week's article might be helpful. If this doesn't merit another article on the subject then perhaps Profbob might be puersuaded to write something for the AP web site.