Nice reminder of the tradition diagram. But I don't accept the professor Newman's agument that it is showing that 'ISO is defined in terms of exposure', rather that Exposure is influence by the three variables shutter speed, appature and ISO. So be it ISO or the older film term ASA, it is the light sensitivity of the recording medium, be that film or ccd sensor etc. that we are interested in. With film the chemical emulsions used altered the sensitivity and gave variations in texture, colour or shade (panatomic/panachromatic) rendition of reflected light in an image. ISO for me in digital photography is the adjustment of the camera's sensor circuits. The circuits have been tuned to mimic or match traditional film light sensitivity values, I think because that is what users were used to. What this does not do is match the differing film emulsion characteristics. I feel a comparison of the charateristics of film and digital to that of valves and transistors, one is organic and almost warming the other clinical brash and potentially quite harsh. Guitarists often all these years on since the invention of the transistor still often choose valve amplification. There is room for more film and clearly as the star letter of the week in this issue showed, people are coming back to it.