Response to asa

You set the ASA, now called the ISO, at what the manufacturer puts on the box. Then you test a bit to see if your results are good at that stated speed. If not, you change it to what works for you and then call it your Exposure Index, YOUR tested speed for best results. It is just like getting a new car and finding out where the gas tank really goes dry. Before the mark, at the mark or well after the mark when you get past Empty to 'I'm not fooling' and the car stops.

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