value in the middle of its range a single pixel output or the average of a set of pixel outputs can be used as target value see details below if an ersd with analogue output connected as shown in fig2 is used the v ref is adjusted to a suitable value preferably in the middle of the ersd response range 2 an initial step value sv u03b4t of the shutter speed is defined as the maximum value 1 of the shutter speed divided by two if the shutter speed has 10 bit resolution its maximum value will be 1023 and the initial sv will be 512 3 the initial output of the shutter speed is set equal to sv and a u03b4t time shutter speed value corresponding to sv is transferred to the shutter speed control device 4 the steps below will be repeated n u2212 1 times n is the number of binary digits of the shutter speed if the shutter speed has 10 bit resolution n will be equal to 10 5 the current u03b4t time shutter speed corresponding to the input shutter speed value is transferred to the shutter speed controller 20 and the current shutter speed value output is used as the v ref and the resulting output from the adc is measured by comparing the new sv value is subtracted from the current.