OPTICAL ELEMENT CONTROL
There is provided an optical system comprising an optical element (10) responsive to an applied signal to vary an optical property of the optical element (10), the variation of the optical property with the applied signal exhibiting hysteresis in a first range of values of the signal, and no hysteresis in at least one second range of values of the signal. The optical system further comprises a memory storing data representative of a variation of the optical property with either increasing values of the signal or decreasing values of the signal, and a controller configured to control the optical property of the optical element (10) by generating a control signal based on the stored data and applying the generated control signal to the optical element. In a case where the memory stores data representative of the variation of the optical property with increasing values of the signal, the controller is configured to use the stored data to change the value of the optical property from an initial value corresponding to a first value of the signal, to a subsequent value corresponding to a second value of the signal that is smaller than the first value of the signal, by setting the value of the control signal to a third value that is within the second range of values, and subsequently increasing the value of the control signal from the third value to the second value. Alternatively, in a case where the memory stores data representative of the variation of the optical property with decreasing values of the signal, the controller is configured to use the stored data to change the value of the optical property from an initial value corresponding to a first value of the signal, to a subsequent value corresponding to a second value of the signal that is greater than the first value of the signal, by setting the value of the control signal to a third value that is within the second range of values, and subsequently decreasing the value of the control signal from the third value to the second value.