A method for determining a set-point voltage (Vx) for a piezoelectric actuator system to achieve a desired optical response of the piezoelectric actuator system, wherein the piezoelectric actuator system comprises an optical member (130, 120) with an adjustable optical response and a piezoelectric actuator, the method comprises - providing a mathematical model, OP(V,T,n), describing a relationship between a voltage applied to the piezoelectric actuator, a temperature and a transition time count value (n) as variables and the optical response, where the mathematical model comprises a curve fitting polynomial, and where the transition time count value (n) relates to at least one transition time value (x) of the piezoelectric actuator for changing from a first state to a second state, - calibrating the mathematical model by - determining a calibration transition time count value (nCAL) based on determining the at least one transition time value (x) between the first and second states (X1, X2) of the piezoelectric actuator, - obtaining a calibration temperature (TCAL) of the piezoelectric actuator, - determining one or more calibration parameters (oCAL, bCAL) of the mathematical model, OP(V,T,n), based on one or more calibration voltages (V1, V2), and one or more optical responses (OP1, OP2) associated with the one or more calibration voltages (V1, V2) applied to the piezoelectric actuator, - after a period of time or use of the piezoelectric actuator, updating the mathematical model, OP(V,T,n), by - obtaining the temperature of the piezoelectric actuator, - determining the transition time count value (n) based on determining the at least one actual transition time value (x) between the first and second states of the piezo electric actuator, - determining the set-point voltage (Vx) based on the updated mathematical model, OP(V,T,n), and applying the set-point voltage (Vx) to the piezoelectric actuator. - providing a mathematical model, OP(V,T,n), describing a relationship between a voltage applied to the piezoelectric actuator, a temperature and a transition time count value (n) as variables and the optical response, where the mathematical model comprises a curve fitting polynomial, and where the transition time count value (n) relates to at least one transition time value (x) of the piezoelectric actuator for changing from a first state to a second state, - calibrating the mathematical model by - determining a calibration transition time count value (nCAL) based on determining the at least one transition time value (x) between the first and second states (X1, X2) of the piezoelectric actuator, - obtaining a calibration temperature (TCAL) of the piezoelectric actuator, - determining one or more calibration parameters (oCAL, bCAL) of the mathematical model, OP(V,T,n), based on one or more calibration voltages (V1, V2), and one or more optical responses (OP1, OP2) associated with the one or more calibration voltages (V1, V2) applied to the piezoelectric actuator, - determining a calibration transition time count value (nCAL) based on determining the at least one transition time value (x) between the first and second states (X1, X2) of the piezoelectric actuator, - obtaining a calibration temperature (TCAL) of the piezoelectric actuator, - determining one or more calibration parameters (oCAL, bCAL) of the mathematical model, OP(V,T,n), based on one or more calibration voltages (V1, V2), and one or more optical responses (OP1, OP2) associated with the one or more calibration voltages (V1, V2) applied to the piezoelectric actuator, - after a period of time or use of the piezoelectric actuator, updating the mathematical model, OP(V,T,n), by - obtaining the temperature of the piezoelectric actuator, - determining the transition time count value (n) based on determining the at least one actual transition time value (x) between the first and second states of the piezo electric actuator, - determining the set-point voltage (Vx) based on the updated mathematical model, OP(V,T,n), and applying the set-point voltage (Vx) to the piezoelectric actuator. - obtaining the temperature of the piezoelectric actuator, - determining the transition time count value (n) based on determining the at least one actual transition time value (x) between the first and second states of the piezo electric actuator, - determining the set-point voltage (Vx) based on the updated mathematical model, OP(V,T,n), and applying the set-point voltage (Vx) to the piezoelectric actuator.