Optical measurement system with filter unit for extracting electromagnetic radiation

The system has a receiving unit whose rotatable interference filter (51) extracts electromagnetic radiation in defined wavelength range. A changing unit changes optical thickness such that extractable wavelength range is varied. The thickness is defined by refractive index of a cavity enclosed by semi-reflecting mirror elements of the filter and distance between the elements. The changing unit comprises actuator to change positions of the elements and/or refractive index adjusting element to change the refractive index. The thickness is sequentially changed during operation. An independent claim is also included for a measuring method for determining coordinates of points for distance measuring, using a geodetic surveying device, a coordinate measuring machine or a scanning device.