Particle characterisation instrument

A particle characteristic measuring method, the method comprising:

• placing a sample in a sample cell,
• illuminating the sample with a light beam from a light source to produce scattered light by interaction between the light beam and the sample,
• moving at least one optical filter comprising a first polarizing filter and a second polarizing filter into a scattered light detection path between the sample and a detector using a filter changer, the filter changer comprising an actuator that moves the at least one optical filter between:
• a first position in which the detection path does not pass through the optical filter;
• a second position in which the detection path passes through the first polarizing filter;
• and
• a third position in which the detection path passes through the second polarizing filter,
• filtering the scattered light along the detection path with the first optical filter comprising a first polarizing filter and a second polarizing filter;
• and
• detecting the scattered light that has passed through the first optical filter with the detector,
• wherein measurements taken through the first polarizing filter are combined with measurements taken through the second polarizing filter to determine a depolarized dynamic light scattering measurement.