Out of Focus? Precision Aspects of Micro-PIV

In a common implementation of microscopic particle-image velocimetry (μPIV) the studied flow is volume illuminated [1,2]. An optical section of this flow is taken by imaging the tracer particles added to the flow. The thickness of the optical section depends on the depth of field of the imaging system. The optical section determines the thickness of the measurement volume, and thus the axial resolution of the μPIV measurement.