  Optical distortions can significantly deteriorate the measurement accuracy in
imaging systems. Such distortions can occur at fluctuating phase boundaries as
well as multiple-phase flows and result from the accompanied refractive index
changes. Due to multiple reflexes arising from a fluid flow setup, the usage of
a wave front sensor (WFS) can be hindered. In this work we outline a wave front
sensor-less approach which includes iterative aberration correction with a fast
deformable mirror (DM). A combination of sharpness metric (SM) image evaluation
and iterative optimization is demonstrated. The SM was measured for each image
while adjusting seven Zernike modes (after Noll index enumeration) in their
amplitude. The SM is used as an indicator for wave front aberrations without
using a wave front sensor to correct wave front distortions that are generated
by the DM. The proposed method allows for the reduction of systematic
measurement uncertainties in fluid flow measurement techniques as particle
image velocimetry (PIV). Five different sharpness metrics are demonstrated for
reliable sharpness maximization with a deformable mirror of 69 elements. A
systematic linear search (LS) algorithm was applied in order to find the
optimal mirror shape. The reduction of measurement uncertainty for PIV
measurements is shown. The iterative approach offers a way to reduce static or
slowly changing wave front distortions in a fluid flow setup where a WFS is not
applicable.
