  We discuss the design and operation of a confocal rheometer, formed by
integrating an Anton Paar MCR301 stress-controlled rheometer with a Leica SP5
laser scanning confocal microscope. Combining two commercial instruments
results in a system which is straightforward to assemble that preserves the
performance of each component with virtually no impact on the precision of
either device. The instruments are configured so that the microscope can
acquire time-resolved, three-dimensional volumes of a sample whose bulk
viscoelastic properties are being measured simultaneously. We describe several
aspects of the design and, to demonstrate the system's capabilities, present
the results of a few common measurements in the study of soft materials.
