An object focuser may include a substrate, a sample fluid passage supported by the substrate, a first inertial pump supported by the substrate to pump a sample fluid entraining an object through the sample fluid passage, a first sheath fluid passage, a second inertial pump supported by the substrate to pump a first sheath fluid through the first sheath fluid passage, a second sheath fluid passage and a second inertial pump supported by the substrate to pump a second sheath fluid through the second sheath fluid passage. The first sheath fluid passage and the second sheath fluid passage are connected to the sample fluid passage at a convergence on opposite sides of the sample fluid passage.