A Focused Shadowgraph Imaging System (FoSI) camera with a new image analysis algorithm has been developed to study particles from the surface to the deep sea. FoSI is uniquely able to capture low-density and small particles that are underestimated using conventional optical systems and uses an image algorithm incorporating an improved edge detector to reconstruct particle contours. Using data from deployments in the Sargasso Sea, we found that particle numbers throughout the water column better correlate with beam attenuation than total particle volume. This results from the fact that larger particles are rare events which contribute to total particle volume but are undetected by the transmissometer. Chlorophyll a was poorly correlated with both particle number and volume. Assuming that optical density is correlated with the physical density of particles, the observed patterns in the relative abundance of fainter particles may provide new insights into the average sinking velocities of particles throughout the water column.