Fluid stream imaging apparatus

A flow cytometer comprising:

• a. a fluid delivery system having a nozzle for producing a fluid stream, the fluid delivery system having an oscillator for perturbing the fluid stream into droplet at a break off point downstream of the nozzle;
• b. an excitation energy source for interrogating the fluid stream at an inspection zone;
• c. a detector for detecting electromagnetic radiation from particles at the inspection zone and for determining particle characteristics;
• d. a controller for charging the fluid stream based on the detected particle characteristics;
• e. an optical system for producing a image of the fluid stream, the image of the fluid stream including at least the break off point, wherein the optical system takes multiple images per droplet;
• f. a sensing element for sensing a plurality of images of the fluid stream;
• and
• g. a processor for processing the detected image of the fluid stream, wherein the processor is responsive to images of the fluid stream to determine the time at which a droplet breaks off the fluid stream.