An imaging system is installed on the retractor. A light source, which operates  both  as a  flashlight or a continuous light is located at the back side of the retractor. The power supply  of  the  imaging system is located inside the handle.  A camera is located at the opposite  side of the light source. In our current design, the spray nozzle is located in between the light source and the camera. Therefore, the spray or aerosol passes in between the light source  and the camera.  This  allows for proper characterization of the aerosol and  determination  of the  aerosol  droplet  number  density and droplet size.  These  characteristics  are  then  used  to  calculate  the  amount of  mass  that  is applied to any location.