For our measurements, we use a simple but very precise measuring method, namely that of the so-called “shadowgraph image technique”. The spray is positioned between a light source and a camera. The very bright light source creates a backlight that is picked up by the camera. If a droplet falls between the light source and the camera, it creates a shadow in the image, as shown in the animation on the left. Using a reference scale of known length, the size of each droplet can then be determined. In the reference image on the left, the inner circle corresponds to a diameter of 250 µm.  Since the droplets are mostly very small, we use a far-field microscope and can resolve droplet sizes down to 5µm. Due to the measurement method, many out-of-focus droplets appear in the raw data image. These droplets are outside the focal plane and can be larger or smaller than they are in reality and are therefore discarded for the distribution determination. With our automatic traversing device (traverse) we can automatically measure at different positions of the spray to also determine a position-dependent droplet size distribution. The recorded images are then evaluated by our in-house software (see below). The advantage of this measurement method is that we can get a good overview of spray properties. Most laser-based methods work mostly on a black box principle and thus provide little insight, but are blazingly fast.