This is a sample of 1 micron Silica. The particles are too small to resolve, however they clump together to form bigger particles that can be seen.  The out of focus areas are too close or too far from the lens to be in focus. The sample is placed on a black anodized aluminum plate. The illumination was by the red, green, and blue LEDs in the optical head.  This image is a composition from 3 monochrome images. The individual images are shown in thumbnail below. Clicking on a color name will take you to a full size view. The UV image shows thermal noise in the sensor. 

              Red ( Full Size View)                             Green ( Full Size View)                        Blue ( Full Size View)                            UV ( Full Size View)