Flash Techniques: Fill Flash I’m surprised at the number of advanced photographers who remain mystified by fill flash.  This powerful technique is simply the blending of two light sources during one exposure.  The primary light source is natural light and the secondary light source is your flash.  During full flash the camera is arbitrarily set at the highest synch speed, but with fill flash, simply shoot in aperture priority and let the flash do the rest. Aperture priority [...]