Fill Flash Outside Posted on March 14, 2022 by emmanuelg70 Fill Flash is a photography technique in which the camera flash is deployed to illuminate the darker areas of an image, especially the subject. When the subject is underexposed due to the deficit of sunlight and other lights or sometimes due to the backlight, fill flash is supplemented to correctly expose the subject. For many photographers, using fill flash is a daunting task as they apprehend overexposure of a photo. But with the appropriate use of a fill flash, you can nail your photography.