You should use flash when shooting macro in these 5 different situations. Dim light. Use a flash when you're shooting in a dimly lit environment and you can't use a tripod and slow shutter speed to get a proper exposure. Freeze motion. When you can't use a super fast shutter speed to stop all blur from a moving subject, the super short duration of a flash will freeze your subject's movement. Depth of field. When you can't stop down your macro lens to a tiny aperture to achieve deep depth of field in the existing light, the brightness of a flash will allow you to shoot at small lens openings and get more or all of your subject in focus. Darken background. Light from a small flash unit falls of quickly in brightness. Your subject will receive much more light than a background that is further away from the subject. The background will be darker in your photo and this will make your subject stand out more. Fill light. Setting your flash to a reduced power setting will make it good for filling in the dark shadows of your subject, but have much less effect on the highlight areas of your subject.