By this app, you can use your phone as incident light meter,and you can take a picture of the correct exposure. This app can measure 'F number' , 'Shutter speed' or 'ISO sensitivity'. Set these measurement values at your camera. Change your camera to manual mode when setting the values. Digital cameras have a built-in exposure meter. However, since the built-in exposure meter is reflective, it may not be able to accurately measure exposure because it is affected by the color or gloss of the su