For example, if you take a photo outside in bright sunshine (like the one on the previous page), you might require a setting like this to obtain the correct exposure at ISO 100: 1/90 second at f16 That means that when you take the photo the shutter will open for just 1/90 second. That’s not much is it? You probably couldn’t even see it with the naked eye. The shorter the shutter speed, the less light that reaches the sensor. F16 is a relatively small aperture . The smaller the aperture, the less light that reaches the sensor. In bright light you will require a relatively small aperture (or a very fast shutter speed) to obtain the correct exposure. Now, imagine that you are taking a photo outside, later on in the day, at dusk (like the photo on the right). Learn more at http://mpommett79.hatenablog.com/entry/2016/12/25/063905 and http://spanishinperu.org/nantucket-wedding-photographer-2015/
The light levels are dramatically lower than earlier. In this case, to obtain a correct exposure at ISO 100, you might need settings like this: 1/90 second at f2.8 The difference is that the aperture is set to f2.8, not f16. It is letting 32 times as much light pass through the lens. This compensates for the lower ambient light levels. This makes sense. Remember, at ISO 100, the amount of light required to obtain the correct exposure is the same regardless of how bright the ambient light is. So that means when the ambient light gets lower, you need to open up the aperture to compensate. You could also compensate by selecting a slower shutter speed (or a combination of both). In both examples, the net result is the same. The amount of light that reaches the sensor is exactly the same. The only thing that has changed is the level of ambient light, and the settings of both aperture and shutter speed to accommodate that. I took this photo in the same location but at dusk. The required exposure at ISO 100 in this case was an aperture of f2.8 and a shutter speed of 1/90 second. The only difference is with the aperture. It had to open a lot wider to let the required amount of light through. There is a difference of five stops between the aperture settings of f2.8 and f16. The quantity of ambient light was 32 times as great during the day than in the evening. There are several things you can do in Program mode that you can’t do in Auto. This varies between manufacturers, so check your manual. There is normally a chart showing which controls you can alter in different modes: • Control the ISO setting. • Adjust white balance. • Select a Picture Control setting. • Use exposure compensation. • Choose a metering mode. Don’t worry if some of these terms are new to you. They will be explained later on the ebook. The key thing about Programmed Auto mode is that it gives you full control over the camera settings. Note: P mode is called Programmed Auto by Nikon, Program Auto by Sony, Program AE by Canon, Fujifilm and Sigma, Program shooting by Olympus and Hyper-program by Pentax. Learn more at http://pomm79.moonfruit.com/blog/4588864419/Portrait-Photography-Tips-and-Reflections/11031618