Chapter 4. Aperture
The aperture is the opening in the lens that light passes through to reach the sensor. By controlling the size of the opening, you can control how much light reaches the sensor. The bigger the opening, the more light is able to pass through. The size of the opening is notated using f-stops. While changing the aperture allows you to change the amount allowed light to travel through the lens, it also changes the depth of field. This gives you control over what is in acceptable focus in your image. Controlling the aperture controls the depth of field and mastering how that relationship works is important in getting the results you want. Because the aperture is in the lens and not in the camera, you need understand prime lenses and variable aperture lenses and the effects that each can have on your photography.
This chain link fence was shot on the streets in New York. I like this photograph because the fence is in sharp focus, but the walls behind them are blurred. Controlling the aperture created this effect. Taken at 1/400 second, f/2.8, and ISO 200.
Controlling the Aperture
With digital cameras, the aperture controls are part of the camera, usually a dial on the front or back that changes the physical size of the opening in the lens, but it usually doesn't physically change the opening until you press the Shutter release button. This allows the most light to pass ...