Wide Aperture Used to Soften Background Making it Less Distracting
Every camera lens has a small opening inside called a diaphragm. The diaphragm can open up to various widths to allow more or less light into the camera. This opening is called the aperture.
Apertures are measured in f stops. The smaller the aperture, the larger the f stop number (don’t ask me why, I think scientists like to make things harder than they need to be.) So an aperture of f4 will be considerably wider and let in a lot more light than an aperture of f22.
Just like with the shutter speed, each classic f stop will halve or double the amount of light coming into your camera and hitting the sensor, depending on which way you turn the dial.
So f8 lets in double the light of f11 and f16 lets in half the light of f11. The numbers are worked on a mathematical formula relating to the volume of a circle so they don’t double in number, they’re approximately multiplied by 1.4. (You don’t need to remember this it just helps you to understand the jumps in f stop numbers.)
The following diagram lists all the classic f stops. Remember that digital cameras may include half or third stops on the dial like with shutter speeds, so it’s a good idea to learn the chief stops.
What are the effects of changing the aperture?
Apertures, like shutter speeds, have their unique influence on the captured image. These effects can also be used creatively. When you focus on a subject the point at which you focus will be the very sharpest point in your scene.
Depth of Field
Depth of field means the amount of distance both in front of and behind your subject that will also be in focus. The smaller the aperture (higher the f stop number) the greater the depth of field.
A larger aperture (lower f stop) will give you less depth of field. This means that there will be less in sharp focus both in front of and behind your subject.
Portrait photography uses larger apertures to highlight the subject and soften the background behind them.
Larry Lizard was kind enough to pose for his portrait
The secret for achieving greatest depth of field in landscape photography.
The depth of field in front of your subject is always twice as large as the depth of field behind your subject. (Between your camera and the subject)
The trick is to focus on a spot somewhere approximately 1/3 of the way into your scene. This will maximise sharpness and depth of field from front to back.