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May 12, 2017

The aperture is the hole in your lens that allows light to reach the sensor. Just as the shutter speed changes the length of time light is reaching the sensor, the aperture regulates the amount  of light that is going through your lens.
Aperture is represented in something called f-stops and can follow a range of f1.4, f2.8, f4, f5.6, f8, f11, f16, f22, and beyond. Not all cameras/lenses will be able to set all of the stops I’ve listed but these are the most common. f1.4 represents the largest hole in the lens and will let in the most light, and conversely f22 is the smallest hole and therefore lets in the least amount of light.
Each change in f-stop represents a doubling or halving of the amount of light going through your lens, so changing from f5.6 to f4 will let in twice as much light, and conversely changing your f-stop from f5.6 to f8 will cut in half the amount of light reaching the sensor. You may recall that changing your shutter speed up or down will cut in half or double the amount of time that light is reaching the sensor, so pairing changes in shutter speed with changes of f-stop gives you ultimate control over your exposure.
By setting your shutter speed as was discussed in my previous posting, you can alter your aperture so that the amount of light reaching the sensor will give a proper exposure. In a really bright outdoor scene where there’s a lot of light your meter might want you to set f16 or f22 to cut down on the amount of light that reaches the sensor, or in a dimly lit interior you might need a wide aperture like f2.8 or f2 so that enough light reached the sensor to make a proper exposure.
But changing your f-stop not only has an affect on the amount of light reaching the sensor, it also has a great influence on something called the Depth of Field. The Depth of Field is the amount of your photo that is in focus, from the foreground to the background. A wide aperture like f2.8 or f4 will give you a shallow Depth of Field, so not very much of the image will be in sharp focus in front of or behind the point you focused on. On the other hand, a small aperture like f16 or f22 will give you a much greater Depth of Field, so much more of your photo will be in sharp focus both in front of and behind your point of focus.
Depth of Field is much greater on wide-angle lenses than it is on longer lenses, so using this knowledge you can compose more dramatic photos. Let’s say that you want a wonderful landscape shot, by using a wide-angle lens and an aperture that gives a greater Depth of Field like f16 or f22 you can have everything in the photo in sharp focus. But if you want to isolate something against a blurred background, use a longer lens and an aperture that gives a shallow Depth of Field like f2.8 or f4 to get a sharp subject against a blurry background.
1/20th of a second @ f22 gives a large Depth of Field with everything in focus from foreground to background

1/320th of a second @ f3.5 gives a shallow Depth of Field with the subject sharp but the background out of focus
Try it out for yourself!
Next up…more examples showing Depth of Field techniques.