One of the most important principles for capturing an image with your cameras is being able to understand and adjust your cameras aperture.
Aperture, in it's most basic explanation, dictates the size of the hole in your lens, controlling the amount of light that can pass through it and reach the sensor. Your aperture is the diameter of this opening, which contracts or expands depending on how you set it.
Apertures on most modern DSLR or mirrorless camera lenses tend to range from f3.5 to f22. Other can go expand beyond that and go as low as 1.4 all the way up to f44 and further still.
At your cameras lowest aperture anything from f4, f2.8, f1.8, f1.4 you are opening up the lens wider and allowing the most light to enter. The higher you take your aperture, f16, f18, f22 and above, the smaller the aperture diameter becomes and the least amount of light is able to get through your lens and onto the sensor to expose your image.
There are benefits to working at both higher and lower apertures. By understanding what the end result at each end of the scale is, you'll be better able to make the creative decisions necessary to capture the image just as you intended.
The diagram below allows you to better visualize what is happening when you make these adjustments.
When we shoot images at the lowest aperture available we're allowing the most light possible to enter the lens. This allows you to shoot in lower lighting conditions and maintain a quicker handheld shutter speed. You can also work with a lower ISO that will keep any noise in your image to a minimum.
You'll start to notice that beyond your point of focus the background will actually drop out of focus. This is used mostly in an artistic way that allows you to cleanly separate your subject from the background, and is particularly useful in scenarios where the background you're working with is cluttered or distracting. It's most commonly referred to as a shallow depth of field.
Shooting at a higher aperture (f16, f18, f22 and beyond) we're restricting the amount of light that can enter the lens. There are times where you'll want to shoot at a higher aperture in order to achieve maximum depth of field where as much of the foreground and background is in focus along with your subject. The complete opposite effect of working at a lower aperture as mentioned above.
Take a few photos at your lowest and highest apertures and compare the differences. You'll be amazed at the differences. Below are a few examples we've found that showcase the differences really well.