When you focus your lens on a subject, anything at that same distance from your lens will also be in focus. Things that are closer to or further from the camera lens will gradually - or quickly – get fuzzy. Your camera's aperture controls the size of this in-focus zone. The image above of the newspaper text is an excellent example of this.  This is called "depth of field", and the smaller your camera's aperture, the larger that depth of field zone is.

Nah, it’s easy.  Your camera’s aperture is just the hole in your lens that allows light into the camera.  In most normal cameras, this hole opens and closes to let in more or less light.  You’ve probably seen references to those little numbers in photography that look like “f/4” or something.  Well, those numbers tell you how large the opening of your aperture is.

Each of these f-stops lets in twice the amount of light as the next. I know that it seems a little weird that the smaller number lets in more light than the larger number, but there's a reason.

If you’re satisfied that I’m not lying to you and you didn’t like math in high school, and certainly don’t want to bring math into your hobby, you have a free pass to skip the next two paragraphs. BUT, if you are one of those people who just needs to know the reason, read on.

The “f-number” is a ratio. When you buy a lens for your camera (assuming its not a zoom lens), it will have a number on it, something like ‘200mm’. That number is the distance from the film in the camera to the lens, when the camera is focused at infinity. It's called your lens' focal length. (As with anything, of course there are exceptions - BUT - I'm doing my best to keep on track and just talk about aperture, so let's skip all of the crazy lens technicalities.)  The f-number is the ratio of that focal length divided by the diameter of the aperture (the width of the opening).

To put all of that gobbledygook simply, when the aperture of a 200mm lens (focal length) is 50 mm (aperture opening) wide, your f-stop will be f/4, because the ratio of 200/50 equals four. If you "stop down" your aperture to half that size - 25 mm wide - your f-stop will be f/8. (200 divided by 25.) So the "f-number" gets larger as you let in less light.

Whew!  Okay. Enough technical stuff. What does all of that have to do with this “depth of field” thing?  As I said in the beginning, when your camera’s aperture is open wide, you’ll get a very shallow dept of field, like the newspaper picture.  When it is closed down (also referred to as “stopped down”), you’ll get a very deep depth of field.

Look at the following photos, for example.  I took some sparkly party hats printed with a bright, crazy pattern of butterflies and flowers, and cut a butterfly out of one of them.  I held the cutout butterfly close to my camera lens and put one of the party hats about a foot away as a background.  Then I took two pictures – one using a wide-open aperture and one using a small aperture.  You can clearly see how in the first image, the shallow depth of field throws the background out of focus and makes the subject stand out, whereas in the second photo with deep depth of field, the patterns all blend together and you can barely distinguish the subject from the background.  Blurring out the background using depth of field also got rid of that distracting wrinkle in the background.

This technique can come in particularly handy in portraiture. Tightly focus on the subject's face and open up your aperture to blur whatever is in the background. You'll have a portrait that jumps out at you – whammo!  Notice in the following photo, the background is beautiful, but virtually the same color as the subject’s face and hair.  Using a shallow depth of field really makes the boy stand out.

You can also use depth of field to create a sense of distance.  For example, in this photo, the billiard ball that is in focus seems to really stand out far away from the other due to the depth of field used by the photographer.  In actuality, they may only be a few inches apart, but depth of field here really makes the ball in the foreground stand out, adding impact to the composition.

Lastly, you can use depth of field to make one object stand out from a large group of similar objects. The following image would be much less interesting without the varied depth of field. Having that single lock in focus and the vibrant red throughout really makes the focal point of the image “pop”. You will often see this technique used successfully with rows of similar items.

And then, of course, there are the times you want to use deep depth of field – so that just about everything in the picture is in focus. This is commonly used in landscape and architectural photography, and a small aperture is the way to go. Check out the crisp foreground and the clear lines of the trees on the horizon. Beautiful! You really feel like you’re standing there, taking in the view, while being almost able to “touch” the flowers that are closer to you.

There are exceptions to these rules for changing depth of field in the composition of your photograph. But the key is to never quit being creative and having fun. Now go out and mess around with your depth of field and see what you can come up with!

Photographer Credits:
"business section" by halbergman
"Portrait little boy" by joeybrooke80
"Pool Balls - Gritty 1" by ntmw
"Locker row 2" by pablohart
"flowery landscape" by puchan