Depth of Field

One of the most complicated things to understand when it comes to photography is Depth of Field.  My goal with this blog is to try to explain things as simple as possible for those trying to learn photography.  When I started out it seemed like everything I read was written for people who already had experience and training in photography.  Having said that, this post is not for an experienced photographer.

When you visit most sites looking for answers about depth of field (DOF) you find complicated math formulas and diagrams about how light is reflected into the lens along with terms like "circle of confusion".  Its confusing.  So lets try to simplify this.

Depth of field is how much of you image is in focus, behind or in front of your subject.  Those nice blurred backgrounds you often see in professional photographs is what we all strive for.  It helps to isolate your subject and make them stand out.

In the pictures below I am able to tell two different stories with the same subject.  In the first picture I focused on Samantha's finger.  The second photo I focused on her face.  Because I shot this photograph from about 10 feet with an aperture setting of f/2.8 I was able to make whatever I wanted in focus while the rest was blurred.

I have to give credit where credit is due.  I learned this example from Jeff Cable.  Jeff is an Olympic photographer and a marking director for Lexar.  He is an amazing photographer and gives some outstanding lessons you can find on YouTube.  You can also visit his website JeffCable.com where he talks about how he takes pictures.

So lets try to simplify this.  If you were to press your nose up against a window, and I focused on the tip of your nose, everything along the window would be in focus.  Depending on my camera settings, everything in front of or behind of the window will be out of focus.  Depending on how far away from the window you are will determine how out of focus it will be everything that is not on the window plane will be out of focus.

Now that is an extremely simplified answer.  Perhaps over simplified.  Because your camera settings will determine what if anything is out of focus.

So what camera settings am I referring to.  The first is your aperture, commonly referred to as f stop.  The lower the f stop number, the more ability you have to control your depth of field.

Now to really make this confusing, your focal length and distance from the focus will also affect this.

But for simplicity we will try to just focus on the F stop setting for now.

In the pictures above with Samantha pointing her finger I set my aperture (f Stop) to F2.8.  This gives me a very shallow depth of field.  The further an item is in front of behind the focus point, the more it will be out of focus.

In the picture below my F Stop was set to about F/11 or F/12.  I wanted both the pitcher and batter in focus.

Depending on your camera and lens, you may not be able to set your F stop to an F/2.8.  Many lenses that come with a camera have what is known as a variable aperture.  Meaning as you zoom, the f stop changes.  Often you see lenses that are a 3.5 - 5.6 or even higher numbers.

You have to buy better lenses to get the lower numbers.  A very inexpensive lens for Canon shooters is the 50mm f/1.8 lens.  You can buy this lens at Best Buy for around $120 or even less online.

This lens, especially set at f/1.8 gives you such a narrow field of focus that you can have an extremely shallow depth of field.  So much so that you can have the nose in focus, and they eyes beginning to be out of focus.

In the picture below I focused on the far eye of my son.  Notice how the eye closest to the camera is slightly out of focus.

In the picture below you can see that my youngest son who is sitting in the front, is slightly out of focus.  That is because I used a setting of 2.8 and focused on his brother in the blue hat.

Everything behind them is beginning to get out of focus, but not by much.

The further behind your subject, the more it will effect the bokeh, or the blur of the background.  

You can find Depth of Field calculators online where you can input your focal length, distance from subject and aperture setting and the calculator will tell you how much your depth of field will be both in front of and behind your subject.

But to be honest, I learned this simply by shooting thousands of images at various distances and focal lengths as well as aperture settings until I felt comfortable gauging by site what the image would look like.

Like anything, practice is the best way to learn anything.  Photography is no different.