After a recent conversation, I really got into thinking about Depth of Field, and thought I would post something about it. My girlfriend was taking some pictures and we got to talking about depth of field. Well, it seems that she had been taking pictures at f/1.8, from about 3′, which equals about 1.25″ depth of field with her lens. This made me look around for information about depth of field. I took 4 pictures with my 50mm Canon macro lens. I took the pictures at 2.5, 5.6, 9, and 13 aperture. This gives a visual representation for my example. This is paired with an application at dofmaster.com. These pictures are taken on a Canon XSi, about 7 inches away.

This picture is at f/2.5 – The depth of field is about .03″. The applications shows .02″ in front and behind my focal plane. There is not a lot of depth of field here.
Poker Chips - f/2.5

This picture is at f/5.6. The Depth of field is a total of .08″. The applications shows .04″ in front and behind the focal plane.
Poker Chips - f/5.6

This picture is at f/9. The depth of field on this one is about .12″. The applications shows about .06″ in front of and behind the focal plane.
Poker Chips - f/9

This picture is at f/13. The depth of field on this one is about .18″. The applications shows about .09″ in front of and behind the focal plane.
Poker Chips - f/13

What I find very interesting, is what happens as you move to longer distances, the balance of the depth of field goes from nearly even, to more and more depth of field behind the subject. For example, with this combination, at 10′, the depth of field is balanced at 35% in front of the plane of sharp focus and 65% behind the plane of sharp focus. At double that distance, the depth of field extends 19% in front of the subject, to 81% behind the subject.

Before looking at the calculator, I had been wondering what the actual depth of field “spread” was. Finding that it is 100% dependent on subject distance should have been obvious to me, and I understood how it worked, without thinking about it. By learning the technical specifications of how it works, actually adds it to my photography toolbox, to use later. For the most part, I do not think about depth of field, beyond the fact that a smaller aperture, gives me a greater depth of field. If you need to get technical, many modern smart phones (like the G1, iPhone, and Windows Mobile based devices) have DoF calculators, and/or you may be able to use the mobile web to access the Online Depth of Field calculator I have been using.

Adding tools to your personal toolbox helps you to become a better photographer. I hope this quick primer on DoF helps you, on your way in this wonderful hobby, called Photography.

I want to share one more picture. This is one of my all-time favorite pictures I have taken. It also happens to be one of the earliest pictures I took with my SLR. The Depth of Field really stands out, with the gosling’s head in focus, and you can see the grass below it, how shallow the actual Depth of Field was. But, since I was taking the picture at it’s profile, I didn’t need a lot of depth of field. I was shooting as open as possible, on that lens, since the goslings were moving so fast.
Gosling eating grass
Thanks to Baz from dpreview for help clarifying the difference between plane of sharp focus and focal plane. (The focal plane actually being the point where the surface of the sensor is)
Thanks to WilbaW from dpreview for a link to a technical article about Depth of Field or Field of Focus. The link can be found here: http://www.hobbymaker.narod.ru/English/Articles/sharpness_eng.htm. It is pretty techincal, and I plan on figuring it out, in the near future.