What is Depth of field

What is Depth of Field

When you first pick up a camera and everything is still quite new, it is a lot to take in. You hear the word “aperture” and the words “shutter speed” perhaps the words “Depth of Field” not realizing that you just heard about the things that will dominate your photography forever. Not just at the beginning of your photography education but FOREVER.

So what is Depth of Field? It’s the area within any photograph that is reasonably sharp or acceptably sharp. If you look at an area of a photograph and you can see the detail due to the sharpness of the image then that person or object would be considered to be within the area we call depth of field. Which is essentially the area within a photograph that is acceptably sharp. Anything in front or beyond that point that is not acceptably sharp is considered to be outside the depth of field. To make it even more confusing DOF changes in almost every single shot!

What things affect Depth of Field.

  • Aperture.
  • Focal length?
  • Distance to subject.

Lets start with aperture. The aperture is effectively the hole inside the lens that lets light into the camera to form an image. If the aperture is small the DOF will be greater and if the aperture is large the depth of field will be smaller. So the same shot taken at F22 (Small aperture) will have more depth of field than a shot taken at F5.6 (Large aperture) Notice the larger number represents a smaller hole. This is just another thing that helps to confuse people. Don’t worry this all becomes second nature eventually. You will be thinking about this every time you pick up your camera.

Now then let’s talk about focal length. How does that affect depth of field? Take an image of a woman from 20 feet away with a 50mm lens and let’s say you can get her whole body in the shot. Now you take the same shot with a 200mm lens from the same spot, you would likely only be able to get her head in the shot. Now here is the strange part, the shot taken with the 50mm lens will appear to have more depth of field, because it has a wider angle of view. The 200mm lens has greater magnification. Now if you walked backwards far enough so that while you were using the same 200mm lens that you could fit the whole woman in the shot, same angle of view. They would both have the same DOF. The only thing that has changed is the distance to the subject.

Distance to subject. How does that affect depth of field? Thankfully this part is easy. With any given lens, at any given aperture, the closer you are to the subject the less DOF you will have. That is why small apertures F16 and above are typically used in macro photography.

There is also a common misconception that depth of field extends twice as far beyond a subject than it does in front of the subject. This is true with wider lenses but is not always the case as you increase the focal length of a lens it becomes less true and is much more likely to be the same in front of the subject as it is beyond the subject with longer lenses.

So how do you control Depth of field?

If you want to control DOF you can adjust the aperture to give less or greater depth of field. You can also move closer or further away from the subject and use wide or narrow angle of view.

This is a skill that you will come to master and use in all types of photography. In landscapes you will typically want greater DOF, while in portraits you will likely want less depth of field.

Please leave a comment or ask a question at the bottom of the page.

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