Alpha Photography Blog

Depth of field is one of those techniques which is fundamental to good photography.  Here I’ll go through a demonstration on how to achieve two outcomes using aperture to achieve the desired depth of field, and a practical example to explain this concept.

Depth of field is directly related to the aperture level you set your camera at.  This isn’t the most intuitive of concepts, so I’ll explain in a few different ways.

Firstly, aperture is the size of the hole through which light passes.  Say you’re taking a photo of a person with a view in the background, and you want the entire frame to be sharp, you want there to be less specific depth, with the entire image to be in focus.  Here you want a smaller hole for light to pass through, so that the depth is longer. 

Where the hole is larger, the image depth is assessed more, and you can select the foreground to be in focus, while the background is out of focus.

On one end of the depth of field spectrum is a shorter depth of field, while at the other end is a longer depth of field.

Aperture is measured in terms of an ‘f stop’ - for example, a standard aperture is f8.0.

Here is how it works - unfortunately, there’s no other way to remember this than to rote learn it, and apply it in practice:

• Shorter depth of field = smaller f stop
• Smaller f stop = larger aperture (i.e. the size of the hole)

• Longer depth of field = larger f stop
• Larger f stop = smaller aperture (i.e. the size of the hole)

Here is a demonstration of a shorter depth of field, and longer depth of field:

Shorter depth of field

These two sample images were taken with an aperture of f5.6. The corresponding shutter speed was set so the photo was correctly exposed.

Notice how the focal point of each image is in focus, while the background is blurred.  This is a common technique for portait photography, and really emphasizes the subject, while adding mood to the background.

Referring to the above, the smaller the f stop, the larger the aperture (i.e. the hole), and the more depth that is defined.  In these photos there is a clear distinction between foreground and background, adding more depth and dimension to the image.

In the case of the bird, I wanted to emphasize the foreground - particularly as the bird was looking right at me - and blur out the background.  If the background was also in focus, it wouldn’t nearly have the same effect, as the bird would just be part of his surroundings, rather than being the main focus of the image.

Where you want the entire image to be in focus, then you will be wanting a longer depth of field…

Longer Depth of Field

Here is an example of the other end of the depth of field spectrum.  Compare it to the flower photo above.  In that photo I wanted to set one poppy apart, somewhat blurring the background  Whereas, in this image I wanted the entire field to be the subject of the image.  There is a little less depth in this image, as the focus reaches out farther into the distance.

In this case I used an aperture of around f22.

It all depends on the result you want to achieve in your image.  It’s not the easiest concept to grasp, so hopefully this has helped clarify the concept of depth of field.

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