One of the most important things to understand if you want to take your photography to the next level, depth of field. But what is it? Professional photographs always have one thing appearing sharp (the focal point of your photo) and other elements of a photo appear blurry. That is depth of field, the portion of a photograph that appears sharp.
Depth of field (wikipedia)
the depth of field (DOF) is the portion of a scene that appears acceptably sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.
Depth of field can be used to emphasize an element of your photograph as seen in the following example.
It is clear that the bell is the subject of this photograph, and not the fence in the background. Although the fence adds an interesting pattern, if it appeared to be as sharp as the bell it would detract from the overall composition.Instead a very small depth of field was used to emphasize the bell. A very large depth of field would have produced sharpness across the entire photo.
How is depth of field controlled?
Read the full wikipedia article to really understand how focal lengths and lenses affect depth of field, but in simple terms you can use one of your cameras settings to control depth of field… aperture. The size of your lens aperture directly affects depth of field. By simply adjusting the size of the aperture (f number) on your camera different depths of fields can be achieved.
A large aperture (small f number) produces…
small depth of field (subject sharp, more foreground/background blur)A small aperture (large f number) produces…
large depth of field (sharpness across the entire composition, less to no blur)
An example to illustrate
The following examples were shot in manual mode, with a tripod at ISO 100 using an SMC Pentax-A 50mm lens focused on the head of the giraffe. (approx. $20 kit lens from an old Pentax 35mm film camera)
f2 1/45s
The head of the giraffe was focused on, and since the aperture was at f/2, only the giraffe’s head is sharp.
f9.5 half second exposure
The same shot and focus point, but with a smaller aperture. The result is that the giraffe’s body is mostly sharp. The background elements are still a little blurry, but are now identifiable.
f22 three second exposure
Now with the aperture even smaller the entire composition is sharp, but note that I had to use a 3 second exposure.
Depth of field, experiment with it!
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