Depth of field is the amount of focusing in an image; it usually is defined by background and foreground. So if either of them is out of focus, it has a SHALLOW DEPTH OF FIELD. If both factors; the entire image; is in focus, then it is known as DEEP DEPTH OF FIELD.
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(Source: flickr) |
Depth of field and aperture are closely related – beside the controls of brightness. Aperture is the hole inside the lens in which opens up to let light in, this controls how much light is going through the lens. This is measured in something called F-STOPS; they range from around f/2.8 to f/22. The term STOPPING DOWN is basically halving/descending in the numerical scale of these stops; STOPPING DOWN doubles/ascends the number.
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(source: Google Images) |
There is often confusion in recognizing the relation between the size of the hole and the f-number itself, usually; the smaller number would feel right to match the smaller hole. In fact, this does not apply, the larger the number, the smaller the hole and the smaller the number, the bigger the hole.
The way this works is through the light rays; this is called the CIRCLE OF CONFUSION. This is the circle of light formed by the lens through the aperture hole, the less spread out the light rays, the less areas of focus there is, hence the smaller hole having less focused features in an image.
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(Source: Google Images) |
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(Source: Google Images) |
The differences between lenses and depth of field are quite contrasting. Taking an image far back with a wide angle lens gets the whole scene into focus, whereas the same distance with a zoom/telephoto lens, the tighter frame has a shallower depth of field. The reasons that these lenses do this, is because a zoom lens is thinner, it’s shaped in a concave way, therefore the light rays passing through in a thin path, a wide angle lens is much thicker and it’s more curved to spread the light ray path. With a macro lens, they have very shallow depth of field; this is because they are built to only focus a few inches out from the lens itself. Whereas, with landscape photography, focusing on the infinite gives a much deeper depth of field. (images)
To summarize these findings and to define facts that I can use within this assignment, here are the ways to achieve the desired depth of field.
Shallow depth of field requires: A large aperture, a closer distance to the subject and zooming in for a longer focal length.
Deep depth of field requires: A small aperture, a larger distance from the subject and zooming out for a shorter focal length.
