Almost like an exclamation mark, selective focus creates a visual jump in a composition.
In any image, a mix of blurred and sharpened areas allow viewers to explore primary and secondary parts of the image in a systematic way – almost like a trail of breadcrumbs.
The focal plane – the region of the image in focus – has a variable thickness which extends in front and behind of the point of maximum sharpness. Depth Of Field (DOF) is this area’s width.
DOF is dependent on a lens’ sensor size, focal length, diameter, aperture setting, and the distance between camera and subject.
The larger the sensor, the shallower the DOF and the more selective you can be – such as in a 35mm cinema camera or DSLR. A shallower DOF is the product of a lens with longer focal length.
Another way to achieve a shallow depth with an ultra-wide lens is to ensure the subject lies very close to the lens. However, focusing in this case may be difficult.
On the other end of the spectrum, small-sensor video cameras produce a very wide DOF. To prevent this, focal length should be increased to a maximum to bring the subject closer through zooming.
Near and far
When lens focal length, sensor size and subject distances are equal, DOF relies on the aperture of the lens.
When aperture is narrower with a larger f-stop value, the diameter of the lens gets smaller which leads to a larger portion of the image in focus. More light is required to shoot with a smaller opening in the lens. Alternately, use a wide-angle lens or be further away from the subject.
On the other hand, create a shallow DOF with a large-sensor camera and a large aperture lens that requires less light. Or, consider a longer lens and be closer to the subject.
A shallow DOF produces blurred and out-of-focus areas in a scene. Any highlights in the blurred area create near-circle shapes that resemble the lens aperture blades. These shapes are called “bokeh,” which means, “blur” in Japanese.Some lenses come with DOF markings, but to be doubly sure on how wide your depth will be for a given lens, aperture or subject distance, smartphone DOF apps are handy.
- Depth of field
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