March 29th, 2015
Let's dive into aperture (photo credit at link), one of the three major contributors to exposure. As we discussed in the first post of this series, available apertures are determined by the lens used, and larger (wider) apertures allow more light than smaller (narrower) ones.
Different circumstances require different apertures. Generally speaking, in low light situations, maximum (or close to) apertures are used. That said, lenses are often quite a bit sharper when "stopped up" a few stops above maximum aperture. Additionally, minimum aperture often exhibits diffraction. Most references put DLA (diffraction limited aperture) at f/16 or so. So staying between a stop or two above maximum and f/16 is best for the majority of situations.
In addition to affecting exposure, aperture is also involved in determining depth of field (DOF). Aperture changes DOF by altering the plane of focus, where narrower DOFs have less depth of focus, and so have more blurred areas in front of and behind the plane of focus. Narrow DOF is used primarily for macro and portraiture, and wide DOF is used for landscapes. Wider apertures narrow the DOF, but other factors also affect DOF: focal length (where longer values narrow DOF), camera-subject distance (where shorter values narrow DOF), and subject-background distance (where longer values narrow DOF). For instance, both of the pictures below were shot at f/2.8 and 100mm, but the one on the right had a much further camera-subject distance, contributing to a wider DOF.
Here we see another example, this time with narrow apertures (f/18 on the left, f/11 on the right). However, the one on the left was taken at 24mm, focused in at the hyperfocal distance. Compare this to the picture on the right (200mm, closer camera-subject distance), which has a much narrower DOF.
Questions about aperture or DOF? Contact me directly, or leave your question in the comment section below.
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Hope to see you back next time!