A change in the aperture effects the amount of light that is received by the sensor and therefore the amount of light within a still image. To adjust the amount of light in an image, say perhaps a scene is too dark, opening/increasing the aperture will result in a brighter scene. Doubling the aperture quadruples the exposure. Aperture sizes are measured in f-stops (the size of the aperture reduces the depth of field)
There is another factor that will effect the amount of light let into the image: the lens. A larger aperture is needed for a 100 mm lens and hence a smaller one is needed for a 50 mm lens for example to achieve the same result.
Aperture 2.8:
Aperture 2.8 from Ethan Delaney on Vimeo.
In this video I shot a plasma globe up close. In order to show off the short depth of field of the low aperture, I added water droplets to the outside of the globe to help the glass of the globe stand apart.
Aperture 9.0:
Aperture 9.0 from Ethan Delaney on Vimeo.
In contrast to the other clip above, this clip showcases a higher aperture and therefore the lighting in the clip is hence of a lower key. The ISO was adjusted to make up for some of this lost light. It is clear to see that in this video the plasma is entirely in focus as a result of the added depth of field.
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