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Back to basics: aperture

Aperture is the opening of the lens diaphragm inside the lens. The size of the diaphragm opening in a camera lens dictates the amount of light passing through the sensor inside the camera the moment when the shutter curtain opens during exposure. Sounds complicated? Well immaging this; you are standing behind the window curtains in your sitting room looking at the street. The openning in your curtains is your aperture and the sped of qhich you open and close the curtain is the shutter speed. If you open the curtain and close it quickly, passing cars will look as if stationnedm but if you open the curtains and close them slowly, you will see the cars passing by. The same concept applies here.

Aperture size is usually adjusted in f-numbers or f-stops. i.e. those little numbers engraved on the lens like f22 (f/22),16 (f/16), f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8 etc. f/16 will let in 1X the amount of light than a diaphragm opening of f/22 and so forth; while on the other hand, an aperture of f/4.0 will let in 1X lesser than that of f/2.8 etc.

Always remember that large aperture = small f-stop = shallow depth of field (f 1.8, f2.8, f4, f5.6) whereas small aperture = large f-stop = longer depth of field (f 11, f22, f32)

To blur the background use a large aperture (small f-stop) and get close to your object and zoom in.  For infinite depth of field use a very small aperture (large f-stop) and step further away from your subject or use a wide angle lens.

f/8 to f/11 are often the sharpest aperture f-stops and offer the greatest contrast in exposures.

Large depth of field example: f/11, 1/160 sec., ISO 100

f/1.2 to f/5.6 (depending on your lens) produce a blown away background and thus are great for outdoor portraits.

Shallow depth of field example: f/1.8 at 1/1600 sec., ISO 200