Aperture priority mode

Aperture is defined as the size of the whole that allows light into the camera to reach the sensor.

The larger the whole, the more light gets in, the lese time is needed for exposure . If you set up the camera on aperture priority, the shutter speed will be varied automatically to achieve the good exposure. You need to select the Av mode on your camera. Before we move on, we need to understand what the F stops (or aperture values) mean.

The aperture value is usually expressed as a fraction. F2.8 means 1inch/2.8 which translates basically into a hole of 2.54 cm / 2.8 = 0.9 cm which means 9 mm diameter hole. It may not seem that much but this will allow plenty of light for a decent exposure for most of the cameras.

The wides aperture (hole) available on the market is F1.2 = 2.54cm/1.2 = 2.11 cm. Usually these lenses with this wide aperture are quite expensive for the average consumer

In order to understand this mode, you can fix the aperture to f4 or F5.6 for example, set the ISO to 100 and see what happens. The camera will attempt to modify the shutter speed automatically in order to obtain a proper exposure. The issues with this mode is that depending on the light levels in front of your camera, you might get a blurry picture if the camera chooses a slower shutter speed than 1/125.

The aperture is limited by the lens you have. A good lens will be have the maximum aperture up to 2.8.

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