In continuation to Understanding Shooting Modes (Part-I) where I described the Auto and Programmed Modes, I’ll explain and illustrate one of the advanced modes called Aperture Priority Mode in this part.
Aperture Priority Mode
This mode lets you choose the aperture (lens opening) and the camera chooses the appropriate shutter speed for proper exposure.
Just like human’s eyes, lens of a camera has an opening called iris that opens and closes according to automatic or manual settings. This in optical terms also referred as “Aperture”. Changing the aperture settings changes the size of the opening which controls the amount of light the lens passes through to the image sensor.
Why to use Aperture Priority Mode?
This mode is used when you want to have control over depth-of-field. This is measured in f-stops i.e. f/1.4, f/1.8, etc. Higher f-stop numbers indicate smaller aperture and vice-versa.
The “f-number” is the ratio of distance from the sensor/ film to the optical center of the lens in your camera. When you buy a lens for your camera, it will have a number on it, something like 18mm, 55mm, 105mm, etc. These numbers are called as focal length.
To put all of this simple, when the aperture of a 200mm lens (focal length) is 50 mm (aperture opening) wide, your f-stop will be f/4, because the ratio of 200/50 equals four. If you “stop down” your aperture to half that size – 25 mm wide – your f-stop will be f/8. (200 divided by 25.) So the “f-number” gets larger as you let in less light.
