When using your DSLR camera in other than Auto mode, you will need to become familiar with a few concepts that might seem complicated at the beginning, but are a lot simpler than you think. Aperture, Shutter Speed, ISO, White Balance are possibly the most common and also important ones.
Aperture â€“ a window to light
The easiest way to understand the concept of Aperture is to think of what it is in its most basic form: a window. Imagine if you like that your camera is the size of a living room, a living room with no windows (in other words a camera obscura); then imagine that you want to bring in some light into the room, and so most people will think of putting a window in one of the walls.
That will definitely let some light in. And that window, or opening, in a camera becomes your Aperture.
Big window, small window
The size of the window will determine how much light is allowed into the room. A bigger window will let more light in, and conversely a smaller window will let less light in.
In a camera, the size of the aperture will also determine how much light is allowed to come into the camera.
Fortunately, and unlike most windows, the Aperture in a camera can vary in size, and that is pretty handy. It lets the photographer, you, to decide and control how much light is going to come into the camera in order to take a picture.
The diaphragm is the clever device that allows your Aperture to change in size. It is quite simply a series of blades that open and close against each other making the opening in the middle bigger or smaller.
The shape of the opening is pretty close to circular, but it does actually depend on the number of blades in the diaphragm.
What size exactly?
Typically the Aperture is measured in stops, also called fstops, with each full stop letting in half the amount of light that the previous one in the scale. The scale of full stops corresponds to a factor of √2, or approximately 1.4, this means that a circle that has a diameter 1.4 times smaller than another circle, will let in only half the amount of light.
However to make it slightly more complicated, but not that much, the actual scale is an inverse relationship between the actual focal length of the lens to the diameter of the opening in the diaphragm.
Aperture fstop = Focal Length / Diameter of Opening
An Aperture fstop value of 1 will mean that the Focal Length and the Diameter of the Opening are the same size.
For example, if the focal length is 50mm and the diameter of the opening is also 50mm, then the fstop is equal to 1.
If the Diameter of the Opening decreases, i.e. the opening becomes smaller, then the Aperture fstop value will increase.
For example, this time, if the focal length is still 50mm and the diameter of the opening goes down to about 35mm, then the fstop is equal to 1.4.
The full fstop scale will go a bit like this: f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32
Each one being a smaller aperture than the previous one, and letting only half the amount of light.
The smaller the fstop number, for example f2.8, the more light will come into the camera.
The bigger the fstop number, for example f22, the less light will come into the camera.
This scale helps the photographer, you, to decide and control the amount of light that enter the camera.
The Aperture in your camera is nothing more than an opening allowing light to come into the camera. The Aperture opening can be changed in size by the photographer.
A scale of fstops will help the photographer decide and control de amount of light that comes into the camera. Each full fstop value will let in half the amount of light than the previous one on the scale.