Beginner Tutorial – Aperture

I’d like to kick off with one of the more confusing components of any digital SLR camera, aperture. Aperture isn’t even really a feature of the camera: it’s a feature of the lens. It is a measurement of the opening in the lens. This opening allows light to pass through the lens – that light eventually strikes the digital sensor, which then captures an image. The aperture of a lens is never completely closed: it is always either narrow or wide open. Furthermore, aperture is a variable setting that can be adjusted by the photographer.

Back in the good old days of manual film SLR cameras, aperture was always set by turning a ring on the lens (right where it attached to the camera). Today, this mechanical system has been replaced with an electronic one.Many modern digital SLR lenses no longer include an aperture ring. This is because with a digital SLR, you set the aperture using the camera body: electronic contacts allow the camera to communicate with the lens so when you select an aperture on the camera, it adjusts the lens aperture accordingly.

If you do happen to have an older film lens that is compatible with your digital SLR, you will have to lock the aperture ring on the lens (this is often done by turning the ring to the narrowest lens aperture). Once the aperture ring is locked, then the camera will be able to communicate properly with the lens.

Now for the fun part: the aperture numbers themselves. Part of the fun is that in order for them to make sense, you have to think of aperture numbers as fractions, even though they aren’t displayed that way. Here’s why: the larger the aperture number, the smaller the opening in the lens. Aperture numbers follow a pretty typical scale, and you can always tell when an aperture number is being referenced because it starts with “f/”. The aperture scale goes something like this:

f/2.8, f/4.0, f/5.6, f/8, f/11, f/16, f/22

From left to right, the opening in the lens is getting progressively smaller. An aperture of f/2.8 means the lens is wide open, while at f/22 it is quite narrow. This is why thinking about apertures as fractional numbers might help (unless you’re really bad with fractions). For example, if you compared the fractions 1/4 and 1/22, 1/4 is the larger of the two and therefore represents a larger opening of the lens. This is enough aperture numerology for now. In the next post, I’ll tackle the issue of stops of light and will describe how the standard aperture scale can be broken down further.

By kind permission of Chris Roberts of