What is the aperture? Technically, it is the mechanism inside the camera that allows you to change the amount of light passing through the lens by changing the size of opening—lens aperture.
Think of it functioning like a valve on a water pipe: Wide open, wide aperture, or “opening up” means more light is coming into the lens. Closing or restricting valve, using a smaller aperture, also called stopping down, allows less light into the lens.
Typically, in a broad example, when you have bright conditions (lots of light), you use smaller apertures (stop down)
And when you are in low light situation, you use a wider aperture, or open up.
The Aperture size is described by the term f/stop. The f/stop is numerical value indication that is RELATIVE to the size of lens opening.
The common, full f-stop numbers are: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32
Here’s where apertures and f-stops get confusing …
A smaller f-stop number, such as f/2.8, actually has a larger opening allowing in more light. Likewise, a larger f-stop, such f/22, actually has a smaller opening allowing in less light.
Don’t worry if you are confused. Trust me that this will become second-nature over time.
So what do these f-stop numbers mean? Well, changing the f-stop, for example from f/16 to f/22, is one stop of light change. Now each change of one stop is either ½ or twice the amount of light from the previous f/stop.
For example, if you are at f/8 and you go to f/11, you just cut the amount of light going through the aperture by ½. And if you go from f/8 to f/5.6, you just doubled the amount of light going through the aperture.
The last point I want to touch on is that on most DSLR cameras, each click of the aperture dial is not one stop of light, but actually 1/3rd of a stop of light change.
And guess what…this same “one stop of light change” either doubling or halving the amount of light is also how it works for shutter speeds. If you go from 1/60th to 1/125th (a faster shutter speed), that is a one-stop change and you just cut the amount of light in half. Likewise, going from 1/60th to 1/30th (a slower shutter speed) lets in twice the amount of light.
Changing the aperture also affects the depth of field, which is how much of the scene, going from front to back, is in focus. We’ll talk more about DOF in upcoming episodes.