Aperture… isn’t it just a hole?
Yes, but it does so much more than just let light in. In manual and aperture modes you can specify the size of the aperture. The numbers that represent this, called f stops, can be confusing however since the smaller f stop number indicates a larger opening. As you’ll see, once you get past that it’s very easy to decide what the best setting is for your use.
There are a few things to think about when you’re considering what f stop to use. If you are in a low light situation you will want to shoot “wide open”, which means you want the smallest f stop, somewhere between f/1.0 and f/4.0 preferably. The lowest f stop available is going to depend on what your lens allows as well as the focal length you are using. A lens with a very low f stop, like f/1.4, is considered a “fast lens”, meaning it can collect a lot of light quickly due to the large aperture. Consequently if you are outside on a bright day, using an f stop of f/16 can tone down the overpowering brightness of the sun nicely. The aperture works hand in hand with the shutter and ISO to make a perfect photo.
Depth of Field
Aside from letting in light, another important function of the aperture is controlling what is called depth of field. Depth of field is just a fancy term for how much of a scene is in focus and it’s primarily controlled by your aperture.
Just to make things a little more complicated the rule for depth of field is the larger the aperture the smaller the area of focus will be. So for example, if you are taking someone’s portrait and you use an aperture of f/5.6 you will have a photo where the person is in focus but the background is a little blurry. This blurry background is called bokeh (pronounced bow-kay) and can create beautiful portraits and macro backgrounds if used well. Remember bokeh is based on your background so if you background is bland your bokeh will be too.
You may not want anything to be blurry however so you might choose a smaller aperture, f/16 for example. This will let you get everything in focus which is perfect for things like landscapes and architecture where you want a large area in focus. There is a caveat to this however. You might think, if I set it to f/32 my images will be super sharp. Not true, unfortunately. Lenses have what is called a “sweet spot” for focus. It can change from lens to lens but generally this sweet spot is between f/8 and f/11. This range will produce the most sharp images, anything larger or smaller and you lose some sharpness.
Have you ever seen a photo where lights appear to twinkle, sending rays out in all directions? This is actually a side effect of the aperture. The aperture of a camera is a series of interlocking blades, as shown below, that shift together to create a circle. These blades have straight edges so it isn’t actually a perfect circle, it has edges. When a light that is significantly brighter than the rest of the scene enters the aperture these edges bend it slightly causing this effect. Any source of light can cause this, from street lights to the sun or even just a reflection in a water drop. The smaller the aperture is, the more rays come off the light source.
That’s it for now on aperture. Next time you’re out with your camera try changing the aperture you’re shooting with to see what kind of interesting effects you can make!