Cameta 101: What is Aperture?


If you’re a beginning photographer, you’ve likely heard the term aperture being thrown around… but what is it? Well, put simply, it’s the opening of the lens.  The size of the opening is measured in f-stops, such as f/2, f/5.6, f/16, etc.  The larger the f-stop number, the smaller the opening of the lens (I know that’s a little confusing). Conversely, the smaller the f-stop, the bigger the opening.  The size of the aperture determines how much light enters the camera, which directly affects your exposure.

How Aperture Affects Exposure

If you’re shooting at a lower f-stop (bigger opening), more light will be let in. In order to have a good exposure, you need to adjust the shutter speed and/or ISO (sensitivity) in order to compensate for the generous amount of light. So, if you’re shooting at f/2.8, a fairly large opening, and you will need to set a fast shutter speed to achieve a good exposure.  This applies to smaller apertures as well.  If you shoot at f/16, you will need a slower shutter speed to let more light in.

Another consideration is ISO, which affects the sensor’s sensitivity to light.  With wide open apertures (f/1.8, f/2) you have more freedom to use a low ISO number, which will give you clearer images.  With small apertures (f/16, f/22), you may have to dial up the ISO, which increases brightness but also introduces noise and grain.  It’s a delicate balance between aperture, shutter speed and ISO, so use manual mode to experiment.

In addition to exposure, your aperture affects your depth of field. OK, what’s depth of field? We’ll get to that, but first let’s look at some examples of pictures taken at different apertures.

F/4.5 APERTURE F/22 APERTURE

Depth of Field

Depth of field refers to the area of your photograph (from the photographer’s point of view) that is in focus.  Portraits typically are shot with a shallow depth of field (low f-stop number), where a small portion of the image is sharp, but the rest is blurry. This is a great way to keep the focus on the subject without being distracted by the background or foreground.

F/4 APERTURE

A deep depth of field (high f-stop number) yields images where almost everything is sharp. I especially like a deep depth of field when I’m shooting landscapes so that the whole expanse is clear and visible. It gives the feeling that you’re right there, in that location.

F/11 APERTURE

Aperture and Lenses

Zoom lenses change focal length which gives you more freedom to zoom in and out to get the best shot. Standard zoom lenses have a maximum aperture range that varies depending upon the focal length. For example, if you have a typical 18-55mm lens and you’re shooting at 18mm, the maximum opening might be f/3.5.  However, if you’re shooting at 55mm, the maximum opening will be smaller, often f/5.6.  Some zoom lenses have a fixed maximum aperture that is constant throughout the entire zoom range, giving you more flexibility at any focal length. These lenses are faster, more refined and more expensive.  The same is true for single focal length (prime) lenses… a 50mm lens with a f/1.8 maximum aperture will likely cost much more than a 50mm f/2.8, but the larger opening can help improve your photos in a number of ways.

Final Thoughts

So, I know that was a lot of information, but it’s important to know. Your aperture controls the amount of light shining on the sensor, and this, in turn, affects exposure, so shutter speed and ISO must be changed accordingly.  All these aspects have noticeable effects on your images.

Still, it’s pretty fun when you have real control over what you can create. For instance, if I want to shoot with a fast shutter speed to capture a motorcycle doing a jump, then I know I want to have a larger aperture (smaller f-stop number) to get a good exposure and to blur out the background. If I want to shoot a sprawling mountainscape, then I want to use a smaller opening (larger f-stop number) to get the entire image in focus.

Remember, aperture does so much more than control brightness.  In the end, it will affect sharpness, grain, depth of field, and even bokeh (another subject for another time), so always keep your f-stop number in mind.  And once you learn how to use your aperture to achieve certain looks, photography becomes even more exciting and fun.

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