The Basics of Aperture

The Basics of Aperture

In simple words, aperture is how wide the hole through which light enters the camera is. It works pretty much the same as the human eye, as it enlarges or shrinks the pupil, depending on the amount of light around us. When it is dark, our pupils open wide to let more light in to allow us to see better, and vice versa. The same applies to the camera’s lens’ “pupil”: a wider aperture allows more light in the camera, whereas a narrower aperture allows less light.

Aperture is probably the most important element of the exposure triangle, because there’s a good chance that this is the variable that you will play with the most when taking your photos, depending on the kind of image you want to produce.

Do you want to learn to get this effect on your photos? Keep on reading!

If you want to learn about the other two elements of the exposure triangle, here are the links to my posts about them:

Shutter Speed

How is aperture expressed?

Aperture is expressed in “f numbers” on your camera and photo editing programs. This means that you will see the aperture value in your camera expressed as “f/4” or “f4”.  The lower the f number is, the wider the aperture, and vice versa. This might sound a bit counter-intuitive, as you might think that larger numbers mean a wider aperture, but it’s the complete opposite. Don’t let it confuse you. In my camera, a Nikon D3400, the display itself helps you understand this: Notice how with lower f numbers the “pupil” looks much wider, and it gets narrower as you use higher f numbers:

Look how wide open that F/3.5 looks like.


Now look at how much narrower the aperture looks like at F/10

To make it easier to remember, imagine the number refers to a fraction: ½ is of course bigger then 1/8, so this might help understand it. The widest apertures are usually between f/1.2 and f/1.8, letting tons of light in, and the narrowest are usually around f/22.

How does aperture affect your photos?

Aperture affects two big aspects of your photos: their exposure and depth of field.

Aperture and Exposure

As I just mentioned, a wide aperture allows much more light into the camera than a narrow one, so this has a direct impact on how bright or dark your photos will be. When shooting in broad daylight, you will be able to use very narrow apertures and still get a properly exposed image.

Madrid Plaza de Oriente
Madrid’s Plaza de Oriente at night. Using an aperture of F/1.8

However, when light grows weaker, it’s ideal to use wider apertures to let more light into the camera and avoid getting dark pictures. As you might also imagine, if you have read my two previous photography posts, you can also adjust the ISO and/or shutter speed instead of using a wider aperture in low light conditions to get a good photo.

This doesn’t mean that you can’t use the widest apertures in broad daylight, but you will need to use very, VERY fast shutter speeds (and ISO at 100, of course). If the shutter speed is not too fast, the image will be way too bright.

Aperture and Depth of Field

You might be wondering what “depth of field” means, am I right? Well, depth of field refers, in simple words, to how the elements that are in front or behind the focused object will look like. When you take a photo, not all the objects in the frame will be in the same plane (at the same distance from the camera). The subject will be at a determined distance, with some elements in the background and some in the foreground.

“Shallow” Depth of Field

A shallow depth of field means that only the focused object (and any other element located at the same plane) will be in sharp focus, and the other elements in the foreground and background will be blurred. It is achieved by using the widest apertures.  The following is a good example of an extremely shallow depth of field: only the area around the cat’s nose is sharply focused. Even the nearby eyes and ears are already a bit blurred. The rest of the cat’s body is totally blurred.

Aperture at F/1.8

This is particularly useful when you want the main subject/object of the photo to stand out, and you achieve this by making it look sharp against a blurred background.

Ponte Vecchio Florence
The slightly blurred background makes us stand out more in the shot.

Portraits are usually shot with wide apertures, because you want the subject to stand out against a not-too-relevant background. By the way, this “visual effect” of blurring the background is known as “bokeh”. If there are some lights behind your subject, the bokeh effect will make them look like this, allowing for some very cool shots!

When shooting with wide apertures you need to be very careful of correctly focusing on the subject you want to focus on. As I said, with the widest apertures only the spot where you focused on (and everything else on that exact plane) will be focused. So, if all the subjects are NOT on the exact same plane, one (or some) of them will be slightly out of focus. Look at this following photo: the background is nicely blurred, but only one of the bottles is sharply focused. This happened because the yellow bottle was slightly further away. As I said, with very wide apertures, only objects on the exact same plane of the focused point will be sharp.

Another thing that could happen if you completely miss the focusing, is that the background will be sharp, and your subject completely blurred, achieving the opposite of what you desired. Look at this example:

gelato pantheon
Focused gelato, blurred Pantheon


Focused Pantheon, blurred gelato.

“Deep” Depth of Field

A deep depth of field means that more (or all) the subjects/objects located on different planes of the photo will be sharp and focused, regardless that they are located at different distances from the camera. This is achieved by using narrower apertures. This is useful when you don’t want to blur out the background and foreground of your image, but rather have everything in focus. For example, when you are travelling and you want to take a photo of yourself against a notorious background (the Eiffel Tower, the Colosseum, a city’s skyline, for example), you’ll probably want those elements on the background to be sharp and recognizable, instead of totally blurred out. If you are shooting a landscape, you might also want most of it to be in focus.

Look at the following photos, shot with wide and narrow apertures, and see how the narrower apertures bring the background into focus:

Aperture at F/2.2. Florence is blurred in the background.
Aperture at F/9. Florence looks sharper in the background.

See how the aspect of the background changes? Another example:

Aperture at F/1.8. The town of Vernazza is blurred.
Aperture at F/10. Vernazza is brought into focus.

So it’s basically up to you to determine how you want your background to look like using different aperture settings! Wider apertures will blur it, and narrower apertures will bring it into focus. If you want to make the background look sharp, you don’t need to go all the way up to F/22. As you have seen, you can bring the background into a good focus using apertures of F/9 or F/10.

However, if you use very narrow apertures, you are letting very little light in, which means that you might need to use a higher ISO or a slower shutter speed to make up for that. If you don’t adjust those values, you’ll get a dark image.

The different apertures on your camera’s lens

The aperture values available to you don’t depend on your camera itself, but rather on the lens attached to it. Even though most (or all) lenses can reach very narrow apertures, not all of them can reach the widest apertures, which produce a greater “bokeh”. Most kit lenses (kit lens = the “basic” lens that usually comes with a DSLR camera) can handle maximum apertures of about f/3.5. Even though the difference might not sound as big, it is a LONG WAY from an f/1.8 aperture. The lenses that can handle these very wide apertures are usually more expensive, especially the ones with pretty wide apertures like f/1.4. When it comes to blurring the background, a wider aperture will provide much more blur.

How to get a great bokeh (even with a kit lens)

The fact that your everyday lens doesn’t have very wide apertures of about f/1.8 doesn’t mean that you can’t blur the background of your images for that sweet “bokeh” effect! You can do it with an aperture of f/3.5, you just need to follow these tips:

– First, use the longest focal length available. I know we have not discussed focal length, so for now I will put it this way: zoom in with your lens as much as possible.

– Second, set the widest aperture possible you can use with this focal length. 

– Third, make sure the subject is very close to the camera, and the background as far away as possible for better results.

If you follow all of these tips, you can get a decent blur in your photos! Look at the following photo, it was shot with my kit lens using an aperture of F/3.8, which is not THAT wide, but still it can deliver something like this:

Making the drink stand out. Aperture at F/3.8

Of course, you would get a much greater blur with a wider aperture, but you can still get some bokeh without spending money on additional lenses.


These are the key points to remember so far:

– Aperture affects a photo’s exposure and depth of field.

– A wide aperture lets more light in = brighter photo.

– A narrow aperture lets les light in= darker photo.

– A wide aperture will blur the background and foreground.

– A narrow aperture will bring more of the background and foreground into focus.

– A wide aperture is ideal for shooting in low light conditions, as it makes it possible to use lower ISO values and faster shutter speeds.

Why NOT to use Auto Mode

If you are trying to blur the background or bring it into focus, you might not achieve it in auto mode. Why? When in Auto mode, the camera will set an aperture that is neither too high nor too low, so you won’t get the desired results. You will either get less background blur than you wanted, or a background that is less focused than you desired.

How to easily set the aperture in your camera?

This is actually pretty easy. You’ll see, most (if not all) DSLR’s have a shooting mode called “aperture priority”. In the Nikon mode dial it is the “A”. When using the aperture priority mode, you will control aperture with the camera’s main dial, and the camera will adjust shutter speed and ISO depending on the light around and the chosen shutter speed, to get a proper exposure.

Mode dial in Aperture priority mode

So, in aperture priority, if you turn the dial to the right, you’ll decrease the aperture (higher f number); and if you turn it to the left, you’ll increase it (lower f number).

The “A” in the top left corner means we are in aperture priority mode.

ATTENTION! As I have been telling you, you should ALWAYS be in control of the ISO you shoot with, and I explained how to de-activate the camera’s automatic adjustment of ISO, and how to adjust it yourself. So, if you follow this advice (which you totally should), when you use aperture priority the camera will only automatically adjust the shutter speed, because you should be in control of both the aperture and ISO.

When to use aperture priority mode

Aperture priority mode is ideal when you want to do one of two extremes: either totally blur the background behind your subject, or bring most of it into focus. If you are trying to blur the background, use the widest aperture possible. If you want most or all of the background into focus, use the narrowest aperture possible.

Only the can of beer is sharply focused.

We are now officially done with the three basic elements of photography! Please let me know if you have any doubts so far before we keep on advancing! On the next post we will do a small recap of the three elements of the exposure triangle, and we will get into how they work together, and which settings to use in different conditions!

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