What is Aperture in Photography [F-stop, Bokeh, & Aperture Explained]

Aperture is one of the fundamentals of exposure that every beginner in photography needs to know.

You ever wondered how your favourite photographer makes that awesome close upshot? Or perhaps you’re baffled why you can’t seem to get everything sharp for your landscape photo?

Using the right aperture setting allows you to capture a sharp landscape photo throughout the frame. Or create an excellent blurry background that separates your subject.

Learning terms like f-stop, focusing, diffraction can help you a long way and take better photos with your camera. And the best part? It’s not as complicated as you think!

What is Aperture, and how does it works?

Unlike shutter speed and ISO, the Aperture has more to do with your lens and than that of your camera body.

Aperture is the opening in your lens’ diaphragm. This hole allows light to pass into the camera sensor and gets converted into digital data.

Aperture is the opening in your lens’ diaphragm. This hole allows light to pass into the camera sensor and gets converted into digital data.

Think of it as a window with blinds on it. The more you open up the blinds, the more light passes through and received by your camera’s sensor.

It affects both the brightness and depth of field of your image.

 Bigger Aperture means a brighter image and less depth of field. We’ll discuss more on these later.

In the past, you can only adjust the Aperture by twisting the aperture dial in your lens.

In the age of digital photography, cameras now have a way to communicate with the lens. You can easily change Aperture using the dial in your camera. Thanks to electronic connections.

However, it is essential to note that Aperture is a characteristic of your lens rather than your camera body.

What is F-stop?

Each exposure control has its measurements. For Aperture, the values are represented as f-stops or t-stops.

Most photography lenses are rated in f-stop, so we’ll focus on f-stops for now.

F-stop is a system used to quantify the amount of light going through your lens. Examples are f/1.4, f/1.8, f/2.8. f/4, etc. These seemingly random values look confusing at first, but it isn’t complicated.

“F” stands for the focal length and the numbers corresponding to that is the “f-numbers.” You see where I’m going with this, don’t you?

Yes, the f-stop is a mathematical formula used to calculate the ratio between the diameter of your lens’s opening and the focal length.

Now, I don’t want to go geeky on you, so let’s keep this simple:

Lower f-number means full opening while higher f-number means smaller opening.

If you’re satisfied with that, you can skip the next section, but if you’re looking for a little more information, read on.

Why do lower f-numbers mean bigger Aperture?

F-stop is calculated by dividing the focal length over the diameter of the lens’ pupil.

Let me give you an example:

You have a 100mm lens, and the diameter of the pupil entrance in your lens is 50mm. This means you have an f-stop value of f/2.

That would be 100/50 = 2.

But that’s not very practical, isn’t it? After all, we see the f-number values in our camera, to begin with. What we don’t have is the actual diameter of the pupil, right?

So let’s reverse that equation and solve for the diameter of the lens’ pupil instead.

The focal length over the f-number = lens’ pupil diameter. (D = F/f-number) where “F” is the focal length.

Let’s say you have a 100mm lens, and you have the Aperture set at f/2.

Your f-stop setting is saying that the diameter of the “hole” in your lens is around 50mm.

That would be 100 ÷ 2 = 50.

Now, if you measure the lens opening diameter, you should get a measurement of around 50 mm.

But if you set your Aperture at f/4, what would be the answer? That’s right; it’s 100 ÷ 4 = 25. Therefore the “hole” is smaller now.

Aperture and exposure:

Aperture lets you adjust the brightness of your image. Bigger aperture allows more light to pass through, producing a brighter image.

Using a vast aperture than necessary can make your image overexposed. You also risk underexposure if you do not use wide enough aperture settings. The concept of stops” will come handy when trying to get the proper exposure.

“Stops” is simply a convenient way to measure the amount of light you are adding or taking away when adjusting any of the exposure controls.

Every stop of increment doubles the amount of light. While every stop decrements cut the amount of light in half. We recommend that you read our post about the exposure triangle for more information.

Anyway, there’s a little “side effect” whenever you change your Aperture…

How Aperture affects the depth of field:

Aside from the brightness, the Aperture can also affect the depth of field.

Your camera can only focus at its sharpest to only one plane of your image at a time. Let’s call this plane as the focus point.

Everything in front and behind the focus point will gradually lose its sharpness. The field where the elements are still acceptably sharp is the depth of field.

Think of it as a zone.

 

Everything that is inside the zone will be in-focus and sharp, while everything outside the zone will be out of focus and blurred.

Using a wider Aperture shrinks this zone while using a smaller Aperture expands it.

Notice how the object at the back becomes blurred when I used a wider aperture?

There are a few other factors that affect the depth of field. But to keep this article focused, I will not discuss it here. I recommend that you read our in-depth article about the depth of field once you’re done with this.

The point is, you can use Aperture to control the looks of your image. You can even create awesome effects by creatively manipulating the depth of field.

Creative ways to use Aperture: Shallow and Deep depth of field:

An image with very little in-focus elements is referred to as an image with a shallow depth of field, while an image with a very large depth of field is referred to as an image having a deep depth of field.

To capture images with shallow depth of field, you need to shoot at a wider aperture like f/2.8 or below. This will give you less in-focus elements.

Shallow depth of field example.

Focusing on these f-stop settings can be somewhat challenging at first. But it will help you guide your viewer’s eye to your subject by blurring out other elements in your frame.

It also helps create a nice separation of your subject from the background or tell a story in your images.

On the contrary, you will get a very Deep Depth of Field using a very narrow aperture.

Instead of having any blurry parts, you will get an image where everything is sharp. Depending on the type of shot, you will need to be at a smaller aperture like f/8 or above to pull it off.

Deep depth of field example.

If you’re shooting landscapes, focusing at the hyperfocal distance will come in handy. This will allow you to get a sharp focus all the way to the horizon.

Instead of focusing on a single subject in your image, you can have your viewers immerse into the scene.

A quick introduction to Bokeh:

Shallow depth of field is sometimes associated with Bokeh. While this is true, Bokeh is not the depth of the field.

Shallow depth of field is the term given for the very large amount of out of focus parts of the image while Bokeh is the quality of those blurred parts.

While you can certainly create beautiful Bokeh with shallow depth of field, the quality may differ depending on a few other factors.

Most of the resources attribute them to your lens’ build quality. While this is true, creating an image with nice Bokeh depends on more than just your lens.

Things like the colours of your out of focus elements, brightness, the shape of the out of focus elements, your lens’ iris shape, and a few more can also help get better quality bokeh.

This means that you can create beautiful looking Bokeh even with your kit lenses.

Lens Limitation:

Even though you can control the f-stop settings using your camera’s control, the Aperture is a characteristic of your lens rather than your camera body.

The maximum f-stop value available at your disposal differs from lens to lens, whatever camera body you use.

Lens manufacturers always include this information on the lens’ name. You can also see it printed at the front of the lens itself.

Lenses with the maximum aperture of f/1.8 and below are referred to as fast lenses.

Having fast lenses gives is useful for low light situations. Unfortunately, they are a bit more expensive too.

Lens Sweet Spot and Diffraction Limit:

Your lens’ sharpness varies slightly for every f-stop value. This is commonly referred to as your lens’ sweet spot. Lenses tend to capture images at their sharpest in their mid-range aperture settings.

For example, a lens with a maximum aperture of f/1.8 might have a sweet spot at around f/4, while a lens with a maximum aperture of f/4 may capture at its best at around f/8.

But then again, this is not applicable for all lens. You will have to test it by shooting a couple of the same images at different f-stop.

On the other hand, using a very small aperture might degrade the sharpness. This is known as diffraction. Degradation in sharpness usually occurs at around f/11 on most lenses.

 There are other things that can affect the sharpness of your image like camera shake, missed focus, or noise.

For now, don’t get too caught up with sweet spots and diffraction. As you can tell by the example, I had to digitally zoom all the way in just to give a clear example.

As long as you avoid shooting at extremely narrow Aperture like f/16, you should be fine.

Even if you had to shoot at that f-stop, the difference is not that huge.

Unless you plan to print your image on a big canvas or some other professional work where sharpness is very important, it’s really not that big of an issue.

Plus, if you shoot in RAW, you have plenty of room to improve your image’s sharpness and overall aesthetic in post-production.

Aperture Priority:

Aperture priority is a semi-automatic mode of shooting in your camera.

In this mode, you manually select the Aperture. And you let the camera decide what it thinks the best shutter speed and ISO to get the proper exposure.

You can find this on one of the dials in your camera, usually labeled as “Av”(canon) or “A”(everyone else).

Aperture priority has a lot of use cases, which will essentially make your life easier as long as you are shooting with good lighting.

If you’re shooting at a very large aperture setting, your camera will probably use fast shutter speed. This will reduce the camera shake and motion blur resulting in a sharper image.

On the flip side, your camera might use a shutter speed that isn’t fast enough in low-light situations. This will result in a blurry image due to camera shake. Remember, the reciprocal rule?

It might also use a very high ISO, which will give you tons of image noise.

And lastly, auto-focus tends to work slow on low light situations and small apertures. I’d, suggest only use this mode if you have plenty of light available in your scene.

Aperture priority makes shooting so much easier. But if you’re just starting out, I’d suggest ditching this mode for now. At least until you fully understand how each exposure setting affects your image.

In manual mode, you’ll be forced to constantly check your exposure settings. It’s the best way to master the concept of exposure.

Conclusion and quick summary:

Understanding how Aperture works is an absolute must for beginners. It will not only help you get properly exposed shots but gives you a lot more option to get creative.

Let’s do a little recap:

• Aperture affects the brightness and depth of field of your image.
• With each stop of increments, you get a brighter image and shallower depth of field.
• You can get creative with your compositions by implementing a shallow or deep depth of field.
• Focusing will also affect the blurriness of your subject. Make sure to properly set your focus before pressing the shutter release button.
• Lenses have a sweet spot that will render the sharpest image possible. Make sure to experiment with your current lens.
• Avoid using extremely small aperture settings, or you’ll risk lens diffraction. But if you must, you can still fix it on post-production.
• Aperture priority can help you easily control your exposure while still having control over your f-stop settings. But only use it once you are very familiar with the other exposure controls such as shutter speed and ISO.

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