Understanding aperture for beginners

Unlike shutter speed and ISO, the aperture has more to do with your lens and than that of your camera body. It is part of exposure and can affect your images in a lot of ways.

Using, the right f stop setting can allow you to capture a landscape photo that is sharp throughout the frame. Or create a nice blurry background that separates your subject.

And the best part? It’s not as complicated as you think. Let’s dig it!

What is aperture?

Aperture is the opening in your lens from which light passes through unto the camera sensor. The bigger the opening, the bigger the amount light that passes through.

The lens’ opening is controlled by the blade-like material you see inside called the lens diaphragm.

Close up photo of a lens showing the aperture and the diaphragm.

Think of it as a window with blinds on it. The window is the lens and the blinds are the lens diaphragm.

The more you open up the blinds, the more light passes through. And that little holes formed by the opening of the blinds is the aperture.

Except that in lenses, there is only one opening as opposed to multiple openings using the “blinds” analogy.

How aperture is measured?

Aperture is represented in f-stops or t-stops. Most photography lenses are rated in f-stop so we’ll focus on f-stops for now.

When you look at your camera settings, you’ll see seemingly random values such as f/1.8, f/2.8. f/4, etc.

These are a mathematical representation of how much light is going to the camera sensor.

“F” stands for the focal length and the numbers corresponding to that is the “f-numbers”.

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

So in the examples given above, f/1.8 is bigger than f/2.8.

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

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 of 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 do have 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.

In Mathematical expressions 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 actually measure the diameter of the lens opening, 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.

How aperture affects the image?

Aperture affects both the exposure and depth of field of your image.

Aperture cheat sheet showing how aperture affects exposure and depth of field.

Bigger aperture means a brighter image and less depth of field. And smaller aperture means dimmer image and larger depth of field.

Let’s have a close look, shall we?

Exposure:

Bigger aperture allows more light to pass through, producing a brighter image.

Using a very wide aperture than necessary can make your image overexposed. You also risk underexposure if you do not use wide enough aperture settings.

Comparison of images taken at different aperture settings to demonstrate the changes in exposure.

The concept of “stops” will come handy when trying to get the proper exposure. It is 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. The example photo above was taken at 1 stop interval.

You want to know more about the concept of stops, check out our article about how exposure works.

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

Depth of Field:

The bigger the aperture, the smaller the depth of field gets.

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.

Infographic showing the front and back out of focus zone of depth of field.

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 wider aperture shrinks this zone while using a smaller aperture expands it.

Comparison of 3 images showing how the depth of field change as you use smaller or bigger aperture.

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

Bigger aperture results in a shallow depth of field while smaller ones give you deeper DoF.

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.

Aperture limitation:

It’s worth noting that the maximum aperture value available at your disposal differs from lens to lens.

For example, some lenses give you a maximum aperture of f/4 only while some give you f/1.4 max.

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

Maximum aperture example on Canon 24-105 L- lens

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.

How to change the aperture setting?

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

For most modern lenses, you can change the aperture setting by using the back dial on your camera.

Some older model of lenses allows you to change the aperture either through the camera dial or at the dedicated ring dial found at the lens.

And a small number of lenses, especially the really old ones only allows you to change the f/stop through the lens aperture ring only.

Conclusion:

Understanding how aperture works give you better control over the exposure and depth of field of your images.

You can get creative with your images just by using playing around the depth of field through the size of your aperture.

Got questions? Do not hesitate to leave us a comment below.

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