The Landscape Photographer's Complete Guide to f-stop, Aperture, and Depth of Field
Aperture is one of the 3 fundamental components of the exposure triangle that all photographers must understand in order to control exposure in their images.
Aperture is determined by a value called the f-stop, which tells the photographer how much light is entering a lens and reaching the camera sensor to expose the image.
Your camera f-stop allows you as the photographer to control two major things:
- The amount of light that enters the camera lens, allowing you to control image brightness.
- The amount of focus in your images, allowing you to control the depth of field in your images.
What is f-stop, aperture, and depth of field in photography?
In this article, we will go over the technical aspects of how f-stop and aperture work so that you will have a solid understanding of what they are.
Then we will cover how aperture affects exposure and depth of field, so that you can use this setting to have greater artistic control over the photos you take.
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What is Aperture in Photography?
In the most simple terms, an aperture is the opening in a lens through which light passes.
In order to fully understand what aperture is, you will need to understand a little bit about camera lens anatomy and how light passes through a lens.
Light enters through the glass at the front of a lens and passes through the lens barrel (the tube shaped housing which holds the internal components of the lens) on its way to the camera’s body where the light hits the image sensor.
Within the lens barrel is a diaphragm formed by overlapping blades called aperture blades. There are typically five to nine blades in most lenses.
These blades can be opened and closed, causing the diameter of the aperture to become larger or smaller, respectively.
Aperture is the term used by photographers to describe the width, or diameter, of the aperture.
Note: the diameter of a circle is simply the length of a straight line that runs through the center of a circle has both endpoints on that circle. Think of it as the width of a circle. Image credit wikipedia.
A key concept you should take away and understand about aperture is:
- A larger (open/wide) aperture will allow the more light to hit the image sensor and increase image exposure.
- A smaller (closed/narrow) aperture will allow less light to hit the image sensor and decrease image exposure.
By adjusting the aperture size, the photographer can control the amount of light hitting the camera sensor, and ultimately the exposure of an image.
A classic analogy that is often used to explain aperture is the iris and the pupil of the eye.
In the center of the iris (the colored part of an eye) lies the pupil, which is the small black hole in the eye that allows light to enter.
The iris of a healthy eye automatically controls the amount of light passing through the pupil by widening and narrowing the diameter of the pupil.
When light passes through the pupil, it hits the retina at the back of the eye. The retina then converts the light it has received into neural signals that ultimately allow the brain to construct an image - the image being what the eye is looking at.
This is essentially the same way a camera records an image. In this analogy, the iris is the diaphragm composed of aperture blades, the pupil is the aperture, and the retina is the image sensor.
Next, we learn how to numerically describe aperture diameter using the term f-stop.
What Does f-stop Mean?
Often times you will read and hear photographers refer to f-stop and aperture as if they are the same thing, but they are not.
While aperture refers to the hole in the camera lens that allows light to pass through, the f-stop, which is also called the f-number or f-ratio, is the number used to describe how wide or narrow the diameter of the aperture is.
Technically, f-stop is the ratio of the lens focal length to the diameter of the aperture.
The f-stop is calculated by dividing the focal length of a lens in millimeters by the aperture diameter in millimeters.
f-stop = lens focal length (mm)/ aperture diameter (mm)
- If a lens with a focal length of 100mm has an aperture diameter opened to 25mm, the current f-stop will be 4.
- If the photographer opened the aperture to 50mm, the f-stop would change to 2 (100 divided by 50 = 2).
- If the photographer closed the aperture diameter to 12.5mm, the f-stop would change to 10 (100 divided by 12.5 = 8).
The f-stop is written as a fraction in the format f/N, where f is always a “hooked” f and N is the f-stop value.
In the example above, the calculated f-stops of 4, 2 and 8 would be written in order as:
The hooked f stands for focal length and is what identifies the number as an f-stop, rather than a shutter speed or any other setting on your camera.
You may have already noticed that there is a scale of standard f-stops that describe a lens’s aperture diameter.
F-stop scale: f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32
As you can see, the lower the f-stop value, the wider the aperture, and vice versa.
These are the f-stops you will find on most lenses, however, the range of these f-stops will vary between lenses.
Some lenses have a fixed range of apertures, but lenses called "variable aperture lenses" have maximum apertures that can vary depending on the focal length (i.e. where the lens is zoomed in).
Higher-end, professional grade lenses typically have lower f-stops (wider apertures ) than their more affordable counterparts.
Also, lenses with longer focal lengths (e.g. telephoto lenses) usually have smaller maximum apertures than lenses with shorter focal lengths (e.g. wide-angle lenses).
How to Find the Aperture Range of Your Lens
Check the outside of your lens barrel to determine that aperture range of your lens.
Figure 5 shows a variable aperture lens. This means that it will shoot at f/4.5 at the shorter end of the focal length (70mm) and change to f/5.6 at the longer focal length (300mm).
Note: some lenses allow the photographer to choose f-stops at 1/3 "stop" increments. See below to learn about exposure stops (which are different than f-stops). This explains the minimum f/stop of f/4.5 on the lens shown in figure 5, which is 1/3 stop higher than f/4 from the f-stop scale.
The Relationship Between f-stop and Focal Length
Why is f-stop a ratio and not just the measured diameter of the aperture?
We now know that the size of a lens’s aperture determines how much light hits the camera sensor.
However, the intensity of light that reaches the sensor also depends on how far it has to travel through the lens.
The intensity of light diminishes the further it has to travel, and vice versa.
This explains why you might notice the headlights of a car increase in brightness as the car approaches you, and why more distance stars in the sky appear fainter than closer ones (assuming the stars are the same size).
There is a mathematical equation in physics called the Inverse Square Law, which describes this relationship between light intensity and distance. My fellow nerds out there can learn more about it here.
So, this is where lens focal length comes into the equation when calculating f-stop.
When traveling through a camera lens, light has much further to travel to reach the sensor of a 300mm lens than a 30mm lens.
Even if a 300mm lens and a 30mm lens both had aperture diameters set to 10mm, the intensity of light hitting the sensor of the 300mm lens would be less than the intensity of light hitting the 30mm lens due to the fact that the light has to travel 10x further through the 300mm lens in order to reach the camera sensor.
Therefore, we need to factor in both aperture diameter and focal length when calculating f-stop so that the intensity of light hitting the camera sensor is constant across all lenses for each f-stop.
In other words, by dividing focal length by aperture diameter, we can infer that the the intensity of light hitting the camera sensor is the same for two different lenses that have the same f-stop.
For example, say we have have two cameras, one with a 300mm lens and one with a 30mm lens. If both cameras are set to an f-stop of f/11, we can assume the the intensity of light hitting the camera sensor in both cameras is the same, even though their apertures are different sizes/diameters.
How f-stop Affects Exposure
If you have been following along from the beginning, you have learned that:
- The wider you open the aperture of a lens, the more light you will allow through the lens.
- The more light you allow through the lens, the more light hits your camera’s image sensor to expose an image.
- Wider lens apertures correlate to smaller f-stop values, and vice versa.
When you put this all together, you have the following key concept you need to understand about f-stops:
Increasing the f-stop value will reduce exposure in your images, and decreasing f-stop will reduce exposure in your images.
This can throw newer photographers off because it’s a bit counterintuitive. However, if you think about the fact that f-stops are fractions, the fractions are actually getting smaller and smaller as the f-stop value increases.
For example, 1/2 is a larger number than 1/22, so f/2 is actually a larger value than f/22.
f-stops and Exposure Stops
In photography, an exposure stop, or “stop” for short, is a measurement of exposure.
A stop is a term that refers to the relative doubling or halving of the amount of light exposed to the camera’s image sensor.
It’s not a constant measure, rather, it is a relative measure that allows us describe the difference in brightness between two images.
Stops are regulated by adjusting f-stop, shutter speed, and ISO (the exposure triangle) on your camera.
In more simple terms, stops work like this:
- When you increase the exposure of your photo by one stop, you are doubling the brightness of that photo because you are doubling the amount of light reaching the camera sensor.
- When you decrease the exposure of your photo by one stop, you cut the brightness of your photo in half because you are cutting the amount of light reaching the camera sensor in half.
Here we are focusing on how to adjust stops by adjusting the f-stop.
Recall the f-stop scale as shown in figure 4.
When you move from one f-stop on this scale to the next f-stop immediately adjacent to it, you change the exposure by one stop.
For example, when you change the f-stop on your camera from from f/5.6 to f/8 (it’s immediately adjacent neighbor on the scale), you are increasing the exposure of an image by one stop, assuming all other exposure settings (like shutter speed and ISO) stay the same.
Alternatively, when you change the f-stop from f/5.6 to f/4, your are decreasing the exposure of an image by one stop.
Therefore, each f-stop on the f-stop scale above is one stop apart. This concept is illustrated in figure 7 below.
We can also describe multiple stop increases and decreases. For example, if we jump from f/2.8 to f/4, we have decreased the amount of light hitting the sensor by two stops of light.
Often times moving from one stop to the next is called “stopping up” or “stopping down.”
- Stopping up refers to decreasing the f-stop value and increasing the exposure
- Stopping down refers to increasing the f-stop value and decreasing exposure.
Figure 8 illustrates an example of stopping down. For example, if you were to change your f-stop from f/2.8 to f/8, you would be stopping down by 3 stops. Alternatively, if you were to change your f-stop from f/8 to f/2.8, you would be stopping up by 3 stop.
In addition, exposure stops can be measured in 1/2 or 1/3 stops. Some lenses may give you the ability to stop down by 1/3 or 1/2 of a stop.
Figure 9 below shows the full f-stop scale including the f-stops at 1/3 and 1/2 increments between the full stop f-stop scale we have already discussed (the scale shown in figure 4).
Figure 9. Diagram showing full f-stop scale from f/1.4 to f/29. Full stops are shown above aperture. 1/3 and 1/2 stops are shown along the arrows below the apertures.
How f-stop Affects Depth of Field
In addition to allowing you to control the amount of light in your photos, your camera f-stop also allows you to control the depth of field (DOF) in your images.
DOF, in simple terms, refers to how much of your image is in focus.
Technically, DOF is the distance between the closest and farthest object in a photo, both of which are acceptably sharp.
A shallow DOF means that a relatively small part of your image is in focus.
A deep DOF means that a relatively large part of your image is in focus.
Here’s how your f-stop setting affects the DOF of your images:
- the smaller the f-stop, the wider the aperture, the smaller (shallower) the DOF
- the larger the f-stop, the smaller the aperture, the larger (deeper) the DOF
Figure 10 below illustrates this concept.
Aperture Size and Diffraction
Something important to know is that the smaller your aperture gets, the less sharp your overall image will be due to something called diffraction.
Diffraction is the loss of sharpness or resolution at higher f-stops due to the interference of light waves with one another when they pass through a small aperture.
Even the point of focus in your images, which is the sharpest point within the DOF in an image, will lose resolution due to diffraction.
You will notice that the higher the f-stop value gets, the more soft the image becomes as it loses resolution and sharpness.
If you want to find the sharpest aperture of a lens, or the “sweet spot” of the lens as it is often called, count up 2-3 f-stops from the widest aperture of that lens.
For example, if the widest aperture of your lens is f/4, the sharpest aperture will be between f/8 to f/11. A lens with an even wider maximum aperture width at f/2.8 will have a sweet spot between f/5.6 to 5/8.
What is the Best Aperture for Landscape Photography?
Landscape photographers are usually trying to maximize the the depth of field in their images so that they can get everything in the foreground all the way to the distant background in focus.
Let’s say you are trying to get both a flower in the foreground and a mountain in the background of your composition in focus.
While there are many variables that can affect the DOF of your image in addition to your f-stop setting (including where the focal point is and the focal length of your lens), let’s stick with picking the ideal f-stop for this scenario first.
Some landscape photographers, myself included, choose f/8-f/11 for most of their landscape images when they are trying to capture a large scene with a deep DOF.
F-stop values of f/8-f/11 are often the sharpest f-stops on many lenses, because, like I mentioned above, the sharpest aperture of a lens is 2-3 f/stops from the widest aperture on that lens.
This f-stop range also provides adequate DOF for most landscape photographs without introducing diffraction.
Don’t be afraid, however, to stop up or down from this mid-range of f-stops. The key is to test your lenses, experiment, and see what works best for the image you are trying to capture.
If you feel like f/8 or f/11 isn’t providing you with enough DOF, try f/16 or even f/22.
Keep in mind that you will have to slow down your shutter speed and/or increase ISO as you narrow your aperture in order to balance your exposure, so using a tripod will become more important to prevent motion blur.
Note: if you are using f/8 or f/11 and find that your are not getting enough of your image in focus, there are more ways to to increase your DOF other than stopping down to f/16 or higher. Some alternatives include focusing at the hyperlocal distance and focus stacking. This allows you to maintain your lenses sharpest aperture while still getting a deep depth of field.
In addition, you might find that certain scenarios call for stopping up or down from f/8-f/11 in order to balance the exposure triangle while achieving a certain effect in your images.
For example, if you are shooting a moving river and want to achieve the effect of motion in the water, you will have to set a specific, constant shutter speed such as 1 second.
Depending on how how light or dark the scene is, you will have to adjust your f-stop to get a proper exposure, even if that means setting it to f/5.6 or smaller. Again, more advanced techniques such as focus stacking can help you overcome lack of DOF when you can’t adequately achieve it with your f-stop setting.
Stopping up to wider apertures can also give you the ability to be more creative in your landscape photos as it can allow you to isolate your subject from the foreground and/or background.
Other Factors that Affect Depth of Field
While your f-stop setting will give you control over the DOF in your image, there are a few other variables that affect DOF which are important to keep into consideration while shooting.
- The focal length of your lens
- The distance of your subject from your lens when in focus
- The size of your image sensor
It is helpful to have an understanding of how these factors affect DOF so that you can adjust your f-stop in a way that allows you to achieve a desired DOF in your images.
For example, as you will see next, you might want to use a higher f-stop when shooting with a telephoto lens than you would use when shooting with a wide angle lens for reasons related to how focal length affects DOF.
How Focal Length Affects DOF
Let’s first go over the basics of focal length before we tie it in to our discussion of DOF.
According to Nikon,
The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (e.g., 28 mm, 50 mm, or 100 mm).” Source: nikon.com
Most lenses have their focal length (or range or lengths) displayed on the outside of the lens, as shown in figure 11 below. Zoom lenses have a range of focal lengths, while prime lenses have a single focal length.
The technicalities of what exactly focal length is are less important than what is does with regard to how your image look.
The focal length of a lens will determine several important aspects of an image, including your Field of View (FOV), how zoomed in or out your subject appears, and the DOF of an image.
This article focuses on how focal length affects DOF, but you can learn more about how focal length affects your images here.
Here is what you need to know about how DOF affects your images:
- the shorter the focal length, the deeper the DOF
- the longer the focal length, the shallower the DOF
This relationship between focal length and DOF tells us that a 14mm wide angle will have a deeper DOF relative to a 300mm telephoto lens.
However, it's important to note that you won’t see much of a change in DOF between different lens focal lengths until you get into much higher focal lengths, usually in the upper telephoto focal lengths greater than 100mm.
Knowing that a telephoto lens can affect the DOF by making it shallower, how would you adjust your aperture to compensate?
My answer would be to stop down, or increase the f-stop, in order to gain DOF lost by using a telephoto lens.
I typically shoot at f/8 when using my wide angle and standard lenses. But when I start shooting my telephoto lens at 100mm and above, I will usually increase my f-stop to at least f/11 - maybe even f/16 or higher.
Again, this is something that you will have to experiment with using your own equipment to see what works best for your setup and the composition you are trying to capture, but hopefully this gives you a conceptual understanding of how to adjust your f-stop when trying to achieve maximum DOF at a certain focal length.
How the Distance Your Subject Affects DOF
Another factor that can affect the DOF in your images is how close your subject (when focused on) is from your lens.
Here is what you need to know about subject distance and DOF:
- The closer the point or object focused on is to your lens, the shallower the DOF.
- The farther the point or object focused on is to your lens, the deeper the DOF.
Look at the scene in figure 10a, for example. If the photographer focused on the trees behind the deer in the background, she would have a greater DOF in the image than she currently has by focusing on the deer as the subject. This is assuming all other settings remained constant, including f-stop.
If you are trying to change DOF in your image but you can't get closer or further from your subject, the practical solution would be to adjust the size of your aperture.
If your subject is very close to you, for example, but you want to get more of the scene if focus (i.e. increase DOF), you might want to increase your f-stop to deepen the DOF.
How Image Sensor Size Affects DOF
Image sensors come in many different sizes. You camera only has one image sensor, so the size of your camera's sensor is something you will not be able to change unless you get a different camera that has a different image sensor size.
Most DSLRs use either a full frame sensor (36 x 24 mm, equivalent to 35mm film), or an APS-C (22.2 x 14.8 mm for Canon and 23.5-23.7 x 15.6 mm for others).
Smart phones with cameras have much smaller image sensors, which allows manufacturers to keep cameras small and sleek.
Even though you will not be able to change your image sensor size unless you switch between cameras with different sensors, it's worth noting that image sensor size if another factor that affects DOF in an image.
Here's what to know about how image sensor size affects DOF:
- The larger the image sensor size, the shallower the DOF
- The smaller the image sensor size, the deeper the DOF
Note: this relationship is assuming that f-stop, the focus point, and the camera's distance from the focus point are constant.
Remember how getting closer to your subject and increasing the focal length of your lens both decreases DOF, as discussed above?
The reason that an increase in sensor size will decrease DOF is because the photographer has to get closer to the subject they are shooting, or use a lens with a longer focal length (e.g. a telephoto lens), in order to get their subject to take up the same amount of the frame as it would if the photographer was shooting with a camera with a smaller image sensor.
If you want to maintain the same DOF in an image taken on a camera with a large image sensor as one taken with a smaller image sensor, you will have to decrease the aperture size (increase f-stop). This will allow you compensate for the reduced DOF that occurs when using a camera with a large image sensor.
Unless you are ready to invest in many different cameras with different image sensor size, this isn't something that you will have to worry about much since you won't be able to adjust it, but it is still important to understand the whole picture when it come to the factors affecting DOF, and how your aperture can be used to compensate them.
Why You Should Try Shooting in Aperture Priority Mode
As a landscape photographer, you might have heard or read that you should be using aperture priority mode.
This is a semi-manual mode that allows you to manually set the f-stop while the camera automatically sets the shutter speed.
This can be highly useful for a photographer that wants to keep their f-stop setting and DOF consistent (e.g. f/11) from image to image without worrying about setting the shutter speed to get a proper exposure.
For the majority of landscape photographs, the photographer doesn’t have to worry about shutter speed because the scene typically isn’t moving. It makes sense to let the camera take care of that part of the exposure triangle so you don’t have to worry about it.
Note: this doesn’t apply if it is windy and you need to have a fast shutter speed, or if you are trying to achieve a certain amount of motion blur in your images like that from moving water or clouds and need a slow shutter speed. I also doesn’t apply to night/astrophotography.
When in aperture priority, you are usually going to want to have your camera on a tripod so that camera shake doesn’t cause your images to be blurry, especially if your camera automatically sets a slow shutter speed.
How to use aperture priority mode
Aperture priority is usually denoted on your camera as “A” or “Av.”
Once in aperture priority mode, you can manually adjust your f-stop and ISO. You will notice that the shutter speed changes automatically.
Remember, when shooting, it is highly recommended to use a tripod.
Check your cameras manual for the specifics on how to set aperture priority mode. Many camera’s, including my Nikon D850, have a dial on the top left which gives you the option to change camera modes from automatic, to manual, or to aperture priority.
- Aperture and f-stop are fundamental part of understanding image exposure.
- An aperture is the opening in a lens through which light passes.
- By adjusting the aperture size, the photographer can control the amount of light hitting the camera sensor, and ultimately the exposure of an image.
- Aperture diameter is adjusted by choosing an f-stop value.
- f-stop is the ratio of the lens focal length to the diameter of the aperture. It is calculated by dividing the focal length of a lens in millimeters by the aperture diameter in millimeters.
- The lower the f-stop value, the wider the aperture, and vice versa.
- Increasing the f-stop value will reduce exposure in your images, and decreasing f-stop will reduce exposure in your images.
- Each f-stop value on the f-stop scale is an exposure stop apart.
- A stop is a term that refers to the relative doubling or halving of the amount of light exposed to the camera’s image sensor.
- Depth of Field (DOF) is the distance between the closest and farthest object in a photo, both of which are acceptably sharp (i.e. how much of your image is in focus)
- DOF has the following relationship with f-stop: the smaller the f-stop, the wider the aperture, the smaller (shallower) the DOF; the larger the f-stop, the smaller the aperture, the larger (deeper) the DOF.
- Diffraction can cause your images to lose resolution at higher f-stops (smaller apertures).
- Camera lenses are typically sharpest at 2-3 f-stops above their widest aperture.
- Landscape photographers often choose higher f-stop settings that maximize the DOF in their images.
- The focal length of a lens affects the depth of field in your images in the following generalized way: the shorter the focal length, the deeper the DOF; the longer the focal length, the shallower the DOF.
- Aperture priority mode is a semi-automatic shooting mode that will allow you to keep your f-stop setting and DOF consistent (e.g. f/11) from image to image without worrying about setting the shutter speed to get a proper exposure.