I decided to talk about aperture first because it is one of the three key elements to arrange the exposure of your photograph (in cohesion with ISO and shutter speed). I do think aperture is the most important one because it has a big effect on how your photograph will look. The whole aesthetic can change by widening or narrowing your aperture. Below I will explain more about the way it works and what effects you can achieve.
First, what is aperture?
Definition of aperture
The aperture is a hole through which light falls on your sensor. The aperture is formed by multiple blades. By moving these blades the aperture can become smaller or bigger. The technical definition of the aperture is the opening in the lens through which light passes to enter your camera.
Aperture is often compared to an eye. The biological equivalent of aperture would be the pupil of your eye. The iris (which is attached to your pupil) can expand or shrink depending on the amount of light, allowing more or less light to pass through your pupil so the “image” you see through your eye is always correctly exposed.
Another comparison that can be made is with a tap. The correct exposure would be represented by a glass. The light would be represented by the beer streaming in the glass. The aperture would be how big the tap is. The bigger the tap (aperture), the more beer (light) can stream in at once. This determines how fast the glass will fill up.
What does the aperture do?
Changing your aperture has a big effect on how your photographs look. It changes both your exposure and your depth of field. If you keep the rest of your settings the same, your photograph will brighten as you widen your aperture, at the same time your depth of field will become smaller, making the background less sharp.
What is depth-of-field?
Depth-of-field is a term often used in photography. By using depth-of-field you indicate how much of your photograph appears sharp. The bigger the depth-of-field, the more looks sharp within your photograph. Typically landscape photographs are made using a large depth-of-field so the photograph is sharp from front to back. If the depth-of-field is small, only a very thin slice of your photograph appears sharp, rendering your fore- and background unsharp. This is a technique often used in photography, especially in portrait photography, macro photography and for example when photographing things like toadstools, these are typical examples.
Your background getting less sharp may sound like an undesirable effect, but in fact, most photographers (especially portrait photographers) often strive for this effect as you put more focus on your subject with an out of focus background. The background will not be a distraction that way. It can also give some “magic” to your photograph.
On the left, you can see an example of a “landscape photograph” with a small depth of field and on the right, you see an example with a big depth of field. The photograph on the left has an unsharp fore- and background while the photograph on the right is sharp from front to back.
Aperture and exposure?
The aperture of your camera has an effect on the exposure of your photograph. You can use the aperture to lighten or darken your photograph. A bigger aperture (smaller f-number) will brighten your photograph while a smaller aperture (bigger f-number) will darken your photograph.
Aperture and depth-of-field?
Aperture does not only affect the exposure, but it also affects the depth of field. In my opinion, this is a very important setting to be able to control as a photographer. The look of your photograph will be very different if you compare the same photograph taken with a wide aperture to a photograph with a small aperture. I do have to note aperture is not the only variable to affect the depth of field. (If you want to know more about what variables affect the depth of field, you can take my course on getting a small depth of field). Keep an eye out on the newsletter to be the first one to know about the release.
When I photograph horses, most of the time I strive for a small depth of field so the focus is on the horse and not on the background. The surrounding can play a good part in the photograph, but with a small aperture, it will not take the upper hand.
A small word of warning
The bigger the aperture does, and with that, the smaller the depth of field, the harder it gets to get a properly focused photograph. When photographing at values like f/2.8 you need to be so very precise to get the correct focus, it can be so challenging, it can become a form of art to even get it right (especially if you are photographing with a full frame camera!).
f-number, what does it mean?
The f-number that indicates the setting of your aperture can be very confusing. With the f-number, you describe how big the aperture is. A smaller f-number indicates a bigger aperture while a bigger f-number indicates a smaller aperture. Isn’t that confusing and counterintuitive? Yes, it is. Until you know the aperture is a fraction.
F2 is 1/2th (in other words, a half). If you look at it that way it becomes better understood. 1/2.8th is bigger than 1/16th. Therefor f/2.8 is bigger than f/16 instead of the other way around.
if another photographer tells you to use a big aperture they mean something like f/2, f/2.8 or f/4, if they tell you to use a small aperture they mean something like f/8, f/11 or f/16.
Tell me how to set aperture!
After learning all this about aperture you of course want to be able to select the aperture yourself. There are two modes in which you can do so, being the manual mode and aperture-priority mode. Aperture-priority-mode is usually written as A or Av. Manual mode is usually written as M.
Often you can switch modes on the camera mode dial button on the top button of your camera. When your camera is in the M or A/Av mode you can usually change the aperture with the round turning wheel near your thumb. Read the manual or look on the internet to see how you can change these settings for your camera.
If your camera has an LCD on top, the aperture will often be displayed there. It might also be displayed on the LCD on the back and if you look through the viewfinder. In the viewfinder, you will most likely see the aperture in the middle of the bottom or on the side of the bottom.
How big can I set my aperture?
How big you can make your aperture depends on your lens. You will be able to find this number on your lens. You can find how small and how big your aperture can become. There are lenses that have the same aperture over its entire range, but there are also lenses with an aperture that may vary when zooming in or out. The lens you see in the left image below has a variable aperture (1 : 3.5 – 5.6) while the lens on the right has a fixed minimal aperture across the entire range (1 : 2.8).
What does this actually mean?
The lens with the fixed aperture in this example is able to photograph with a wider aperture (being f/2.8) while the widest aperture of the other lens is f/3.5 (when entirely zoomed out). When that lens is entirely zoomed in, the widest aperture even becomes f/5.6.
The reason you see 1 : 2.8 is because the aperture is a fraction. f/2.8 means the aperture is 1 / 2.8th of the focal length. How big your actual aperture depends on how far you’ve zoomed in with your lens; if you take a lens on aperture f/4 as an example: if you are at 50mm your aperture will be 12,5mm wide. At 200mm your aperture will be 50mm wide.
Fast and slow lenses?
You may hear a photographer talk about a fast or slow lens. They might not be talking about how fast the lens focusses but rather about how wide the maximum aperture is of the lens.
If you compare a Nikkor 55-200mm f/4 – 5.6 ed VR II with a Nikkor 70-200mm f/2.8 VR II the latter one is the faster lens. In fact, of these two lenses the focus of the latter lens is a lot faster too, but in this case, the photographers are referring to the value f/4-5.6 and f/2.8 of the lenses. f/2.8 is clearly a wider aperture, therefore you can let more light in at once and photograph with faster shutter speed (or lower ISO). This is what makes the lens “faster”.
Firstly, with aperture, you can arrange your exposure. By opening up your aperture (put your camera on a lower f-number) you make your photograph lighter. As opposed to when you close down your aperture (put your camera on a higher f-number) you make your photograph darker.
Secondly, you also arrange depth-of-field with your aperture. A big aperture (small f-number) gives a small depth-of-field and therefore an unsharp fore- and background while a small aperture (a big f-number) gives a big depth-of-field and therefore is sharp from front to back.