What is Aperture? The very technical term- "A space through which light passes in an optical or photographic instrument, especially the variable opening by which light enters a camera."
In other words, the opening in the lens that can be adjusted to let more or less light into the camera. It is the third part of the exposure triangle and works with the other two, shutter speed and iso, to create a perfect exposure.
Aperture is like the iris in your eye. As you move between bright and dark environments, the iris will expand or shrink to control the size of the pupil and determine how much light to let in. Usually at an eye exam, your eyes are dilated. You leave the appointment with sunglasses because if you walk out into the bright sunlight without them you will be blinded by the light! Why? Because the opening is so large. Which means, a lot of light is getting through.
Does the size of the aperture do anything else besides affect the amount of light entering?
Yes! Depending on what type of effect you are trying to achieve with your image, you can use a smaller or larger opening to accomplish that.
Aperture can affect your photos by giving your background a "blur" effect called bokeh, or it will give you a sharp image from the front to back with everything in sharp focus.
Usually, for portraits, a shallow depth of field is wanted. Meaning, the bokeh effect. You want your subject to stand out not the background. On the other hand, if you are photographing a scene and want everyone and everything in it to tell the story, then you will want a larger depth of field. You want sharp focus from front to back.
So, your aperture settings will determine the type of image you are creating. Along with shutter speed and iso.
How does the aperture open?
If you look closely at the image below, you will see the small hole in the lens and blades that surround it. These will open and close and change the size of the aperture. Some terms you will hear are "stopping down" and "opening up" your aperture. That basically means, closing the aperture down or making the hole size smaller, and opening it up, or making the hold size bigger.
What do the numbers mean?
If you look at your camera, you will see aperture as f/8, f/4, f/2.8 and so forth. The "f" means f stop or focal length and is the ratio of the lens focal length to the diameter of the entrance pupil. Which basically means, f-stop is the number that your camera shows you when you change the size of the lens aperture and has a certain area that will allow a certain amount of light in to produce a certain effect on your image.
The F is basically a fraction. You can view the aperture f/8 as 1/8. An aperture of f/2 is equal to 1/2. An aperture of f/16 is 1/16 and so forth. It can get confusing as the larger numerals actually have a small opening. 1/2 is larger than 1/16 in the fraction world. So, think of it that way!
So, if f/2 (or 1/2) is larger than f/16 (1/16), which one will let more light in? If you guessed f/2, you are correct. The larger the F number, the smaller the opening, and the smaller the F number, the larger the opening!
If you look at all the f stops, you will notice the size of the opening. Each step down or making the opening smaller, which means going to a higher f number, lets in half the light. (not including f/5.6 or f/2 as those are not the standards) Who knew there was so much math in photography?
So how does aperture work with ISO and Shutter Speed?
As mentioned in the past posts, they all work together to create a great exposure. If you change one, you should change at least one of the other parts.
For example, aperture allows you to create a soft focus (bokeh) portrait by using a large aperture (small number such as f/2.8, but large opening) so you would need to change your shutter speed and/or ISO in order to be sure you are not letting too much light in.
If you wanted to create a beautiful portrait with a soft background at f/2.8 outside with a lot of light, what would you do? Remember, ISO is the sensitivity of the camera's sensor to the light. A low ISO such as 100 would be less sensitive than 400. So, use 100. Shutter Speed is the opening and closing of the "curtains' in the camera that allows a certain amount of light in. If you wanted less light to come in because you were using an f/2.8 aperture, you would want the curtains to close quickly. If you used a FAST shutter speed of 1/800, the 'curtains' would close FAST so LESS light would enter. You might then have a great exposure!
The above image was taken outside in bright light. I wanted the background to be soft and the subjects to be in focus. Since there are three people in the image, using a very large aperture of f/2.8 would have caused two of the people to be in soft focus. (this is another consideration when using a large aperture.) So, I chose f/5.6 and was still able to create a soft focus background while keeping most of the subjects in focus. My ISO was 100 and my shutter speed was 1/400 or higher.
There are other considerations when choosing which aperture to use, though.
Other things to consider are how many subjects are in the image, how far away you are from your subjects and what lens you are using.
We will not go into too much detail on this post, but consider the above image. There are five people. If I wanted to blur the background and chose an f/2.8 aperture, most likely four of them would not be sharp, or in focus. My background would look great, though!
Since a large aperture (small number, big opening) has shallow depth of field ( how focused the image is from front to back), then most everyone and everything around where I focused would be soft.
If I still wanted to blur the background a bit, I could go up to a smaller aperture (larger number, smaller opening) which would still provide a somewhat blurred background with all my subjects being in focus.
I used an f/7.1 aperture, ISO was at 200 (somewhat shady area), and my shutter speed was 1/100. I needed a bit more light. If I had wanted to make sure everything was sharp tack in focus, I would have used a much smaller aperture such as f/22. (small opening, large number)
But then I would have had to up my ISO to at least 800 and used a tripod or external flash to add more light.
What do you think I did for the above image? What could my settings have been?
As you can see, there are many things to consider when creating images. Knowing the exposure triangle and it's parts and how they all work together is a great first step. Just get out and practice with your camera because that is a great way to learn. Write down what your settings were for each image and go back and review them.
If you take photos of the same image with different settings, you will see a difference. For example, find one object. Set your shutter speed to ISO 400. Set your shutter speed at 1/100. Then, start with f/2.8, change to f/4, change to f/8 and so forth and see the differences in each image. Do you need to change your ISO and/or shutter speed to let in more or less light?
Experimenting with different settings will help you understand how everything works together! And, practice is the best way to do that!