Let's start at the beginning. Everyone in the photography world talks about the "Exposure Triangle".
But what is aperture and how does it effect an image?
A camera’s aperture setting controls the size of the opening in the lens, which then regulates the amount of light reaching the film or digital sensor. It works like the pupil in your eye - when the light level is low, it can expand to let in more light, and when there is a lot of light it can close up tight to prevent too much from getting in.
It also impacts the depth of field, or how sharp the subject of an image is compared to it's surroundings.
We've broken this down into two parts if you wish to skip through:
What the f/stop..?
The apertures are described based on a size scale called f-numbers, or f-stops.
Your camera may have displayed something on the screen like f/5.6 or f/8 when you were taking a photograph. The "f-number" refers to the lens aperture, indicating the ratio of focal length to effective aperture diameter. A camera lens typically comes with a set of marked "f-stops,” settings you can use to select an f-number you wish the camera to use.
The "f-number" is a term used to describe the lens aperture, indicating the ratio of focal length to effective aperture diameter.
Each f-number up or down either doubles or halves the amount of light being allowed in.
Opening the aperture up one stop lets twice as much light through, which makes the picture brighter, while closing the aperture down one f-stop makes the picture darker by cutting the amount of light going through by half.
Measurement of Aperture
The f-stop scale looks a little something like this...
The full range of f-numbers is broader than this, going larger and smaller at either end. Also, some cameras have half or third stop settings in between these - but we don't need to worry about those yet. Your camera should have some or all of the f-numbers on this chart – they are the most common ones used in a wide variety of cameras.
Aperture range
This sounds backward, but the larger the f-number the SMALLER the aperture – and the LESS light is going through it.
The lower the f-number, the larger the aperture opening - this lets more light reach the image sensor or film, resulting in pictures with greater exposures.
Higher f-numbers mean smaller aperture openings, less light reaching the film or image sensor, and pictures with lower exposure.
Depth of field (DoF)
The Depth of Field (DoF) is also controlled by the aperture. Depth of Field is the area that is maintained in sharp focus - the subject of the photo and the in-focus areas before and beyond them. The Depth of Field is influenced by 3 factors:
DoF: The lens aperture
Deep DoF
If you wish to have as much of the scene as possible in clear focus (this is called deep or good DoF), set as small an aperture (f-stop) as the light level will permit – somewhere around f/22. Be sure to adjust your shutter speed to compensate and maintain correct exposure.
An aperture setting of f/22 will bring much more of the picture into sharp focus. Changing the aperture in this way is commonly called "stopping the lens down."
Shallow DoF
If you want to narrow down the sharply-focused area of the picture as close to the subject as possible (known as shallow DoF), set the aperture as wide as possible – about an f/2.8. Once again, you’ll need to adjust the shutter speed to compensate.
If your subject is six feet away from the camera and you use an aperture of f/1.8, the depth of field will be very narrow. The subject you focused on will be very sharp, but everything in front of and behind it will be blurred (not as sharp), or out of focus.
DoF: The lens aperture
So we see that the depth of field changes, depending on the f-number.
A higher f-number broadens depth of field, and vice-versa.
However, recall that aperture is linked to shutter speed - so you can’t change just the aperture number and get the same picture with a depth of field adjustment.
Other factors affect depth of field as well, such as how close to the camera your subject, the size of the lens you are using, and how much zoom or magnification you are using. Experiment with different settings and options, and soon you will begin to get a sense of the effect Aperture has on DoF.
DoF: Focal length
A shorter focal length creates a greater depth of field. The longer the focal length, the narrower the depth of field.
For example, using an average lens of about 50mm, your depth of field will be much greater than using a 200mm zoom lens. That is why long telephoto or zoom lenses of often used when a photographer wants a photograph that has a nice sharp focus only on the subject and is blurry everywhere else. When you use a telephoto lens, you will get a narrow depth of field which isolates the subject from its environment, a common technique in telephoto photography. Portraits also frequently use a narrow depth of field, in order to focus attention on the subject and de-emphasize the background.
DoF: Distance from camera
Another way to affect the DoF is to change the distance between the camera and the subject of the photo.
Increasing the distance increases the depth of field, and reducing the distance narrows it.
A photograph of the same subject taken from 10 feet away will have a smaller depth of field than one in which they were 100 feet from the camera. Photographing a subject at a distance from the camera which is essentially infinite will require the camera to be focused on infinity, and create an infinite depth of field.
For more information on Aperture and Depth of Field, contact us to book a One-on-One Workshop HERE >