Tag: Depth of Field

Exposure Triangle

Posted on by P.Brownewell

Exposure Triangle

Aperture, shutter speed, and ISO all work together to create a properly exposed image.

The exposure triangle is a relatively new term first bursting onto the scene somewhere between 2005 and 2010. Before that, it was “time + intensity = exposure.” With digital cameras and their ability to change ISO values, that old mentality went out the window.

The exposure triangle, in my opinion, is meant to teach the concept of equivalent exposures. Assuming that you already have a properly exposed image, when you adjust one setting, you need to adjust something else in an equal, but opposite way.

 

What makes up the exposure triangle?

 

Aperture

Aperture is just a hole that lets light hit some sort of recording medium (film, plate, sensor, etc.). They can be mechanical, like those found in modern lenses or leaf shutters. Or, they can be a simple hole, like those found in pinhole cameras. 

Apertures limit the amount of light which can reach a sensor by increasing or decreasing the size of the hole. Changing the size of the hole will also change the depth of field. (visit the Aperture page for a more in-depth understanding of aperture)

Shutter Speed

A shutter controls the amount of time that light is entering the camera. Like an aperture, a shutter can be extremely simple, like using your hand to cover the lens or a pinhole. Or, they can be very complex like leaf shutters.

All shutters limit the amount of light entering the camera by blocking and unblocking the light entering the camera. Shutter speed also dictates the amount of motion blur present in the final image. (visit the Shutter Speed page for a more in-depth understanding of shutter speed)

ISO

In broad terms, ISO is the sensitivity of the recording medium. The higher the number, the more sensitive the medium.

Unlike film, digital ISO can be changed with each photo. However, like film, the high you set your ISO, the worse the image quality will be. As you go up the ISO scale you will notice grain or noise, especially in the shadows.

Generally speaking, you should use the lowest ISO possible which produces the desired aperture and shutter speed settings. (visit the ISO page for a more in-depth understanding)

Why is it important?

The exposure triangle tells you nothing about what the proper exposure for a photo should be. So what makes it important?

The exposure triangle is all about equivalency. Equivalent exposures are when your photos from the same scene have the same brightness (or density if you’re using film). It is when you change one leg of the triangle, like decrease the aperture, and make up for the loss of light by increasing the ISO or decreasing your shutter speed.

Equivalent exposures become important as you look to control your depth of field through changes in the aperture, motion blur through changes in the shutter speed, or control noise with changes in ISO. Knowing that you have to make an adjustment in the other direction (more or less light/sensitivity) becomes very important to your creative process.

Aperture

Posted on by P.Brownewell

Aperture is:

Put simply, a hole that allows light to reach the recording medium. It can get larger or smaller in nearly all lenses.

 

Aperture controls:

First and foremost, the aperture’s main function is to control the amount of light entering the camera by increasing or decreasing the size of the hole.

Depth of Field:

Aperture is one way to control depth of field. The larger the aperture, the more shallow the depth of field will be. The smaller the aperture, the deeper the depth.

Camera Obscura

The Camera Obscura is simply a light tight box with a hole opposite of the recording medium. Occasionally, they may have a lens.

Aperture basics

In week one, we turned the entire room into a Camera Obscura, a primitive camera. The windows and doors were blackened with paper and a large hole was cut into the paper covering the window. 

This large hole was our aperture.

We used an old screen printing silk to project the image onto so that students could see how the image changed. Using pieces of paper with smaller and smaller holes, students could watch the resulting projected image become sharper yet more dark each time the hole diameter was decreased.

See the photos below for reference:

F-Stops

F-stops is the function of the lens’ focal length divided by the physical diameter of the aperture. For instance, a 500mm lens with a 50mm aperture diameter will be at f/10. A 200mm lens with a 50mm aperture diameter will be at f/4.

F-stops do not change between lenses. What I mean by that is if you have a 28mm lens at f/10 and a shutter speed of 1/60 and you change to a 300mm lens, your settings will not need to be changed (f/10, 1/60th). {note, this may not be exactly accurate because of light transmission properties or T-stops}.

F-Stop

Focal length/aperture diameter = f-stop number and are interchangeable between lenses

Depth of Field

Depth of Field (DoF) refers to how much of an image is in focus from near to far.

Depth of Field as it Relates to Apertures

A large aperture diameter (or lower f-stop number) will let in more light but the image will have a very narrow depth of field. Conversely, a small aperture diameter will create a deeper depth of field but will allow less light to reach the recording media.

For instance, if you are shooting a group of eight people, you will need a deeper depth of field to get them all in focus (a good rule of thumb for group numbers is f-stop = the number of people in the photo). If you are photographing a single person and want to isolate them from the background, a wide aperture will blur the background (bokeh) but keep the person in focus.