The Big Three: Aperture, Shutter Speed, & ISO

Aperture, shutter speed, and ISO all work together to create an exposure. Understanding how they work gives you the ability to manipulate these and produce a wide variety of effects.

The aperture or f/stop determines how much light is admitted into the lens. The larger the f-stop(eg.f/16) the smaller the opening and the less light entering the lens.

Shutter speed controls the amount of time the shutter remains open. A fast shutter speed will freeze motion and a slow one will allow blur.

Aperture and shutter speed are both measured in stops. These stops have an inverse relationship.

The diagram above represents this inverse relationship. A change in one requires a corresponding inverse change in the other. The sensitivity range represents the ISO. Understanding this scale and it's relations will allow you to manipulate these to produce shallow DOF, freeze action, allow motion and blur, and so on.

For example; say you want to capture flowing water but do not want to freeze the water. You want a low ISO, a slow shutter speed, and high f-stop. A slow shutter speed will capture the water flowing and the high f-stop will allow less light in during the longer exposure to prevent blowout.

The aperture setting also plays a large part in DOF, along with a few other factors we will discuss later. A low f-stop 1.4, 2.8 will create a very shallow DOF giving the photo a blurred background while the subject remains in focus.

The ISO setting determines the camera sensors sensitivity. A higher ISO will require less light to produce a correct exposure, however, the higher the ISO the more noise you'll encounter depending on your cameras ability to handle high ISO.

*This is a brief introduction the the big three and will be covered more in depth from here on.


Assignment:
In this brief intro you've learned a little bit about the relationship between aperture, shutter speed, and ISO. For this assignment you can use a person or object but objects work best as they don't move!

Set your ISO 100-200 and make sure the auto ISO is off if this is an available option on your camera.

Set your aperture to the lowest possible f-stop. Look at the light meter and change your shutter speed so that your light meter is reading 0. Write down your settings.

Take another shot of the exact same subject but this time set the aperture to f/8 and make the necessary compensation in shutter speed. Write your settings down again.

Look at both photos, what differences do you see in DOF, lighting, focus? Submit both photos to the Flickr group pool with the settings in the description(shutter speed, aperture, ISO).