THE BASICS OF EXPOSURE PART 1-FILM SPEED

Creating images with your camera requires effectively managing light to allow film or a digital sensor to record an image. Three primary settings control the amount of light. Film speed, or ISO, deals with film’s sensitivity to light. The aperture, often discussed in f/stops, is the opening of the lens to allow light to reach the film or sensor. Shutter speed is the time the camera allows light to reach the film or sensor. In this series of articles, we will look at how each component of this exposure triangle works and how to understand and use each setting to create your image. You must understand how each works and how they work together. For these discussions, the term film can be interpreted as traditional film or a digital sensor.

As we discuss these topics, we will do so in simple terms. I will break each piece down into small, easy-to-understand pieces. Film and digital cameras use technically different means to achieve ISO “sensitivity,” but the effects are the same. The purpose of these articles is to help you understand how to improve your photos quickly and get you out shooting images that you love. The camera is a tool; we will not delve into its marvelous engineering now.

TERMINOLOGY:  One term that you will hear regularly is “Stop.”  A Stop is simply a doubling or halving of the light reaching the film or sensor. 

ISO

On your camera, you will see an ISO setting. This can be in the camera’s menus, or on many film cameras, it can be a dial with numbers that can be chosen. ISO settings on cameras typically range from a low of 25 to 200, and a high of 6400 on up to 12800 or higher. The higher the number, the more sensitive the film is to light. To better understand Stops and ISO, think of what each number means. An ISO of 200 is twice as sensitive as 100, and 400 is twice as sensitive as 200. Each doubling is a Stop.

WHY CHANGE THE ISO?

Changing the film’s sensitivity can allow you the flexibility to shoot in different lighting conditions. If it is dark, it will be harder for the camera to collect enough light to create an image. On bright days, the camera will quickly collect enough light. Higher ISO settings can allow you to collect more light in a given amount of time. Lower ISO settings collect less light in the same amount of time.

The clearest images are frequently produced when the ISO is low. Higher ISO can lead to grainy images that look unsharp. With digital photos, this graininess, or pixelization,  is also known as noise. This is the trade-off. Always use the minimum ISO numbers possible, depending on your light and other camera settings.

AUTO ISO

Many cameras allow you to choose AUTO ISO. This will enable the camera to select the ISO based on the amount of light and other camera settings. This is a great tool to use as you learn to manage shutter speed and aperture, but it is best to watch what the camera chooses to avoid grainy surprises. Some cameras allow you to limit the maximum ISO when using the auto settings. This can be helpful to prevent the camera from choosing an ISO that is too high to create clear images without excessive grain or “noise.”