Let's move beyond full-auto on your DSLR! Part 3: ISO Sensitivity and Other Functions

Part 3 of "Moving Beyond Your Digital SLR's Full Auto Mode" focuses on "ISO Sensitivity and Other Functions." 

Part 1 covered "Aperture," Part 2 "Shutter Speed," and Part 3 will cover "ISO Sensitivity and Other Functions."

The 3 Basic Elements: Aperture, Shutter Speed, and ISO Sensitivity

A "photograph" is composed of three elements: aperture, shutter speed, and ISO sensitivity.

These are mechanisms and functions for obtaining the appropriate amount of light.

It is also necessary to fully understand these elements to freely manipulate light.

Exposure

The amount of light required to compose a photograph depends on the location and brightness, which is called "proper exposure."

"Exposure" refers to applying light to the image sensor (formerly the film surface) during shooting. (Also called illumination)

Exposure is determined by the values of aperture, shutter speed, and ISO sensitivity.

Basically, you set the aperture or shutter speed, and ISO sensitivity acts as a supplement.

About Camera Modes

There are roughly four camera modes: "P, A, S, and M."

This is an example. The settings vary depending on the camera model.

P = Program Mode: A mode that automatically determines the exposure. This mode is suitable for beginners as it does not require difficult operations.

A = Aperture Priority Mode (also called Av on some models): A mode where you set the aperture yourself, and the camera automatically determines the shutter speed to achieve proper exposure.

S = Shutter Speed Priority Mode (also called Tv on some models): A mode where you set the shutter speed yourself, and the camera automatically determines the aperture value.

M = Manual Mode: A mode where you manually set the aperture value, shutter speed, and ISO sensitivity to achieve exposure. Suitable for advanced users.

ISO Sensitivity

With film cameras, the sensitivity is determined by the film loaded. If you load 400 ISO film, you cannot change it until the roll is finished.

In contrast, digital cameras use an image sensor, so you can change the ISO sensitivity at any time, depending on the camera's performance.

Changing the ISO sensitivity expands the range of aperture and shutter speed control.

For example, if the sensitivity is 100, F5.6, and shutter speed is 1/30, and you don't want to stop down the aperture any further but want to prevent blur:

By increasing the sensitivity from 100 to 400, it becomes possible to capture 2 stops more light, so you can increase the shutter speed by 2 stops to 1/125.

50・100・200・400・800・1600・3200

←Low (Dark) / High (Bright)→

←Less Grain / More Grain→

A characteristic of ISO sensitivity is that increasing it makes the image brighter, and decreasing it makes it darker.

Also, the higher the sensitivity, the more noise (graininess) occurs, degrading image quality.

Remember that increasing sensitivity allows you to shoot in dark places, but image quality deteriorates.

How should I set it?

For this item, it's generally OK to set it to auto. (Around 1600 is recommended as the upper limit)

You might increase it in very dark situations, but in such cases, using a flash might yield cleaner results.

Exceptions include aquariums where flash cannot be used, or concerts in dimly lit indoor venues...

In these situations, it's better to increase the sensitivity to achieve a faster shutter speed.

Modern cameras have evolved

Other Convenient Camera Functions

To move beyond relying solely on the camera's full auto mode, we've looked at exposure, aperture priority mode, and shutter priority mode.

In this section, we'll introduce some convenient functions found in many cameras.

AF (Autofocus) Modes

• AF-S...Single AF. Once you focus on a subject by pressing the shutter button halfway, the focus remains locked on that spot as long as you hold the button down. If the subject moves, it will go out of focus. This is suitable for shooting still subjects such as landscapes, flowers, and product photography.
   
• AF-C...Continuous AF. When you focus on a subject by pressing the shutter button halfway, this mode continuously adjusts the focus according to the subject's movement. This is suitable for shooting moving subjects such as animals, children, and sports.
   

AF Area (Focus Area) Settings

When using AF to automatically focus, the camera automatically identifies the subject.

The function that allows the camera to recognize the subject is the AF area setting (the name varies by manufacturer).

• Auto Area AF (Wide)
  A mode where the camera automatically determines what to focus on based on the shape and color of the subject.
   
• Zone AF
  A mode where you specify a range, and the camera automatically identifies the subject within that range.
   
• Single AF (Center)
  You select one specific AF area to focus. In the case of Center AF, the focus is on a single point in the center. This is combined with AF-S mode.
   
• Dynamic AF Area
  Similar to Single AF, you select a specific point. This mode allows surrounding focus points to continue focusing on the subject even if it temporarily moves out of the selected focus point. For this reason, it is suitable for moving subjects.

Exposure Compensation