Workshop – Exposure

The Exposure Triangle

The foundation of manual control is the Exposure Triangle, which consists of three interconnected settings that govern the light reaching the sensor:

1. Aperture: This is the size of the lens opening, controlled by f-numbers (f/stops).
   • Control over Light: A smaller f-number (e.g., f/2.8) is a wider opening, letting in more light.
   • Creative Effect: Aperture directly controls Depth of Field (DoF). A wide aperture creates a shallow DoF, isolating the subject against a blurred background (bokeh). A narrow aperture (e.g., f/16) creates a deep DoF, keeping both foreground and background sharp. Kevin also discussed how DoF can be altered by distance between the Camera and the subject, and the focal length of the lens. The closer the subject is to the camera the smaller the depth of field. This is also true when using a longer focal length.
2. Shutter Speed: This is the length of time the sensor is exposed to light.
   • Control over Light: A slower shutter speed (longer duration, e.g., 1/4 second) allows more light in.
   • Creative Effect: Shutter speed controls Motion. Fast speeds (e.g., 1/1000 sec) freeze action, while slow speeds create deliberate motion blur for effects like smoothing water or capturing light trails.
3. ISO: This represents the sensor’s sensitivity to light.
   • Control over Light: A higher ISO (e.g., ISO 3200) makes the sensor more sensitive, requiring less light from the aperture and shutter.
   • Creative Effect: Higher ISO settings introduce noise or grain, reducing image quality. The primary goal is to use the lowest native ISO (often 100 or 200) and only raise it when the lighting conditions demand it.

Beginning to Override the Camera

Since the camera always defaults to 18% grey, the photographer must manually override this target when shooting scenes that are either intentionally Hi-Key or Lo-Key.

• Exposure Compensation: This feature is used to instruct the camera to brighten or darken the exposure from its initial metered reading.
  • For Hi-Key scenes, the photographer should apply a positive compensation (e.g., +1 or +2) to ensure the white subjects are rendered white.
  • For Lo-Key scenes, the photographer must apply a negative compensation (e.g., -1 or -2) to ensure the dark subjects are rendered black.

Then there was a set of exercises for everyone to practice the skills discussed.

Jargon

• Focus Stacking: This is used when a deep depth of field is wanted, but impossible to achieve in a single shot. The photographer takes multiple images, each focused at a different distance from foreground to background. These images are then combined digitally in camera or in software to produce a final, highly sharp photograph with an impossible depth of field.
• Bracketing: This is used when the amount of visible light exceeds what the camera sensor can register in a single image. The photographer takes multiple images with different exposures to capture the detail in the darkest areas, through to the brightest areas, without clipping. The images can be combined in camera or in post, using software to produce the final High-dynamic range (HDR) image.
• Hyperfocal Distance: A technique for Landscape photography designed to maximise overall sharpness in a single frame. The photographer focuses at a specific point between the nearest foreground and the distant background. This calculation ensures that everything from half that distance to infinity is acceptably sharp. A rough guide is to focus approximately one-third of the way into the scene.
• Zone Focusing: A technique best suited for Street photography where speed is paramount. The photographer pre-sets the lens to a narrow aperture (like f/8 or f/11) and pre-focuses on a specific distance (e.g., 8 feet), manually or using back-button focussing. This creates a predictable zone of acceptable sharpness (e.g., 6 to 12 feet) where the photographer can shoot instantly without waiting for the autofocus to lock the setting.