QILONG LIU
qi-long.liu@connect.polyu.hk
Home ⛺️
Papers 📜
Blogs ✍️
Notes 📖
Projects 🏗️
Understanding Exposure | Bryan Peterson
2026-08-28

Understanding Exposure | Bryan Peterson

Exposure triangle

  • Use manual mode so that you can explicitly control the three elements of exposure and ultimately take ownership of your creative choices

    • The light meter indicates the exposure level of the scene: negative values indicate underexposure, while positive values indicate overexposure. Adjust the exposure triangle to achieve the desired exposure level

      [!important]
      The light meter is a guide, not a rule: it assumes the scene is a gray card

  • Exposure triangle
    A one-stop change in exposure doubles or halves the amount of light that reaches the sensor. If you reduce the exposure of one element by one stop and increase that of another by one stop, you largely maintain the same exposure level

    [!tip]
    The nuance is that although multiple combinations of the three elements can achieve the same exposure level, they will produce different visual effects, which will be discussed in the following sections

    • Aperture: f/4, f/5.6, f/8, f/11, f/16, f/22
      The bigger the aperture (smaller f-number), the more light enters the camera, resulting in a brighter image. Aperture also affects depth of field: a larger aperture creates a shallow depth of field, while a smaller aperture increases depth of field.
      • Storytelling composition: f/22
        Front-to-back sharpness, everything in focus, ideal for storytelling
      • Isolation composition: f/2.8, f/4.0, f/5.6, etc.
        Rendering the subject in focus while blurring the background, ideal for isolating the subject
      • "Who cares" aperture: f/8, f/11, etc.
        A compromise between storytelling and isolation, suitable for general photography

        [!tip]
        Usually the image quality is best at f/8 or f/11, and the lens is sharpest in the middle of its aperture range

    • Shutter speed: 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1
      • Freeze motion: 1/1000, 1/500, 1/250, etc.
        A fast shutter speed freezes the motion of a moving subject, ideal for capturing action shots
      • Slow motion: 1/60, 1/30, 1/15, and longer
        A slow shutter speed creates motion blur, ideal for capturing the movement of a subject or creating a sense of motion in a scene
        e.g. traffic, waterfall, etc.
        • Panning: shooting a moving subject with a slow shutter speed while moving the camera in the same direction as the subject, creating a streaking effect in the background while keeping the subject in focus
        • Use a tripod to avoid camera shake when using slow shutter speeds
          P.S. You can use the self-timer feature to further eliminate camera shaking
        • Use ND (natural density) filters to reduce the amount of light entering the camera, allowing for slower shutter speeds in bright conditions
    • ISO: 100, 200, 400, 800, 1600, 3200, 6400
      The sensitivity of the camera's sensor to light. A higher ISO value increases the sensor's sensitivity, allowing for better performance in low-light conditions, but also introduces more noise into the image.

  • White balance

    • The color temperature unit is Kelvin (K). The lower the color temperature, the warmer the light. The higher the color temperature, the cooler the light
    • White balance cancels out a certain level of color temperature to remove the effect of ambient light and reveal the original color of an object

      [!tip]
      Typical white balance value: Daylight: 5500K, Cloudy: 6500K, Shade: 7500K, Tungsten: 2850K, Fluorescent: 3800k

    • The higher the white balance value, the cooler the scene will be. The lower the white balance value, the warmer the scene will be

Natural light

  • Different times of day

    • Golden time: one hour after sunrise and one hour before sunset
      Golden-time light tends to be warm, low-angle, directional, and soft, creating a romantic and dreamy atmosphere
      The morning golden time tends to be cooler than the afternoon golden time
    • Midday light
      Midday light tends to be harsh and unflattering, creating strong shadows and highlights

  • Different lighting angles

    • Front-light
      Front light evenly illuminates the subject, reducing shadows and texture and creating a flat, two-dimensional look. Front light under overcast conditions tends to be even softer
    • Sidelight
      Renders strong shadows and highlights and creates the illusion of three-dimensionality, enhancing the texture and depth of the subject
    • Backlight
      • Creates a silhouette effect, emphasizing the shape and outline of the subject, and can create a sense of drama and mystery

  • Exposure metering

    [!important]
    The 18% reflectance assumption
    The light meter assumes that the scene has an average reflectance of 18%, which is equivalent to a gray card. If the scene is brighter than 18% reflectance, the light meter will underexpose the image, and if the scene is darker than 18% reflectance, the light meter will overexpose the image

    • Gray card +0
      You can use a gray card to measure the exposure of a scene and adjust the exposure triangle accordingly. Place the gray card in the same lighting conditions as the subject and take a reading with the light meter. Adjust the exposure triangle until the light meter reads 0
    • Palm +1
      Without a gray card, you can use your palm to estimate the exposure of a scene. Place your palm in the same lighting conditions as the subject and take a reading with the light meter. Adjust the exposure triangle until the light meter reads +1
    • Sky +1 / +0
      A bright sky is usually brighter than the meter’s middle-gray reference, so metering the sky at 0 may render it darker than it appears. You can adjust the exposure triangle until the light meter reads +1. +0 is also fine if you prefer a deeper, more saturated blue
      • Snow scene
        The snow is usually brighter than 18% reflectance, so the light meter will underexpose the image. You can use the blue sky in the scene to adjust the exposure
    • Green plants -2/3
      The green plants tend to be darker than 18% reflectance. You can adjust the exposure triangle until the light meter reads -2/3
    • Off the "correct" exposure
      The exposure metering tricks above denote how to record the "correct" exposure, i.e., how to best replicate the brightness perceived by human eyes. However, you can also intentionally overexpose or underexpose the image to create a certain mood or effect

      • -2/3 exposure
        This can produce an image with better color saturation and contrast after the exposure is corrected in post-processing

      • ETTR (expose to the right)
        Exposing the image to the right of the histogram by enlarging the aperture or slowing the shutter speed, i.e. increasing the light that hits the sensor and resulting in slight overexposure but without dead whites. It can reduce noise by better utilizing the dynamic range of the sensor

        [!warning]
        This technique requires careful attention to avoid clipping highlights and losing detail in bright areas

        [!tip]
        Only adjust aperture and shutter speed, not ISO -- only the first two affect the amount of light that hits the sensor, while ISO only affects the sensor's sensitivity to light, and a high ISO can introduce noise into the image

  • Special accessories

    • Polarizing filter
      • A polarizing filter can reduce reflections and glare from non-metallic surfaces, such as water and glass, and can also enhance the color saturation of the sky and foliage. It works by blocking certain light waves that are reflected off surfaces at certain angles
      • The effect of a polarizing filter is most pronounced when the sun is at a 90-degree angle to the subject, and the filter should be rotated to achieve the desired effect
      • A polarizing filter can also reduce haze in landscape photography, resulting in clearer and more vibrant images

Electronic flash

  • Exposure with electronic flash

    [!tip]
    First adjust the exposure of ambient light, and then adjust the flash light power output, direction, and distance. Shutter speed does not affect the brightness of the flash light, so it can be used to control the exposure of ambient light without affecting the flash light, until 1/250s.

    • Ambient light
      The brightness of the ambient light is controlled by all three elements of the exposure triangle: aperture, shutter speed, and ISO. If you want the flash light to dominate the exposure, first adjust the exposure to at least -2 underexposure

    • Flash light
      Of the three elements of the exposure triangle, only aperture and ISO affect the brightness of the flash light. Shutter speed does not affect the brightness of the flash light, since the flash duration is much shorter than the shutter speed. Also, the brightness of the flash light is affected by the distance between the flash and the subject, as well as the power output of the flash

      [!important]
      When the shutter speed is faster than the flash synchronization (usually 1/250s), you need to enable the HSS (high speed sync), which will reduce the brightness of the flash light. The HSS mode allows the flash to fire multiple times during the exposure, effectively creating a continuous light source that can be used with faster shutter speeds. Avoid using HSS if possible

      [!tip]
      To adjust the color or temperature of the flash light, you can use color gels or filters. These can be placed over the flash to change the color of the light, allowing for creative effects or to match the ambient light

  • Use cases
    • Fill light
      Flash light can be used as a fill light to illuminate the shadows in a scene, reducing contrast and creating a more balanced exposure. This is especially useful in backlit or high-contrast situations
    • Wireless flash
      Off-the-camera flash can be triggered wirelessly using radio triggers or optical sensors, allowing for more creative lighting setups and greater flexibility in positioning the flash
    • Multiple flashes
      Professional photographers often use multiple flashes to create complex lighting setups, such as key light, fill light, and rim light, to achieve a desired look or mood in the image
    • Motion freezing
      Since the flash duration is much shorter than the shutter speed, it can be used to freeze motion in a scene, even when using a slow shutter speed. This is especially useful for capturing fast-moving subjects or action shots