7 ISO

Focusing on ISO in manual mode

Understanding ISO

To capture the Milky Way above this abandoned schoolhouse, I set the camera to a high ISO of 1600. This increased the camera’s sensitivity to light, allowing it to capture details in the night sky that are typically invisible to the naked eye. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

ISO is one of the three fundamental components of the exposure triangle, alongside shutter speed and aperture. It measures the sensitivity of your camera’s sensor to light. The ISO scale typically ranges from ISO 100 to ISO 6400, with some advanced cameras offering even higher settings. A lower ISO value means less sensitivity to light, producing cleaner images with less noise, whereas a higher ISO value increases sensitivity, which is useful in low light conditions but can introduce noise or grain into your images.

How ISO Works

When you adjust the ISO setting on your DSLR, you are essentially amplifying the sensor’s ability to detect light. This can be particularly useful in various lighting conditions:

  • Low ISO (e.g., ISO 100 or 200): Ideal for bright, well-lit environments. Images taken at low ISO values are typically crisp and clear, with minimal noise.
  • High ISO (e.g., ISO 1600 or higher): Useful in dimly lit situations, such as indoors or at night. While higher ISO settings can help achieve proper exposure without a slow shutter speed, they can also introduce digital noise, which appears as graininess in the image.
In these two images of the same wooden mannequin, taken under the same lighting conditions, you can see the difference between a high and low ISO setting. Notice how the high ISO image exhibits digital ‘noise’ in the darker areas, resulting in a grainy texture, whereas the low ISO image appears smoother and cleaner. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

Using ISO in Manual Mode

Manual mode (denoted as “M” on your camera’s mode dial) allows you to control all three exposure settings: shutter speed, aperture, and ISO. This mode offers the most control and flexibility, enabling you to fine-tune the ISO to match the lighting conditions and achieve the desired exposure.

Switching to ‘M’ for Manual mode gives you full control over your camera’s settings. In this mode, you can make adjustments freely, without the camera automatically compensating for exposure. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

Steps to Use ISO in Manual Mode:

  1. Set Your Camera to Manual Mode and Choose Your ISO:
    Turn the mode dial to “M.” Select your ISO based on the lighting conditions:

    • Bright outdoor settings: Start with ISO 100 or 200.
    • Low-light settings: Start with ISO 1600 or higher.
  2. Adjust Shutter Speed and Aperture:
    Once ISO is set, adjust shutter speed and aperture to balance your exposure. Use the camera’s light meter, visible in the viewfinder or LCD screen, to guide your settings.
  3. Take a Test Shot:
    Review the image on your camera’s LCD screen and zoom in to check for noise and sharpness. Adjust ISO if necessary to improve image quality, especially if you notice too much noise in low light or overexposure in bright light.

Mastering the Light Meter in Manual Mode

When shooting in Manual Mode, you control ISO, shutter speed, and aperture, and the camera’s light meter becomes a valuable tool to help you achieve the correct exposure. The light meter measures the brightness of the scene and suggests settings to achieve an exposure close to 18% gray—a standard reference tone in photography.

However, scenes with predominantly dark or light tones may mislead the light meter. In these cases, it’s essential to trust your instincts and adjust settings manually.

High-Key and Low-Key Photography

The image on the left exemplifies a high-key composition, credited to Robertgombos and licensed under the Creative Commons Attribution-Share Alike 4.0 International license. In contrast, the low-key image on the right was created in my classroom, utilizing a single light source and white powder to capture and reflect the light from the directional beam. The image on the right is a photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)
  • High-Key Images:
    These images are dominated by light tones. For example, when shooting a snowy landscape or a brightly lit portrait, the camera may try to underexpose the scene, as it aims to bring the bright tones closer to the middle gray baseline. In this case, manually increase the exposure to maintain the bright, airy aesthetic of high-key images.
  • Low-Key Images:
    In low-key photography, dark tones dominate the image. Think of a dimly lit portrait or a scene with heavy shadows. The camera will try to brighten the scene, but for a dramatic, moody effect, manually decrease the exposure to keep the dark tones rich and deep.

Both high-key and low-key images can be visually striking and successful, but they require the photographer to ignore the light meter’s guidance and rely on manual adjustments.

Using the Light Meter Scale

This scale displays your camera’s light meter reading, indicating how your current settings will affect the exposure. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

The light meter typically appears as a scale ranging from -2 to +2, with 0 representing the camera’s idea of a balanced exposure. Each number represents a “stop” of light, with -2 being two stops underexposed and +2 being two stops overexposed. Here’s how to use it:

  1. Set Your Aperture, Shutter Speed, and ISO based on your scene and creative goals.
  2. Check the Light Meter Reading: If the meter is centered at 0, the camera believes the exposure is correct for an 18% gray scene.
  3. Adjust Based on Your Intent:
    • For high-key images, the meter may read +1 or +2. Ignore this warning and brighten the scene to achieve the desired look.
    • For low-key images, the meter may read -1 or -2. Again, trust your vision and darken the exposure for dramatic shadows.

Trust Your Eye Over the Light Meter

The technology in your camera is a valuable tool, but nothing can replace your eye, creativity, and the unique vision you have for your image. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

While the light meter is a helpful tool, especially in balanced lighting, it may not give you the results you want for creative scenes. Always trust what you see on your camera’s LCD screen or viewfinder and adjust settings based on the look you want to achieve. Mastering when to rely on your instincts versus the light meter will give you greater control and allow you to produce more compelling images.

Practical Exercise: Using High ISO

Objective: Capture a well-exposed nighttime scene with minimal motion blur.

Equipment Needed:

  • DSLR camera
  • Tripod (optional but recommended)

Steps:

  1. Find Your Location: Choose a location with interesting lighting, such as a cityscape at night, a street with illuminated signs, or a park with decorative lights.
  2. Set Up Your Camera:
    • Switch to Manual mode (“M”).
    • Set your ISO to 1600 or higher.
  3. Adjust Shutter Speed and Aperture:
    • Start with a shutter speed of 1/30s to 1/60s to minimize motion blur.
    • Set the aperture to f/4 or f/5.6 to allow sufficient light.
  4. Compose Your Shot: Frame your scene, making sure elements of interest are in both the foreground and background.
  5. Take a Test Shot: Review the image on the LCD screen, zoom in to check for noise and exposure. Adjust ISO, shutter speed, or aperture as needed.
  6. Experiment: Try different ISO settings and compositions to see how they affect the final image.

Practical Exercise: Using Low ISO

Objective: Capture a well-exposed image in bright outdoor conditions with minimal noise.

Equipment Needed:

  • DSLR camera

Steps:

  1. Find Your Location: Choose a bright outdoor location, such as a park, beach, or garden, on a sunny day.
  2. Set Up Your Camera:
    • Switch to Manual mode (“M”).
    • Set your ISO to 100 or 200.
  3. Adjust Shutter Speed and Aperture:
    • Start with a faster shutter speed like 1/250s to 1/500s to avoid overexposure.
    • Set the aperture to f/8 or f/11 to achieve a deep depth of field.
  4. Compose Your Shot: Frame your scene, ensuring that the subject is well-lit and in focus.
  5. Take a Test Shot: Review the image on the LCD screen, checking for exposure and clarity. Adjust ISO, shutter speed, or aperture as needed.
  6. Experiment: Try different ISO settings and compositions to see how they affect the final image.

Tips for Success

  • Understand Noise: Higher ISO settings can introduce noise into your images, reducing quality. Always aim to use the lowest ISO that still achieves a good exposure. Compare shots with different ISO settings to understand how they affect image quality.
  • Use a Tripod in Low Light: When shooting in low light, using a tripod allows you to keep the ISO low while maintaining sharpness, even with slower shutter speeds.
  • Practice in Various Conditions: Experiment with ISO settings in different environments—indoors, outdoors, daytime, nighttime. This hands-on practice will help you quickly adapt to changing lighting conditions and develop a deeper understanding of how ISO, shutter speed, and aperture work together.

By mastering ISO and learning how to adjust it in Manual mode, you will gain greater control over your photography, allowing you to capture clear, well-exposed images in any lighting condition.

In this image, I used an ISO of 1600 to capture the evening light and the streak of the comet on the horizon. A small red light in the barn’s window adds a point of interest to its silhouette. Shooting in Manual mode allowed me to control the exposure fully, overriding the camera’s light meter, which would have mistakenly brightened the scene. Photo by Eric Demattos CC BY-NC-SA (Attribution Non Commercial ShareAlike)

License

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Learning Digital Photography Copyright © by Eric Demattos is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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