Effective Light Metering and How to Use It

 

1. Introduction to Light Metering

In the past, before the advent of automatic Through-the-Lens (TTL) metering in film cameras, how did photographers determine exposure settings? Did they simply guess shutter speed and aperture?

Not at all. They relied on external light meters (see Figure 1), which they used to measure the light intensity on the subject and background (if needed) to calculate the appropriate exposure settings. As you may know, incorrect metering could ruin an image, and in the days of film photography, there was no second chance to fix it. That’s why accurate metering was essential.

Question: Is there a difference between metering in film (analog) photography and digital photography? If so, why should we care?

Answer: Yes, there is. Here’s why:

• Film photography metering measures the light intensity directly on the subject using an external meter.
• Digital photography metering relies on the reflection of light. Light hits the subject, reflects through the lens, and is measured by the camera sensor.

(NOTE: The technical aspects of light metering will be discussed in a separate post if you’re interested.)

Now that we’ve covered the physics, let’s move on to practical metering techniques.

2. Types of Light Metering

Camera manufacturers provide multiple metering modes, but they generally fall into three main categories (see Figure 4):

• Matrix (Evaluative) Metering [ ]
• Spot Metering [ . ]
• Center-Weighted Metering [ o ]

Where are metering values displayed?

They typically appear on the light meter scale in the viewfinder or on the LCD screen, shown as:

+ < - - - - - - - -- - |0- - - - - - - - - -> -

3. How to Use Different Metering Modes

Each metering mode serves a distinct purpose:

• Matrix (Evaluative) Metering [ ]: The camera analyzes light across the entire sensor, assigning around 60% importance to the center and 40% to surrounding areas. It then calculates an average exposure value.
• Spot Metering [ . ]: Measures light only at the focus point, ensuring correct exposure for that specific area, while ignoring the rest of the frame.
• Center-Weighted Metering [ o ]: Measures light primarily at the center of the image. Some cameras allow users to adjust the size of the central metering area. Like spot metering, this mode disregards other parts of the frame beyond the center.

Now, let’s dive into effective metering techniques.

4. Key Steps for Accurate Metering

• Pay attention to the direction of light: How does it interact with your subject?
  • Example 1: A woman sits in a dimly lit room. The primary light source is the sunlight reflecting off surrounding surfaces. If this light is too weak, she will be lost in the shadows.
  • Example 2: If she moves into direct sunlight, the metering focus shifts to how the light falls on her rather than the darker background.

Identifying the primary light source is crucial for accurate metering!

5. The Most Commonly Used Metering Mode

Answer: It depends on the photography style.

Each photographer has their own lighting preferences. Some prefer evenly exposed faces, while others like high-contrast lighting. Proper metering allows for minimal post-processing adjustments, ensuring a natural look.

Personal preference: Center-Weighted Metering [ o ] is my go-to mode for 99% of my shots. Here’s why:

1. Rule of Thirds Compatibility: If you follow the Rule of Thirds, your focal points naturally fall within the center-weighted metering area. Even if the exposure is slightly off by 1-2 stops, it can be easily corrected in post-processing.

2. Natural Vignetting Effect: Many photographers add vignetting to draw attention to the subject. Center-weighted metering often creates this effect naturally, reducing the need for artificial adjustments.

3. Handling Complex Lighting Conditions: When shooting in tricky lighting, why not use spot metering instead? Fortunately, modern cameras have an AE-L (Auto Exposure Lock) button. With center-weighted metering, simply meter the desired area, lock the exposure with AE-L, then recompose the shot.

4. Quick Adjustments with EV Compensation: If needed, the EV (+/-) dial allows for instant exposure corrections, though center-weighted metering usually produces accurate results without extra adjustments.

5. Trust the Light Meter!: A photo that looks dark on the LCD screen isn’t necessarily underexposed. External lighting conditions or screen brightness settings can be misleading. Trust the meter—it’s designed to be precise.

6. Learn to Read Histograms: While histograms provide helpful exposure insights, they aren’t always definitive. The key is to understand the intended mood of the image. Sometimes, a histogram may indicate underexposure, but the image itself looks perfectly balanced.

Conclusion

Accurate metering is the foundation of well-exposed photography. Whether you’re shooting film or digital, understanding and mastering metering modes will help you achieve consistent and professional-quality images with minimal post-processing adjustments.