Every photograph is an exercise in light measurement. Understanding how your camera meters light — and when to override it — is fundamental to consistent exposures.
This guide covers the basics of light metering, the Sunny 16 rule, and how to work with your camera's built-in meter (or without one).
This guide assumes you've completed:
- Exposure Fundamentals — understanding aperture, shutter speed, ISO, and stops
How Light Meters Work
All light meters measure the same thing: how much light is present. They differ in what they measure:
Reflective Metering
Your camera's built-in meter is reflective. It measures light bouncing off the scene toward the camera. This is convenient but has a fundamental limitation: it doesn't know if it's looking at a white wall or a black cat.
The 18% grey assumption: Camera meters assume the scene averages out to middle grey (18% reflectance). They suggest settings that would render the scene as middle grey. This works well for average scenes but fails on extremes.
- Snow scene: Meter sees bright, suggests underexposure → snow renders grey
- Black dog against dark background: Meter sees dark, suggests overexposure → dog renders grey
Incident Metering
Handheld incident meters measure light falling on the scene, not reflecting from it. You hold the meter at the subject position, pointing toward the camera. This ignores subject reflectance entirely.
Incident metering is more accurate for controlled situations (portraits, studio) but requires a separate meter and physical access to the subject position.
Camera Metering Patterns
Modern cameras offer different metering patterns. Understanding these helps you predict when the meter will get it right (and wrong).
Centre-Weighted
The classic pattern: meters the whole frame but emphasises the centre circle. Predictable and reliable once you understand its bias.
Strengths: Good for centred subjects, easy to anticipate, consistent Weaknesses: Fooled by bright/dark frame edges, backlight
Spot Metering
Meters a tiny area (typically 2-5% of the frame), usually the centre point. Gives you precise control over what you're metering.
Strengths: Precise, excellent for tricky lighting, essential for zone system Weaknesses: Easy to meter the wrong thing, requires understanding of tonal placement
Matrix/Evaluative
Modern pattern that analyses multiple zones and compares to a database of scenes. Sophisticated but unpredictable — you can't easily anticipate its decisions.
Strengths: Often nails exposure automatically, handles complex scenes Weaknesses: Can't predict its choices, sometimes makes odd decisions
The Sunny 16 Rule
Before relying entirely on your meter, learn Sunny 16. It provides a baseline for evaluating your meter's suggestions and works when batteries die.
On a sunny day, set aperture to f/16 and shutter speed to 1/(ISO). For ISO 400 film on a sunny day: f/16 at 1/500.
Sunny 16 Variations
| Condition | Aperture | Description |
|---|---|---|
| Snow/Beach | f/22 | Bright sun + reflective surface |
| Sunny | f/16 | Sharp shadows |
| Slight overcast | f/11 | Soft shadows |
| Overcast | f/8 | No shadows |
| Heavy overcast | f/5.6 | Dark grey sky |
| Open shade | f/4 | Subject in shade, lit by sky |
How to use it: Before shooting, estimate what Sunny 16 would suggest. Compare to your meter. If they're wildly different, investigate why before shooting.
Meter Reading Technique
Getting good meter readings requires intention. Here's how to approach it:
1. Identify What Matters
Before metering, decide what exposure you want. Usually this means:
- Expose for shadows: In high contrast, ensure shadows have detail (negative film handles this well)
- Expose for skin: In portraits, skin should render correctly
- Expose for the subject: Whatever's important should be properly exposed
2. Take a Careful Reading
For centre-weighted meters:
- Fill the centre circle with your subject or a mid-tone area
- Take the reading
- Recompose if needed
For spot meters:
- Meter a specific tone you want to control
- Place that tone where you want it (middle grey, one stop over, etc.)
- This is the foundation of zone system thinking
3. Consider Compensation
Your meter suggests settings for middle grey. Adjust for:
| Subject | Compensation | Reason |
|---|---|---|
| Snow, white wall | +1.5 to +2 stops | Prevent grey rendering |
| Dark subject, shadows | -1 to -2 stops | Prevent washing out |
| Backlit subject | +1.5 to +2 stops | Expose for shadowed side |
| Sunset sky | -1 stop | Preserve colour saturation |
Working Without a Meter
Many classic cameras lack built-in meters (or have dead ones). Options:
Use Sunny 16
Estimate using the rule. With negative film's latitude, you'll get printable results. This works surprisingly well once you develop the skill.
Phone Light Meter Apps
Apps like Light Meter (iOS) or Photo Light Meter (Android) use your phone's camera as a reflective meter. Not lab-accurate but useful for verification.
Handheld Meter
A dedicated handheld meter (Sekonic, Gossen) offers incident metering and precise control. Essential for studio work, optional for general shooting.
The "Bracket and Learn" Method
- Estimate exposure
- Shoot at your estimate, then +1 stop, then -1 stop
- Review results
- Learn from the difference
After a few rolls, your estimates improve dramatically.
Exposure Latitude and Film Choice
Film choice affects how critical metering becomes:
Colour negative film (C-41): Very forgiving. Portra 400 handles +3/-1 stops easily. When in doubt, overexpose slightly — shadow detail is more recoverable than blown highlights.
Black & white negative: Also forgiving, typically +2/-2 stops printable. Shadows and highlights can both be recovered in printing or scanning.
Slide film (E-6): Unforgiving. Aim for ±0.5 stop accuracy. Slight underexposure is often preferable to overexposure (which clips highlights irreversibly).
With slide film, meter carefully and bias toward slight underexposure. Overexposed highlights cannot be recovered. Consider bracketing important shots.
Common Metering Situations
Backlit Subjects
The classic failure mode for reflective meters. The bright background fools the meter into underexposure.
Solutions:
- Get close and meter the subject only
- Use spot meter on subject
- Add +1.5 to +2 stops compensation
- Use fill flash
High Contrast Scenes
Scenes with both deep shadows and bright highlights exceed film's dynamic range. You must choose what to sacrifice.
For negative film: Expose for shadows, let highlights go. Shadow detail is more valuable than highlight detail in negatives.
For slide film: Expose for highlights, let shadows go. Blown highlights are worse than blocked shadows in slides.
Snow and Beaches
Bright, reflective surfaces fool meters into underexposure.
Solution: Add +1 to +2 stops compensation. The scene is genuinely bright — let it render bright.
Dark Subjects
A black cat against a dark background reads as underexposed. The meter tries to brighten it to middle grey.
Solution: Subtract -1 to -2 stops from the meter reading.
Summary
- Your camera meter assumes everything is middle grey — adjust for subjects that aren't
- Learn Sunny 16 as a backup and sanity check
- Centre-weighted metering is predictable; matrix metering is convenient but opaque
- With negative film, when in doubt, overexpose slightly
- Practice estimating exposure — it's a skill that improves with use
Metering becomes intuitive with practice. After a few hundred frames, you'll glance at a scene and know approximately what exposure it needs. The meter becomes verification, not revelation.