Exposing a scene
Exposure is about controlling how much light reaches your film. You balance three settings—ISO, shutter speed, and aperture—to get a well-lit image. This guide covers the exposure triangle, how cameras measure light, and a backup method when meters fail.
The exposure triangle
Three settings work together to control brightness:
- ISO – How sensitive the film is to light
- Shutter speed – How long the film is exposed
- Aperture – The size of the lens opening
Changing one affects the others. Get all three balanced and you get a correctly exposed image.
ISO
(If you're unsure what ISO means, see Choosing and loading film.)
Once you've loaded your film, the ISO is fixed. You can push or pull the entire roll during development to adjust exposure afterward.
Setting ISO on your camera
Manual dial (SLRs & rangefinders) – Find the ISO dial near the rewind crank or shutter speed dial, lift it, and rotate to match your film
DX-coded (most point & shoots) – The camera reads the film canister automatically. No setting needed
Fully manual (older cameras) – No ISO dial. You'll adjust shutter speed and aperture based on your film's rated ISO
Shutter speed
Shutter speed controls how long the film is exposed.
| Speed | Effect | Use for |
|---|---|---|
| Fast (1/500s, 1/1000s) | Freezes motion | Sports, wildlife |
| Medium (1/125s, 1/250s) | Freezes some motion | General photography, slow or stationary subjects |
| Slow (1/30s, 1s) | Adds blur | Light trails, creative effects |
| Bulb (B) | Stays open while you hold it | Long exposures, night photography |
TIP
Slower shutter speeds (1/30s or slower) cause blurry photos from camera shake when handheld. Use a tripod or brace yourself against something solid.
The dial usually shows only the denominator—"500" means 1/500th of a second.
Setting shutter speed
Manual dial – Turn to select your speed (e.g., 1/125s, 1/250s)
Auto mode – The camera picks for you
Aperture priority (A/Av) – You set aperture; camera sets shutter speed
Aperture
Aperture controls the size of the lens opening. It's measured in f-stops.
- Lower f-number (e.g., f/1.8) = wider opening = more light = blurry background
- Higher f-number (e.g., f/16) = narrower opening = less light = sharper background
TIP
Very small apertures (f/22, f/32) can cause diffraction, reducing sharpness.
Setting aperture
Manual lens ring – Rotate to your desired f-stop
Auto or priority modes – The camera may adjust automatically, or you set it and let the camera handle the rest
Metering in camera
Your camera measures light to suggest exposure settings. Most built after the 1960s have a light meter inside.
Metering modes
| Mode | What you set | What camera sets |
|---|---|---|
| Program (P) | Nothing | Aperture + shutter |
| Shutter priority (S/Tv) | Shutter speed | Aperture |
| Aperture priority (A/Av) | Aperture | Shutter speed |
| Manual (M) | Both | Nothing |
For learning, start with Manual or Aperture priority so you understand how each setting affects the image.
Reading the meter
Different cameras display readings differently:
- Needle meters – Move the needle until it aligns with a centre mark
- LED/LCD meters – Look for a + or − indicator; adjust until exposure is balanced
- Fully automatic – May just fire or warn if it can't find a good exposure
External meters
For more accuracy, especially in tricky lighting:
- Professional meters – Measure incident light (light falling on your subject) for precision
- Smartphone apps – Less accurate but convenient and more adjustable than built-in meters
Metering by eye
When you have no meter, use the Sunny 16 Rule:
- Set aperture to f/16 on sunny days
- Set shutter speed to match your ISO (ISO 100 → 1/100s)
| Condition | Aperture |
|---|---|
| Bright sun | f/16 |
| Slight overcast | f/11 |
| Overcast | f/8 |
| Heavy overcast | f/5.6 |
| Deep shade | f/4 |
Use this as a starting point—check your results and adjust from there.