The math the dials are hiding
Every exposure is a light budget. Aperture area, shutter time and sensor gain each contribute stops, and a stop is always the same thing: double or half the light. When your camera clicks from f/2.8 to f/3.2 it moved one third of a stop; from 1/125 to 1/250 it moved a full stop. Because everything is stops, any exposure can be rebuilt: give away a stop on one dial, take it back on another, and the histogram doesn't move.
This instrument does that bookkeeping in third stops — the same increments as your camera — so the answer it gives is a setting that actually exists on your dial, not a rounded approximation.
Field recipes working photographers actually use
- Freeze the first dance — metered f/1.8, 1/60, ISO 1600 but faces blur? Ask for 1/250 and let the instrument raise the ISO. Grain is fixable; blur is forever.
- Group shot depth — metered at f/2 but need f/5.6 for three rows of family? That's three stops — see exactly where they come from before you commit.
- Silky water — need 1/4s on a bright day? The instrument shows the aperture/ISO combination it demands, and whether it exists without an ND filter.
Learn the levers, then trust the meter
EV numbers make light tangible: full sun is EV 15, and every scene below it is a countable number of stops away. Photographers who internalize a few anchors — Sunny 16, overcast 12, dim hall 5 — walk into rooms already knowing roughly what the meter will say. Until then, the reference plate on this page is your cheat sheet; planning an outdoor session? Check when the good light lands with the golden hour instrument.
Questions from the bench
What is the exposure triangle?
The relationship between aperture, shutter speed and ISO. Each is measured in stops; one stop doubles or halves the light. Any exposure can be rebuilt with different combinations of the three — trade a wider aperture for a faster shutter, or higher ISO for less light on the sensor.
What is a stop?
A doubling or halving of light. f/2.8 → f/4 is one stop less light; 1/125s → 1/250s is one stop less; ISO 400 → 800 is one stop more sensitivity. Cameras adjust in third-stop clicks: three clicks equal one full stop.
What is EV (Exposure Value)?
A single number describing a light level, defined at ISO 100. Bright sun is about EV 15, an overcast day EV 12, a dim interior EV 5-7, a moonlit scene around EV -2. Two settings combinations with the same EV admit the same total exposure.
When should I trade shutter speed for ISO?
When motion blur threatens the shot. A safe handheld shutter is roughly 1/focal-length (with stabilization, slower). If people are moving, 1/250s or faster keeps them crisp — raising ISO one or two stops is nearly always better than a blurred moment.
Does this replace metering?
No — your camera meters the scene. This instrument answers the follow-up question: "I metered f/2.8, 1/60, ISO 1600 but I need 1/250 — what ISO do I need?" It keeps the exposure identical while you rearrange the triangle.