Exposure Triangle Calculator
Find equivalent exposures by adjusting ISO, aperture, or shutter speed while maintaining the same overall exposure.
The exposure triangle is the foundation of every conscious exposure decision in photography. ISO, aperture, and shutter speed each affect the amount of light hitting the sensor, but each also has side effects: ISO adds noise, aperture controls depth of field, shutter speed controls motion blur. Understanding equivalent exposures lets you trade one variable for another while keeping the brightness constant.
Each full stop of change doubles or halves the light. Opening from f/4 to f/2.8 is one stop more light. Slowing from 1/250 to 1/125 is one stop more light. Raising ISO from 200 to 400 is one stop more light. These are interchangeable for exposure purposes, but not for creative effect.
The three variables and their tradeoffs
Shutter speed controls motion blur. Fast shutter (1/1000+) freezes motion. Slow shutter (below 1/60 handheld) introduces camera shake or intentional motion blur. For weddings and events, 1/200-1/500 is typically the minimum for sharp people shots. Aperture controls depth of field. Wide aperture (f/1.4-f/2.8) produces shallow depth of field, blurring backgrounds. Narrow aperture (f/8-f/16) brings more of the scene into focus. ISO controls sensor sensitivity and noise. Higher ISO lets you shoot in darker conditions but introduces digital grain. Modern cameras handle ISO 3200-6400 reasonably well; above 12800 noise becomes obtrusive on most sensors.
Exposure value (EV)
EV is a single number representing the combination of aperture and shutter speed at ISO 100. Each whole EV number represents a doubling or halving of exposure. EV 0 is 1 second at f/1.0, ISO 100. EV 15 is typical bright daylight. EV 5-8 covers indoor lighting situations. Knowing the EV of your shooting environment helps you quickly find combinations that will work before raising your camera.
Reciprocal exposures for weddings
In wedding photography, I shoot mostly in aperture priority or manual with auto-ISO. The goal is to maintain 1/200+ shutter for sharp people shots, f/2-2.8 for background separation, and let ISO float to match the light. In dark reception venues, ISO 3200-6400 at f/2.8 and 1/200 is a typical starting point. Running the equivalent exposure math in your head before stepping into a new lighting environment saves a lot of missed shots.
Frequently asked questions
What is the sunny 16 rule?
On a clear sunny day, set aperture to f/16, shutter to 1/ISO. At ISO 200, that is 1/200 at f/16. This produces a correct exposure in bright sunlight without a meter. It is a useful backup when your camera's meter is unreliable (highly reflective snow, backlit scenes) and a good mental reference point for understanding exposure in general.
What is the 500 rule for astrophotography?
Divide 500 by your focal length to find the maximum shutter speed before stars show trailing. At 24mm: 500/24 = 20 seconds maximum. At 50mm: 10 seconds maximum. For sharper stars (especially on high-resolution sensors), use the NPF rule, which also accounts for aperture and sensor resolution.