What Is This Calculator For?
This exposure calculator helps analog film photographers determine the correct exposure settings for their camera. It's designed to work with any manual camera. The calculator solves the fundamental relationship between aperture, shutter speed, ISO, and exposure value (EV).
How Does It Work?
The calculator uses the exposure triangle relationship where three values determine the fourth:
- Exposure Value (EV) - Represents the amount of light in a scene
- Aperture (f-stop) - Controls how much light enters through the lens
- ISO - The film's sensitivity to light
- Exposure Time - How long the shutter stays open
Simply provide any three values, and the calculator will compute the fourth. The dropdowns for light situations and shutter speeds make it practical for real-world shooting scenarios.
Practical Use Cases
- Metering Without a Light Meter: Know the lighting situation (sunny day) and your film ISO, calculate what aperture/shutter combo to use
- Planning Your Shot: Want to shoot at f/2.8 with ISO 400 film? Find out what shutter speed you'll need for different lighting
- Reciprocity: Calculate equivalent exposures - if you know one combination works, find alternatives with different aperture or shutter speed
- Flash Photography: The 1/50s flash sync speed is clearly marked to help you calculate proper aperture for flash shots
- Learning Exposure: Understand the mathematical relationships between all exposure variables
Understanding the Formulas
Master Formula: Calculating EV
This is the complete photography exposure formula that relates all four exposure variables: Exposure Value (EV), Aperture (A), ISO film speed, and Time (T). The constant 100 is a calibration factor based on light meter standards.
Calculating Aperture
Rearranged from the master formula to solve for aperture. Given a lighting situation (EV), your film speed (ISO), and desired shutter speed (T), this tells you which f-stop to use.
Calculating ISO
Rearranged from the master formula to solve for ISO. This is useful for determining what film speed you need for specific lighting conditions, aperture, and shutter speed combinations. For example, if you want to shoot at f/2.8 and 1/1000s in bright sunlight (EV 15), you can calculate the required ISO.
Calculating Exposure Time
The most common calculation - given your lighting conditions (EV), film speed (ISO), and chosen aperture (A), this tells you what shutter speed to set on your camera.
About Analog Camera Shutter Speeds
The shutter speed dropdown includes common mechanical speeds available on analog cameras (1s to 1/1000s). The 1/50s flash sync speed is specially marked because it's a common flash sync speed for many cameras. Using faster speeds may result in partial frame exposure on some cameras (the shutter curtain will appear in your photo).
Full Stops vs. Half Stops
Aperture values are marked with indicators:
- ● Full stops (f/1.0, f/1.4, f/2.0, f/2.8, etc.) - Each full stop doubles or halves the light
- ◐ Half stops (f/1.2, f/1.7, f/2.4, etc.) - Intermediate values for finer exposure control
Moving one full stop changes exposure by exactly 2× (one "stop" of light). Half stops provide intermediate adjustments of approximately 1.4×.
Tips for Using This Calculator
- Start with the Light Situation dropdown if you're outdoors - it's often easier to identify "sunny day" than to know the exact EV number
- The Sunny 16 Rule is built in: EV 14 (sunny day) + ISO 400 + f/16 = 1/400s (close to 1/500s)
- Use the Shutter Speed dropdown when inputting time - it ensures you select speeds that actually exist on your camera
- Remember that calculated apertures might not exactly match standard stops - the calculator will suggest the closest available aperture
- The displayed values are precise, but in practice you'll use the closest available setting on your camera