Equivalent exposure calculator
Find a shutter duration that gives a conventional equivalent-brightness starting point after aperture or ISO changes. This tool does not meter the scene or predict sharpness.
Read shutter duration correctly
The input uses seconds. Enter 0.008 for 1/125 second or 2 for a two-second exposure. Entering 125 would mean 125 seconds, a completely different duration.
Check the relationship
Keeping ISO fixed and changing f/4 to f/8 requires four times the exposure duration for the conventional equivalent-brightness starting point. Starting at 0.008 second gives 0.032 second, about 1/31.25. Raising ISO from 100 to 200 halves that duration.
What the result cannot tell you
The calculator assumes stable scene light and idealized setting relationships. It does not account for lens transmission, filter factors, flash timing or manufacturer-specific ISO behavior. Check your meter, histogram and subject detail. ISO changes do not create additional light at the sensor.
Keep the result useful
Read the related guides for the reasons behind each decision. Inputs and results are processed on your device. This page does not send your entries to an external calculation service.
Read the detailed guides ↗