How Multiple Flash works

Summary

Calculator for technical and large-format work that combines multiple flash pops on the same frame. Aggregates per-pop distances and Guide Numbers into a single cumulative aperture.

How it works

Some technical and large-format work uses several flash pops on the same frame to either light a deep scene (paint with light) or to combine multiple flash heads at different distances. Each pop adds light, so the cumulative effect is more than any single pop alone. This modal works out the equivalent total exposure.

Number of pops

How many times the flash will fire on the same frame. From two up to eight pops in this modal. More pops mean more cumulative light and a smaller required aperture.

Per-pop distance

Enter the flash-to-subject distance for each pop. They can be different, which is the whole point: a far pop adds less light than a near one.

Guide Number

Same as the single-flash calculator. Make sure you are using the right GN for the ISO of your film.

Cumulative aperture

The output is the f-stop that gives a correct exposure when all the pops have been added together. Set that on the lens, then fire the pops without advancing the film.

Practical use

On a view camera in a dark interior, lock the shutter open on Bulb, then walk through the scene firing the flash at each area you want to light. Each pop is one entry in the modal.