Exposure Triangle Solver

How to Read This Result

Pick which two settings you want to hold fixed relative to each other, choose your two starting values plus a starting value for the third, then choose what you're changing that third setting to. The tool returns the new value for the setting you locked, computed so the total exposure — the total amount of light reaching the sensor, in stops — stays identical to your starting point.

A stop is a doubling or halving of light. Every step up in ISO's standard sequence (100, 200, 400...) doubles sensitivity; every full stop down in aperture (f/2.8 to f/4, for example) halves the light passing through the lens; every halving of shutter time (1/125 to 1/250) halves the light reaching the sensor in that exposure. Because all three variables are measured in the same currency, any change in one can be exactly offset by a change in either of the other two, which is the entire premise of this tool.

Why 'Equivalent Exposure' Doesn't Mean 'Identical Photo'

Two settings combinations that produce the same total exposure will produce photos with the same overall brightness, but not the same look. Changing aperture changes depth of field; changing shutter speed changes motion blur and camera-shake risk; changing ISO changes noise. "Equivalent exposure" answers the brightness question only — you still have to decide which of the three variables you're willing to trade away for the effect you actually want.

ND Filters and Reciprocity

An ND filter reduces the light reaching the sensor by a stated number of stops, which lengthens the shutter speed needed for the same exposure by a factor of two per stop — an ND filter rated at 10 stops (often labeled ND1000) turns a 1/250 exposure into roughly 4 seconds. For very long film exposures, reciprocity failure means the film's effective sensitivity drops at extended exposure times, so the metered exposure needs to be lengthened further using a stock-specific correction — digital sensors don't suffer from reciprocity failure in the same way, so this correction only applies to film work.

A Worked Example

Say your meter reads a correct exposure at f/8, 1/250, ISO 100 for a daytime scene, but you want a long-exposure water-blur effect that needs several seconds of shutter time instead. Lock aperture and ISO, dial the shutter speed change into the tool, and it returns the aperture change needed to compensate — except in this case the aperture alone can't cover a jump from 1/250 to several seconds; that's exactly the situation an ND filter is built for, adding the missing stops of light reduction so the long shutter speed doesn't massively overexpose the frame. This is precisely the gap between exposure math and gear: the calculator tells you what's needed, but a physical filter is what actually gets you there.