Exposure Calculator
Trading ISO, aperture and shutter without losing the look you agreed on. The calculator above takes iso, aperture, shutter and target and returns equivalent settings and stop difference — computed in your browser, with no sign-up and nothing leaving your device.
Exposure Calculator
- New aperture
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- Difference
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Runs entirely in your browser — no sign-up, nothing transmitted.
What the number actually depends on
Doubling ISO from 800 to 1600, opening one stop from T2.8 to T2, and halving shutter from 1/50 to 1/100 are each worth exactly 1 stop — but only the aperture changes the image.
Most cinema sensors have a second native ISO, typically around 2500 to 3200; using it costs no extra noise, using the value 1/3 stop next to it does.
The gap between a number that goes into a quote and one that holds on the day is rarely the formula — it is whether the constraints were entered honestly. That is why the inputs are spelled out below.
Common mistakes
These come up most often in practice. They rarely break the maths; they routinely break the day:
- Fixing exposure with shutter angle and getting strobing pans
- Riding ISO past the second native value in a dark interior
In day-to-day production
Shutter angle is locked by motion rendering: at 25 fps the 180-degree rule fixes it at 1/50 s. It is the one variable of the 3 you should not trade for exposure.
The number belongs in production planning — the point where a decision is still free to change. Working it out on the shoot day is no longer calculating; it is finding out.
In TillyGen this is not a separate step: the result sits inside the plan itself, alongside the shot list, schedule and call sheet. Change a constraint and the dependent values move with it — the affected parts of the plan are flagged rather than quietly left behind.
Frequently asked
How accurate is the Exposure Calculator?
The maths is exact; the inputs rarely are. Treat the result as a solid floor and add your buffer deliberately rather than smuggling it into the inputs — a flattered input hides the buffer from everyone who plans with it later.
Is the calculator free?
No. It runs entirely in your browser, with no sign-up and nothing transmitted. There is no usage limit and no account.
Where does this fit in production planning?
In production planning. There it is a basis for deciding; later it is only a finding.
Can I export the result?
The calculator itself only displays the value. In TillyGen it lands directly in the shot list, schedule and call sheet, and goes out as PDF, CSV or through the API to everyone working from it.
What does the calculator return?
Equivalent settings and stop difference. The first value is the one you carry into the plan; the rest show how sensitively it reacts to the inputs.
What should I watch for in the result?
Mainly this: fixing exposure with shutter angle and getting strobing pans. That is the mistake that most often turns a correctly calculated number into one that does not hold.