Equivalent Exposure Calculator
Change the aperture or the ISO and get the shutter speed that keeps the exposure exactly the same, with the stops shown.
Results
Shutter that keeps the exposure
0.000245
s
The same, as one over
4081.6
Exposure value at ISO 100
12.966
Stops the aperture gave
-3.029
Stops the ISO gave
2.000
Stops the shutter gave back
-5.029
Exposure value at that ISO
12.966
Scene luminance implied
1000.00
cd/m²
What this tool does
Aperture, shutter and ISO are three ways of spending the same budget: double one and you must halve another. This page does the arithmetic of that trade, and shows where each stop came from — so you can see that opening from f/8 to f/2.8 bought three stops, and that raising ISO 100 to 400 bought two more, and that the shutter has to give all five back.
Formula
EV = log₂(N² ÷ t) − log₂(S ÷ 100) · same exposure: N² ÷ (t S) stays constant · t₂ = t₁ (N₂ ÷ N₁)² (S₁ ÷ S₂)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
n1 | f-number you had | — |
t1 | Shutter you had | s |
s1 | ISO you had | — |
n2 | f-number you want | — |
s2 | ISO you want | — |
T2 | Shutter that keeps the exposure | s |
FR | The same, as one over | — |
EV | Exposure value at ISO 100 | — |
SA | Stops the aperture gave | — |
SI | Stops the ISO gave | — |
SS | Stops the shutter gave back | — |
EB | Exposure value at that ISO | — |
LV | Scene luminance implied | cd/m² |
Worked example
- f-number you had8
- Shutter you had0.008 s
- ISO you had100
- f-number you want2.8
- ISO you want400
- Shutter that keeps the exposure0.000245 s
- The same, as one over4081.6
- Exposure value at ISO 10012.966
- Stops the aperture gave-3.029
- Stops the ISO gave2.000
- Stops the shutter gave back-5.029
- Exposure value at that ISO12.966
- Scene luminance implied1000.00 cd/m²
Limitations
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.