209 exposure cells — f/11 is really 11.314 and 1/60 s is really 1/64 s
The exposure scale is geometric — each step doubles the light — but the dial is engraved with rounded, readable numbers. So the EV comes out as a whole number when you add the two scale positions, and drifts by up to 0.174 when you feed the engraved numbers into the logarithm. All 209 cells (eleven apertures × nineteen shutter speeds) carry both values.
EV (by stops)
Aperture \ Shutter · ISO 100
| 1/8000 | 1/4000 | 1/2000 | 1/1000 | 1/500 | 1/250 | 1/125 | 1/60 | 1/30 | 1/15 | 1/8 | 1/4 | 1/2 | 1" | 2" | 4" | 8" | 15" | 30" | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| f/1 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | -1 | -2 | -3 | -4 | -5 |
| f/1.4 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | -1 | -2 | -3 | -4 |
| f/2 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | -1 | -2 | -3 |
| f/2.8 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | -1 | -2 |
| f/4 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | -1 |
| f/5.6 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| f/8 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
| f/11 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 |
| f/16 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 |
| f/22 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 |
| f/32 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 |
The scale is engraved rounded
Apertures step by √2, so the true values are 1, 1.414, 2, 2.828, 4, 5.657, 8, 11.314, 16, 22.627, 32. The dial is engraved 1.4, 2.8, 5.6, 11, 22. Shutter speeds step by 2, so 1/64, 1/128, 1/256 s are the true values, engraved as 1/60, 1/125, 1/250. f/11 and f/22 are shaved the most (−0.081 stop), the 1/60–1/30–1/15 family next (−0.093 stop). Where those two meet — six cells — the drift reaches 0.174, about a sixth of a stop. Invisible in a photograph, but it is why two exposure calculators can disagree.
The equal-EV diagonal
Close the aperture one stop and slow the shutter one stop and the EV does not move. So the cells of equal EV lie along a diagonal. The longest such run is eleven cells; runs get shorter toward the corners of the table.
Same EV, different photograph
Cells on the same diagonal put the same amount of light on the film or sensor. The photographs still differ: a wider aperture blurs the background, a slower shutter blurs whatever moves. Only the brightness matches.
The Sunny 16 rule
On a bright sunny day, set f/16 and the shutter to one over the ISO. At ISO 100 that is 1/100 s, which is not on the dial, so you use 1/125 s — in this table f/16 · 1/125 is EV 15, and EV 15 is bright sun. Still useful when you have no meter.
Raising the ISO
ISO doubles by the stop as well, so doubling it raises the EV by one: the same aperture and shutter now cover a scene one stop darker.
How to read it
- EV = log2(aperture² ÷ exposure time). f/1.0 for one second is EV 0.
- Because the scale doubles each step, the EV equals the sum of the two scale positions.
- Close the aperture one stop and the EV rises by one; speed up the shutter one stop and it rises by one.
- Cells of equal EV lie on a diagonal — combinations that pass the same amount of light.
- Doubling the ISO raises the EV by one.
- The engraved numbers are rounded, so computing from them drifts the EV by up to 0.174.
Common questions
Q. What does EV measure?
It puts the amount of light set by aperture and shutter together into one number: EV = log2(aperture² ÷ exposure time), with f/1.0 for one second as zero. Each step up halves the light.
Q. Why is the aperture squared?
The f-number is the focal length divided by the diameter of the opening, so a larger number means a smaller hole. The light admitted follows the area, which goes with the square of the diameter — hence the square of the f-number, inverted.
Q. Why does f/11 come before f/16?
Because the scale steps by √2. Eight times √2 is 11.314, engraved as 11, and 11.314 × √2 is 16. Only the 11 looks out of place.
Q. Can I estimate exposure without a meter?
Bright sun is about EV 15, cloudy 13, open shade 10, a bright interior 7. The Sunny 16 rule — f/16 with the shutter at one over the ISO — falls straight out of that.