f/22 · 4 s — EV 7

The scale is engraved rounded

The engraved numbers give 6.92, a drift of -0.081 — -0.081 from the aperture and 0 from the shutter.

Other combinations at this EV

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.

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.

• ISO 50EV 6
• ISO 100EV 7
• ISO 200EV 8
• ISO 400EV 9
• ISO 800EV 10
• ISO 1600EV 11
• ISO 3200EV 12
• ISO 6400EV 13

Same aperture

Same shutter speed

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.

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.

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.