Photography Calculators

Exposure & light

Exposure Shift Calculator

You liked f/2.8 at 1/500, ISO 100, but you need f/8 for DoF. This holds the photographic triangle: new shutter is old shutter scaled by the square of the aperture ratio and the ISO ratio. The stop delta is how far the shutter moved. Take a test shot — same EV is not the same motion blur.

Inputs

Units
f/

f-number you already metered or chimped.

s

1/500 is 0.002.

f/

f-number you want to shoot.

Results

Shutter to keep EV
0.016327s
Shutter move
3.03stops

Positive means the new shutter is longer (more time).

Recommended gear

Calculation method

Exposure is conserved when N²/t × 100/ISO stays constant. Solving for the new shutter: multiply the old time by the square of (new f-number over old f-number) and by (old ISO over new ISO). Opening the aperture shortens the shutter; raising ISO shortens it. Stop delta is log2 of new shutter over old shutter — how many stops the time axis moved.

Exact formula

t_to = t_from × (N_to/N_from)² × (ISO_from/ISO_to). stopDelta = log2(t_to/t_from). Limits: Same scene luminance; ND, flash and auto-ISO behaviour omitted.

Equivalent look vs equivalent EV

f/2.8 and f/8 at the same EV are the same brightness, not the same photograph. If you wanted the f/2.8 background, do not ‘compensate’ by stopping down.

Handheld limit

If the new shutter drops below 1/(focal × crop), you need IBIS, a tripod or more ISO. Check the handheld shutter calculator before you accept a 1/20 s ‘equivalent’.

Frequently asked questions

Why is stop delta not zero?

It is the shutter’s share of the compensation, not a leftover EV error. If you close three stops on the aperture and ISO stays put, shutter should lengthen three stops and delta reads +3.

What if I also add an ND?

Do this shift first, then multiply the new shutter by 2^ND on the ND calculator. Or add the ND stops into a second pass.

Flash in the mix?

Ambient follows this triangle. Flash does not — guide number and distance set flash EV. Dragging the shutter here brightens ambient only.

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