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.

ISO of the starting exposure.

f/

f-number you want to shoot.

ISO for the new exposure; keep it equal to From ISO if only the aperture changes.

Results

Shutter to keep EV
0.016327s

New shutter that keeps the same brightness (EV100).

Shutter move
3.03stops

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

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

Example products

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Calculation method

Brightness is conserved when N² × 100/(t × ISO) stays constant, which is the same as holding EV100. 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. To fold the filter in here instead, multiply the To aperture by 2^(ND/2) — √2 per ND stop.

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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