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Exposure Calculator

Enter the aperture, shutter speed and ISO that give a good exposure, then change one and see what the others must become to keep the same exposure, the exposure value of your settings, and the shutter speed behind an ND filter.

Your current settings

Exposure value (EV) of these settings
15.0
Light level they suit (EV at ISO 100)
15.0

Same exposure, different settings

New shutter speed
1/500 s

f/8, 1/500 s, ISO 100 gives the same exposure.

ND filter shutter speed

Filter strength as

Starts from your current shutter speed, 1/125 s

Shutter speed with the filter
8 s
Stops of light cut
10.0

How to use the exposure calculator

  1. Set the aperture, shutter speed and ISO of an exposure you're happy with (from your meter or a test shot).
  2. Under "Same exposure, different settings", choose the setting you want to change and its new value, and which setting should adjust to match.
  3. For long exposures, choose your ND filter to see the new shutter speed.

Worked example

A landscape meters at f/16, 1/125 s, ISO 100: EV 15.0. To blur the background you want f/8, two stops wider, so the shutter must be two stops faster: 1/500 s. Later you add an ND1000 filter for a long exposure of a waterfall: 1/125 s × 1000 = 8 seconds. An ND32000 on a 1/60 s exposure gives 8 min 53 s.

Formulas

  • EV = log₂(N² ÷ t); EV at ISO 100 = EV − log₂(ISO ÷ 100)
  • Same exposure when N² ÷ (t × ISO) stays the same
  • ND filter: stops = log₂(factor) or density ÷ 0.30103; new time = t × 2^stops

Settings are snapped to the third stops most cameras use. Everything runs in your browser.

Frequently asked questions

What is an equivalent exposure?

A different combination of aperture, shutter speed and ISO that lets in the same total exposure. Each full stop wider on the aperture can be balanced by a shutter speed twice as fast or an ISO half as high. f/16 at 1/125 s and f/8 at 1/500 s, both at ISO 100, give the same exposure; the second freezes motion better and has less depth of field.

What is EV (exposure value)?

A single number for a combination of aperture and shutter speed: EV = log₂(N² ÷ t). f/16 at 1/125 s is EV 15, as is f/8 at 1/500 s. Each step of 1 EV is one stop. The calculator also shows the light level your settings suit as EV at ISO 100, which is how light meters and exposure tables describe a scene.

How do I calculate shutter speed with an ND filter?

Multiply the shutter speed without the filter by the filter's factor: an ND8 (3 stops) turns 1/125 s into about 1/15 s, and an ND1000 (about 10 stops) turns it into 8 seconds. Filters marked by optical density cut 1 stop for every 0.3: a 0.9 filter is 3 stops, a 3.0 filter 10 stops.

Why does the calculator suggest a slightly different setting?

The exact answer often falls between the settings cameras offer, which come in third stops (1/125, 1/160, 1/200…; f/5.6, f/6.3, f/7.1…). The calculator shows the exact value and the nearest camera setting, with how far off it is in stops. A third of a stop is rarely visible, especially in raw files.

What is the Sunny 16 rule?

A way to expose without a meter: in bright sun, use f/16 with a shutter speed of 1 over the ISO (1/100 s at ISO 100). That's about EV 15 at ISO 100. Use the equivalent exposure section to turn it into a wider aperture or a faster shutter.

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