Exposure calculator●
Keep the same exposure while you change aperture, shutter speed or ISO, or plan ND filters and star shots.
The result updates as you type. Nothing you enter leaves this page.
Enter settings that give a good exposure, then choose which setting to find.
Result
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Your numbers are used only in this browser tab. Nothing is sent, saved or tracked.
How exposure, ND filters and star shots work
Exposure is how much light reaches the sensor, and three settings control it. Aperture sets the size of the opening, shutter speed sets how long it stays open and ISO sets how much the signal is amplified. Each full stop doubles or halves the light, so f/2.8 at 1/250 s lets in the same light as f/4 at 1/125 s. This calculator keeps the exposure equal while you change one setting, then shows the nearest standard value and a table of equivalent pairs. ND filters darken the whole scene so you can use a longer shutter speed: a 10 stop filter multiplies the time by 1,024, which turns 1/125 s into about 8 seconds. For night sky photos, stars start to trail when the exposure is too long. The rule of 500 divides 500 by your full frame equivalent focal length. The NPF rule also uses the aperture and the pixel size, so it suits high resolution cameras better. Results are estimates, so check the image on screen and adjust.
Image resizer →Common questions
What is equivalent exposure?
It is a different combination of aperture, shutter speed and ISO that lets the same amount of light reach the sensor. Opening the aperture by one stop and halving the exposure time gives the same brightness.
How many stops is an ND filter?
ND8 is 3 stops, ND64 is 6 stops and ND1000 is about 10 stops. Each stop doubles the time you can expose for. An optical density of 0.3 equals one stop.
How do I use the rule of 500 for stars?
Divide 500 by your full frame equivalent focal length. A 24 mm lens on full frame gives about 21 seconds. The NPF rule is stricter on high resolution cameras because it also uses the aperture and the pixel size.
Why does the aperture change by a factor of 1.4?
Light depends on the area of the opening, so one stop is a factor of the square root of 2, about 1.4. That is why the scale reads f/2, f/2.8, f/4, f/5.6 and f/8.
What does the EV value mean?
EV is one number for scene brightness at a given setting. This tool shows it at ISO 100. A bright sunny day is about EV 15 and a dim room is about EV 5 to 7.
Can I type any aperture or shutter speed?
Yes. Use forms such as f/2.8, 2.8, 1/250, 0.5, 2s or 2m. The result is shown exactly and as the nearest standard setting.