📸 Photography Exposure Value (EV) & Lux Calculator
Calculate photography Exposure Value (EV100), ambient scene illuminance in Lux, and aperture/shutter/ISO exposure triangle reciprocity settings.
Hazy sun, distinct shadows
Equivalent exposures — every one of these gives the same brightness
| Aperture | Exact shutter | Nearest click |
|---|---|---|
| f/1.4 | 1/8163 | 1/8000 |
| f/2 | 1/4000 | 1/4000 |
| f/2.8 | 1/2041 | 1/2000 |
| f/4 | 1/1000 | 1/1000 |
| f/5.6 | 1/510 | 1/500 |
| f/8 — yours | 1/250 | 1/250 |
| f/11 | 1/132 | 1/125 (+0.08 stop) |
| f/16 | 1/63 | 1/60 (+0.06 stop) |
| f/22 | 1/33 | 1/30 (+0.14 stop) |
| f/32 | 1/16 | 1/15 (+0.06 stop) |
They expose identically and look completely different. Opening up shortens the shutter and shrinks depth of field; stopping down lengthens it and lets movement blur. Choosing between rows in this table is most of what exposure decisions actually are.
EV = log₂(N² ÷ t), with ISO folded in as −log₂(S ÷ 100) to express the result at ISO 100. One EV is one stop, and one stop is a doubling of light. The lux figure uses the common calibration constant of 2.5 and is an approximation — meters from different makers use slightly different constants, so treat it as an order-of-magnitude reading rather than a photometric measurement.
What Photography Exposure Value (EV) & Lux Calculator Does
Exposure value is a single number describing how much light a combination of aperture and shutter speed lets through. Any two settings with the same EV expose identically, which is exactly why the number exists: it turns three interacting controls into one figure you can reason about.
EV is defined from the settings alone — log₂ of the aperture squared divided by the shutter time — and then quoted at ISO 100 by convention, so that the number describes the scene rather than your camera. Shooting the same settings at ISO 400 describes a scene two stops darker, which is why the ISO term subtracts.
The practical use is the equivalent-exposure table. At EV 14, f/8 and 1/250 give the same brightness as f/4 and 1/1000, or f/16 and 1/60. They expose identically and look nothing alike: wide apertures shorten the shutter and collapse depth of field, small ones lengthen it and let movement blur. Choosing between rows in that table is most of what an exposure decision actually is.
One thing worth knowing about the sunny 16 rule: f/16 at one over the ISO gives EV 14.64, not a clean 15. The rule is about a third of a stop generous, which was deliberate — slight overexposure was the safe direction on negative film.
How to Use Photography Exposure Value (EV) & Lux Calculator
- Select lens aperture (f-number), shutter speed, and ISO speed
- Review computed EV100 index and lighting scene classification
- Inspect estimated ambient scene illuminance in Lux
Formula Used by Photography Exposure Value (EV) & Lux Calculator
Exposure value, and the ISO correction
EV = log₂(N² ÷ t) · EV₁₀₀ = log₂(N² ÷ t) − log₂(S ÷ 100) · lux ≈ 2.5 × 2^EV₁₀₀
- N
- the f-number — f/8 means N = 8
- t
- shutter time in seconds, so 1/250 is 0.004
- S
- ISO sensitivity
- one EV
- one stop — a doubling or halving of light
Worked example
f/8 at 1/250, ISO 100.
- N² = 64; 1 ÷ t = 250; 64 × 250 = 16,000
- EV = log₂(16,000) = 13.97
- ISO is 100, so no correction
Result: EV 13.97 — hazy sunshine with distinct shadows, and about 40,000 lux.
What each EV looks like
At ISO 100. Every step is one stop, so a difference of 3 EV is eight times the light.
| EV₁₀₀ | Scene | Sunny-day equivalent |
|---|---|---|
| 16 | Snow or beach in bright sun | f/16 at 1/250 |
| 15 | Bright direct sun, distinct shadows | f/16 at 1/125 |
| 14 | Hazy sun, soft shadows | f/11 at 1/125 |
| 13 | Cloudy bright, or open shade | f/8 at 1/125 |
| 12 | Overcast, no shadows | f/5.6 at 1/125 |
| 10 | Heavy overcast, or sunset | f/2.8 at 1/125 |
| 7 | Bright indoor lighting | f/2 at 1/30 |
| 5 | Ordinary domestic interior at night | f/2 at 1/8 |
| 0 | Dim night scene, distant city lights | f/2 at 4 s |
| −4 | Moonlit landscape | f/2 at 60 s |
Equivalent exposures at EV 14
All identical in brightness, all different in look. Shutter speeds are the nearest standard click — at f/8 the exact value is 1/256.
| Aperture | Shutter | Effect |
|---|---|---|
| f/2.8 | 1/2000 | Very shallow depth of field, movement frozen |
| f/4 | 1/1000 | Shallow, still frozen |
| f/5.6 | 1/500 | Moderate |
| f/8 | 1/250 | The general-purpose default |
| f/11 | 1/125 | Deep focus, hand-holdable |
| f/16 | 1/60 | Deep focus, movement starts to blur |
How to Read Your Result
Pick the constraint first
Decide what the picture needs — a specific depth of field, or a shutter fast enough to freeze what is moving — and let the other setting follow. EV tells you what the other one has to be. Choosing both at once and hoping is how you get a picture that is neither sharp nor shallow.
ISO buys you a whole row, at a cost
Doubling ISO shifts every pairing one stop, which is what lets you shoot indoors at all. Modern sensors handle high ISO far better than film ever did, but noise still rises and dynamic range still falls, so it is the setting to move last rather than first.
Meters read reflectance, and get fooled
A camera meter assumes an average scene and will underexpose snow and overexpose a dark subject, because it is trying to make both mid-gray. Knowing the EV of the conditions is exactly how you catch that: if the meter disagrees with sunny 16 on an obviously sunny day, the meter is being misled.
The lux figure is an approximation
It uses the common calibration constant of 2.5. Meter manufacturers use slightly different constants, so treat it as an order of magnitude rather than a photometric measurement — useful for comparing conditions, not for specifying lighting.
Limitations & Accuracy Notes
- Assumes full-stop values. Real cameras work in half or third stops, and the table rounds to the nearest full-stop click.
- Ignores lens transmission. The f-number is a geometric ratio; T-stops account for actual light loss and can differ by a third of a stop or more.
- No reciprocity failure, which matters for film at very long exposures.
- Filters, bellows extension and teleconverters all cost light and are not modeled.
- The lux conversion depends on a calibration constant that is not standardized between manufacturers.
Frequently Asked Questions
What is Exposure Value (EV) in photography?
What does EV 15 represent?
What is exposure value?
What is a stop?
If the exposure is the same, does it matter which setting I change?
What is the Sunny 16 rule?
Does EV account for ISO?
Is anything sent to a server?
References & Further Reading
- Wikipedia — exposure value — The definition and the standard EV table for scene brightness