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EV - Exposure Value (photography)

An EV Calculator is just below.

Three EV Charts start near page bottom below.

An Exposure calculator to compare EV value and stops difference for any two camera or meter exposures is on the previous page.


There are concepts of relative EV adjustments, or of absolute EV values.

Relative EV

One major use of EV (Exposure Value) is just to measure any change of exposure, where one EV implies a change of one stop of exposure. Like when we compensate our picture in the camera. If the picture comes out too dark, our manual exposure could correct the next one by directly adjusting one of the three exposure controls (f/stop, shutter speed, or ISO). Or if using camera automation, the camera meter is controlling it, but we might apply +1 EV exposure compensation (or +1 EV flash compensation) to make the result goal brighter, as desired. This use of 1 EV is just another way to say one stop of exposure change.

Why not just say "stop"? I don't know, I suppose only two characters is easier to mark in the camera controls. In film days, both lens aperture and shutter speed dial had mechanical click stops, but ISO was another roll of film. But we still had to tell the camera metering system which ISO, and that ISO dial had click stops.

But regardless, one stop is an exposure factor of 2 (2x or 1/2). One EV is a step of one stops compensation value (could be aperture, shutter speed, or ISO, or some combination). This +1 EV means a one stop greater exposure. I assume this basic compensation use is already known. The rest of the page is about the absolute EV numbers.

There is one ambiguity involved with EV.

A light meter reads a higher EV reading to mean a brighter light requiring less exposure. In the EV Chart at bottom of this page, the highest EV numbers use the shortest exposures. Bright meters higher EV, and dim meters less EV. That is an Absolute EV number.

Our camera offers Compensation to correct exposures. Plus EV means add more exposure for dimmer light. Minus EV means use less exposure for brighter light.

The metered EV is what we actually have, more means brighter. Compensation is the correction about what we actually need, more means use more to make it brighter. This is a Relative EV number.

Absolute EV

EV is named Exposure Value, which sounds like an "exposure", but the EV chart does not measure light. The EV chart (below) is simply about camera settings, combinations of numerical camera settings of shutter speed and f/stop, which an equal EV number would be a set of equivalent exposures, regardless if it is a proper or accurate exposure or not. But a light meter could measure the light, and tell us EV at some ISO, then we look up the Settings in the EV chart for proper exposure at that ISO. EV basically gives a name to the group of several "equivalent exposure" choices in any one row of the EV chart below. Each row is a one stop step from its adjacent rows. A 1 EV step is one stop. This one stop step could be due to a light change, or an ISO change. When the camera compensation changes the camera settings by one stop, it calls it one EV. But the main concept is that this chart row of settings contains "equivalent exposure settings", labeled EV.

From Wikipedia:

N is f/stop Number, t is shutter speed (duration Time). The idea is that settings with a constant EV ratio are the same Equivalent Exposure. And that 1 EV is a 2x exposure difference. This typically confuses us, only because we have higher expectations. It is named Exposure Value, and it is very important to our exposure methods, but it's only about how exposure changes, it is not an exposure. Exposure needs ISO, which is not a factor of EV.

The basis of this is 2EV = N2/t   So EV is an exponent power of two. Stops of shutter speed reduce exposure in powers of two. F/stops are numbered incrementing by the square root of 2, then each squared number is a power of two. So what the EV formula is saying is that the EV increments in steps of 2x. It is about how exposure changes, not about any absolute light level. We also need ISO for that. But once related to a proper exposure with ISO, EV can become a meaningful absolute number of exposure.

A greater EV number meters a brighter light, so less Exposure is needed. A greater EV number is a lower row in the EV chart with faster shutter speeds, which is less Exposure. EV number is about the necessary camera settings, and EV number increases in the opposite direction from the Exposure required (one EV is same amount as one stop, both are a 2x change in exposure).


Below is a meter metering EV exposure in bright sun: The incident meter meters the light (aimed at the light instead of at the subject), and then uses the LV formula to convert EV to whatever ISO that we specified. Sekonic pictures are shown for the concept, which also makes the point that EV certainly varies with ISO. Bright direct sun will be near EV 15 at ISO 100. EV 15 in bright sun is very near Sunny 16. (This is Texas, 3 PM in mid-February, very clear sky. Note that days and skies can vary slightly, a previous clear day try was 0.2 EV lower). EV mode reads in tenths.


ISO 100 EV 15

ISO 800 EV 18

This is an example showing how the one standard EV Chart is good for any ISO. There is one standard EV chart (for full stops). The settings are already factored into the EV number.

On the EV 15 row in the EV chart below, you can find the settings f/16 1/125, which tells you those settings are EV 15 (for the ISO 100 specified). But if you look on the EV 18 row (on this same standard chart), you find f/16 1/1000 second, which is +3 EV, which row is correct exposures for EV 18 (for the ISO 800 specified). So for whatever ISO it may represent, just look up the EV on the EV chart. Or look up the settings to find the EV (for the ISO that causes those settings). That is why it is the standard chart. The Formula computes the standard chart for any use. We don't say "independent of ISO", because ISO has already influenced the situation, either the meters EV reading, or the camera settings selected.

Bright direct sunlight is normally very near EV 15 at ISO 100, or near EV 18 at ISO 800. In both cases, a light meter set to that ISO will read that EV value. The metered EV 15 row will show the correct settings for ISO 100, and the metered EV 18 row will be correct for ISO 800. On this one standard EV chart.

Any one row of the EV chart shows the Equivalent Exposures at THAT EV.

Used like this:

We can meter our bright sun scene as EV 15 at ISO 100, and look up EV 15 in EV chart, to see f/16 at 1/125 second settings to be used for exposure at ISO 100.

Or we can meter EV 18 at ISO 800, and look up EV 18 in EV chart, to see f/16 at 1/1000 second settings to be used for exposure at ISO 800.

Either setting would be the proper metered exposure at the ISO specified. Any of the Equivalent Exposures on the same row of the EV chart are the same exposure too. Anyway, ISO 800 meters 3 EV higher than ISO 100, and the camera exposure will require settings 3 EV higher too.

Sekonic calls it EV mode, but it computes exposure as the LV value from the formula below. Meters for photography don't show the "light value" of the scene, they show the EV of the camera settings we should properly use at a specified ISO (for that scene).

Or, the light meter's regular mode will indicate camera f/stop and shutter speed settings directly at the specified ISO, which combination of settings is found on only one row of the EV chart. The meter basically can do the EV chart lookup for us. So absolute EV is not a concept we really need for photography now, but it is still valid, and the rest of this page should help to explore the numbers.

When no light meter is available, the Sunny 16 method on next page offers approximations for several outdoor daytime situations.

EV Calculator

Full stops are Green. Third stops are Blue. Half stops are Red.

Calculate EV

Shutter speed

f/stop

ISO


If for a New ISO

EV charts normally only show only full stops for EV and settings. Any third stop is only a third stop from a full stop, so normally we can mange that offset in our head. However, EV charts for third stops and half stops have been provided below.

In bright sun, the photo above shows ISO 800 was metered as EV 18. And the EV chart shows f/16 at 1/1000 second is EV 18, so that works if using ISO 800. And if we compute EV of those settings, we get EV 18.
But ISO 100 metered EV 15, which is a different row in the EV chart, and of course, different settings of f/16 at 1/125 there, which also work if using ISO 100. These different settings will compute that EV 15, which due to ISO, is an Equivalent Exposure. ISO determines proper exposures for the settings, so to speak, and exposure cannot use the same settings at different ISO. So it's just different situations. Different light brightness does meter different EV values, requiring different settings. Then simply look up the proper settings on the correct EV row. Only one chart EV row has Equivalent Settings for that EV.


Some Wrong stories we hear (at least which need some elaboration)

Is ISO a factor of EV?   Of course it is. To have any meaning, certainly it is. The question only arises because, maybe at first glance, no ISO term appears in the EV formula. Maybe OK for math, but photographer's usage needs more understanding. The EV number chosen certainly depends on the shutter speed and f/stop settings. Some do make that stand that "EV is independent of ISO" (which is far too simplistic). The formula and the chart may seemingly be independent of ISO, however the concept of exposure is definitely about the ISO that you are using. The camera settings being computed were selected or metered for some specific ISO value. If it is to serve any useful purpose, obviously EV represents the camera settings to use at some specific ISO (the ISO we're using when we meter a correct exposure.) A different ISO will require different camera settings. This all works out fine.

So, exposure of the photo obviously depends on all three factors, aperture, shutter speed, and ISO. See Google for Exposure Triangle for more basics of that, which is about the very first concept photographers need to know about Exposure. Then knowing "photography" includes knowing when and why and how you give preference to each of those three parameters.

EV is named Exposure Value. It is the exposure of the camera settings at some ISO, and is assumed to be a proper exposure. But in the absolute sense (the EV chart), EV technically does just compute aperture and shutter speed, but it computes with those values that were selected for the specific ISO you are using. EV is certainly about some specific ISO situation. ISO is a factor that will obviously affect which f/stop and shutter speed values you select to properly expose your photo. Just saying "EV 16" has no meaning (other than to describe shutter and aperture equivalent settings). We instead might say "EV 16 at ISO 200", which then defines a useful exposure setting.

In the absolute sense, EV needs a defined ISO situation.

In the relative sense, EV is just a relative change in any of these three variables, one "stop" of exposure.

The EV nomenclature was invented to aid development and control of the first light meters placed into cameras in the late 1950s, back when film speed depended only on the roll of film loaded in the camera. EV camera "settings" are in that context, meaning shutter speed and aperture, for the film speed that was already defined and in place (for whatever ISO we are using). The old mechanical cameras only had settings for shutter speed and f/stop. However, in use, we still had to set a film ISO value for the meter, so we can meter an EV value at that ISO, and the camera settings are computed from EV (or the EV chart does this too). EV computes only the shutter and aperture settings (for that ISO), and when we use it, we see that EV cannot work without ISO. In use today, we set our light meter for ISO, and it tells us EV (or f/stop and shutter speed directly).

The EV formula may have no ISO term, but EV is of course computed from the camera settings which are already explicitly chosen to match some ISO to some scene light level for proper exposure - so EV of course depends on the ISO used. Digital cameras make it easier to change the media sensitivity, but concept is still the same. Change ISO and the EV changes (different settings are required). For a proper exposure of any scenes light level, any EV number applies to only the one ISO value metered (other ISO obviously have other EV, and other settings).

The camera settings (shutter speed and aperture) determine the cameras exposure of the light. ISO matches the camera settings to the scene light level, which is our goal. Considerations of depth of field or of stopping motion can choose other Equivalent Exposure setting choices (those on same row of EV chart), but the EV number still needs to come out right, for the ISO used. See the pictures below, the EV metered absolutely will depend on the ISO. Set the shutter and aperture to that EV, and the exposure will be correct.

This is not semantics, it is impossible to ignore that a different ISO will result in a different EV value (speaking of any real exposure). EV is the numerical combination of shutter speed and aperture settings in the camera, which choice was of course selected because of the ISO used. The EV chart is about the f/stop and shutter setting numbers for proper exposure, which certainly includes consideration of ISO. ISO has been accounted for in the settings that compute EV. Doubling ISO certainly will move us down one row in the EV chart, which is different settings, and a higher EV. EV involves whatever ISO we are using. ISO makes the EV settings correct for some specific level of light. And we certainly do get wrong exposure calculations if we try to factor in ISO a second time.

If in bright sun at ISO 100, the camera shutter speed and f/stop settings are any combination of Equivalent Exposure of 1/125 second f/16 (the row of the EV chart, see below), then these camera settings are EV 15 (that chart row where 1/125 sec at f/16 appears).

In the same bright sun, if a light meter at ISO 800 meters EV 18, then your correct exposure at ISO 800 is on the EV 18 row of the EV chart (Equivalent Exposures are on that row). EV has a value at any ISO, specifically the ISO we are using, in bright sun or in a dark room.

In these cases, then both EV 15 (at ISO 100) and EV 18 (at ISO 800) are the correct exposure. Equivalent exposures.

Hand-held incident light meters often do have a mode to meter an EV value (representing a row of equivalent settings in the chart), as an exposure for the ISO value you select. This could also be used for comparing brightness for non-photographic purposes, like lighting in work areas or plant growing areas. We have come to assume bright sun will meter EV 15 at ISO 100, if we set our light meter and camera to ISO 100.

But today, it is more usual for the light meter to have a mode to directly report the f/stop and shutter speed values to us, instead of a EV value. Those setting will be in the EV chart on only ONE row, so that EV value of that row agrees with metered value at the ISO value used. The meter looks up those settings for us, from the EV value.

The EV chart itself is Not about ISO. Or rather, it is about all ISO, any ISO. It is about camera settings for a proper exposure at whatever ISO. Different ISO values in the meter will meter different EV values (meaning, different combinations of shutter speed and aperture which match that ISO). ISO 400 will meter 2 EV higher than ISO 100 (so we move down two rows in the chart). The EV value is simply the combinations of the equivalent numerical camera settings. The meter is simply measuring luminance at some ISO, and then calling it EV. (but EV alone, without an ISO, is NOT a Light Value).

Sekonic has a conversion chart, of EV, Lux, foot candles, assuming ISO 100. We often do assume ISO 100, but EV does not necessarily mean ISO 100, except when we say that is what we mean.

Formulas

EV = log2 (fstop² / shutter time),   Exposure Value, the exposure effect of the camera settings used. The camera settings of f/1 at 1 second is EV 0, regardless of ISO. However, matching those camera settings to the scene light level makes ISO also be pretty important. So I'm saying it two ways. EV is independent of ISO in the formula, however the camera settings we choose to put into the formula definitely depend on ISO. EV is Not the light level, it is the camera settings we choose, which choice is influenced by ISO.

Mathematically, the EV values are exact only if computed with the actual precise theoretical settings that the camera uses, as opposed to the camera's nominal marked values. This calculator does that. To show an example of the nominal marked numbers vs the precise theoretical numbers, f/11 at 1/60 computes EV 12.826. However using the actual real values of f/11.314 at 1/64 computes exactly EV 13.00 (the correct value). Techie details maybe, but that's how it works.

The log2 is needed because the basic concept is 2EV = N2/t   (1 EV being 1 stop = 2x exposure).

(f/1 / 1 second) is 1, and any log of 1 is 0, because any number to exponent 0 is 1.
So, f/1 at 1 second is EV 0.
To compute log2, then log2(X) is log10(X) / log10(2), or which is log10(X) / 0.3.

We should have seen logarithms in high school math. We all know that addition/subtraction and multiply/divide are opposite, or inverse, or reverse operations, one undos the other, so to speak. Exponents and logarithms are the same reverse relationship. Log2 of X just gives the exponent of 2 which will give X. EV is important because a one stop change (which is 2x) is called 1 EV. EV is the powers of 2 relationship of a light intensity ratio X.

The EV formula simplistically appears not to involve ISO. But clearly the inputs of camera f/stop and shutter speed settings that it computes obviously are chosen to reflect whatever the current ISO is (to match the scene). If we imply the settings are a correct exposure for a scene, then ISO is already factored into those settings. Other ISO choices would certainly require different settings and different EV. So in that sense, EV already includes effect of ISO. You might hear opposing notions, but see the pictures of the light meter above. ISO obviously affects EV, big time. But with no risk of controversy, we are certain that EV converted to ISO 100 equivalent EV (called Light Value, next below) is absolutely dependent on ISO. We arbitrarily compare it to the exposure at ISO 100.

But we don't need EV chart versions for each ISO. You only need to know what your EV and ISO are. Then there is only one standard EV chart. It does work for any ISO, for whatever ISO is, and ISO certainly does change the settings selected. We will see a different EV number for other ISO (EV is other rows of equivalent settings in chart), but there is just the one standard EV chart.

The EV chart (below) is just the collection of EV values for all values of f/stop and shutter speed. Any possible combination of f/stop and shutter speed appears on only one row in the EV chart. The EV number is that one row in EV chart where our f/stop and shutter speed appear. The row is the set of Equivalent Exposure settings, and the camera settings on this EV row apply to the one specific ISO appropriate for a proper exposure. Or, if we meter EV xx at some ISO, then EV xx is the one EV chart row which contains the correct exposure settings, for that ISO. When using EV, ISO seems pretty much the entire point of different EV numbers. But there is only the one standard EV chart.

Light Value = EV100 + log2 (ISO / 100)   When we add ISO, we have exposure representing a light intensity. Comparing to ISO 100 allows a standard comparison. This conversion from ISO 100 is called Light Value (LV), using this additional added factor to change to EV for ISO. ISO 100 is arbitrary, 100 is Not special to the physics, we are simply just familiar with ISO 100 results. The log of a fraction is negative, so the general EV effect of changing ISO1 to ISO2 is EV + log2(ISO2/ISO1) with ± sign determined by the log of the fraction. This LV formula simply matches ISO being X stops different from ISO 100 with an EV that is X stops different too. To be equivalent exposure, settings for this new EV require using its specific row in the EV chart.

Note the subscript EV100. This formula is for conversion **FROM** 100 to some other value, adding some higher value. So any conversion **TO** 100 has to be use Minus, subtracting some higher value. Both uses cannot go the same way. The calculator above, and on the previous Exposure Comparison page convert **TO** 100, and use minus.

So Light Value as commonly seen just means equivalent "EV at ISO 100" (in ExifTool for example). ISO 100 is not a magic number, and is not necessarily the ISO or settings that the camera actually used. The 100 is only special here because the formula arbitrarily chose to use 100. It is just an arbitrary ISO reference for comparison, and is not trying to imply the scene light level by imagining settings at ISO 100 are somehow more meaningful than the ISO the camera actually used to get the picture. We can only directly compare overall exposure settings if at the same ISO. That might as well be ISO 100 because we use it a lot, but it does not make the chart be only about ISO 100. In that way, Light Value does makes it seem like the EV chart must represent ISO 100, but only because we arbitrarily chose ISO 100 as a reference. But to make meaning of Light Value, you better know the convention is that it does represent ISO 100. The exposure calculator at this site uses EV at ISO 100 only to compare two exposures at the same ISO. Any ISO would do that, ISO 100 is not a magic number, only a common number. ISO 100 is technically not even a full stop, we just make it seem so.

The term Light Value arbitrarily uses EV at ISO 100 to specify the scene light level, but ISO 100 might not always allow usable (selectable) camera settings for that exposure.

Is the EV chart for ISO 100? We might be more familiar with ISO 100, but ISO 100 is just a number, not special. The EV chart has infinitely wider use, for any ISO. However, it is common practice for camera manufacturers to specify a certain luminance as an EV at ISO 100, as when specifying metering range or auto focus sensitivity. It is a way for them to specify luminance that we would understand. When they say "EV at ISO 100", then what they mean is these camera settings if at this ISO. For example, the Nikon DSLR cameras specify their metering exposure range as 0-20 EV, qualifying that these numbers apply to a f/1.4 lens at ISO 100. If it is said that some EV statement applies to ISO 100, then the statement is about ISO 100. Light Value is computed to be EV at ISO 100. EV should not be confused with Light Value, but the combination of EV and any ISO becomes a light value.

So Wow, the EV chart must be for ISO 100, right? So sorry grasshopper, no, that's not the correct interpretation. That's all an arbitrary choice. If we use any other ISO value, like 800, the bright sun meters about EV 18 at ISO 800, and then the chart also provides the correct camera settings for ISO 800 and EV 18 (if assuming bright sun again). The formal LV itself simply arbitrarily chooses to compare at ISO 100 (it being a common value).

Yes, the chart does give correct EV values for ISO 100 settings. However, that's not special, it also gives correct EV values for any ISO we are using. ISO 100 is just another number, and the only importance of ISO 100 is that we may commonly use it. ISO 100 may be a common standard for "us", but the EV meter and EV chart use any ISO value, specifically the one we are using.

For example, we learn that Sunny 16 in bright direct sun is near EV 15, but that is only true if we are also referring to ISO 100. Technically, EV 15 is 1/125 second at f/16 at ISO 100. Sunny 16 will call it 1/100 second at ISO 100 (within 1/3 stop), but Texas bright sun near midday does meter near EV 15 at ISO 100. However, the same bright sun will meter EV 18 if we choose ISO 800. The proper exposure at ISO 800 will require different camera settings, and those different settings are the different EV value. So any exposure will have other EV values at other ISO. And the same EV chart shows that just as well too, same thing for any ISO.

An interesting point is that Light Value (LV) is the same number as EV only if at ISO 100, which can make the EV chart seem to be for ISO 100 (because the EV chart agrees with LV at ISO 100). But of course we are fooling ourself, this is Only because we arbitrarily specifically referenced LV to ISO 100. LV formula could have used any number (but 100 does seem convenient). The EV chart is in fact instead about whatever ISO we may be using at the time. EV is computed from the camera settings, which are chosen for the ISO we actually are using.

The EV Chart

The EV chart shows camera shutter speeds, in seconds. It "shows" nominal stops, but it computes precise stops. The combination of a f/stop with a shutter speed is the camera settings which comprise the EV value. Any such combination can appear on only one row of the chart (row is called EV). The EV chart is about the numerical combinations of the shutter speed and f/stop values, and the resulting exposure at some ISO. Specifically, an EV row is the list of Equivalent Exposures for that EV. ISO is also an exposure factor, it matches the settings to the light. Instead of computing the math, the chart could be drawn by just starting at f/1 at 1 second is EV 0, and then adjacent values differ by one stop.

Again, the formula and the chart are NOT about any specific ISO value, until we insist our use certainly is about the specific ISO we are using. Yes, the EV number is affected by the ISO we choose. In that the chart settings that we select are about whatever ISO we are currently using. Higher ISO increases the EV number for the same scene light value (needing different camera settings).

In normal usage, if your light meter meters bright sun to be EV 18 at ISO 800, then you look up EV 18 in the chart, which row gives the Equivalent Exposure settings for use to give a correct exposure at ISO 800. f/16 at 1/1000 second for example. The scene light is NOT EV 18. The camera settings are EV 18 to match the scene at ISO 800.

If using ISO 100 and the light meters as EV 15, the correct camera settings are on the EV 15 row.

If using ISO 800 and the light meters as EV 18, the correct camera settings are on the EV 18 row.

If using ISO 800 and then converting to ISO 100, that's the same -3 EV that we would always expect.

The camera's nominal shutter speeds are shown (seconds), except there are no nominals longer than 30 seconds, so then the precise actual values in seconds are shown instead (2048 seconds is 34 minutes and 8 seconds).

Three EV charts are provided, the standard one for full stops, and for completeness, also charts of third, or half stops. Those two are optional to view. You can make them a little smaller, but they can be pretty large, fast, and unsuitable size for a small viewing screen. The "Show" checkbox toggles them on or off.

Show EV charts from EV to EV
and from f/stop to

EV chart for nominal Third stops   Click to Show

EV chart for nominal Half stops     Click to Show

Standard EV chart of nominal Full stops


FWIW, if curious about the nominal full 2x stops being uneven shutter speed progressions of 1/8, 1/15, 1/30, 1/60, 1/125 seconds, then see the explanation.


Menu of the other Photo and Flash pages here.   Sunny 16 is on next page.


Copyright © 2011-2017 by Wayne Fulton - All rights are reserved.

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