How many stops difference? What are the EV numbers? Find an Equivalent Exposure?
Want to know the value of f/6.3 + 1.67 EV of exposure?
There are three modes here:
The fields in this calculator can use third or half stops. The selectable values are marked if half stops, and you should not mix third and half values if your camera is not set to use them. If wanting to compare individual relationships (differences of two fstops, or shutter speeds, or ISO), there is another another calculator for that.
The selections above provide the possible camera settings. Half stops are marked with *½.
The calculator range of Nominals is outrageously large, but not quite infinite.
The wide range prevents some extreme computed settings from going out of range, but extremes could still make that possible.
EV may seem to read sort of backwards, in that an Absolute EV value of greater EV means more light is present, and necessarily needs less exposure to compensate it. The values in the EV Chart (next page) makes that obvious.
However, in the camera, +1 EV Relative compensation does boost our settings to 2x greater exposure. For the calculator's exposure difference, it is Relative and +EV is more exposure, and I also try to directly specify that more and less refers to Exposure in that case.
In the calculator:
Exposure Difference makes comparison of two exposures possible by first converting both EV results to ISO 100 (as if metered at the same ISO value). This arbitrary conversion to ISO 100 is called Light Value (more on next page). ISO 100 is just a number, NOT magic nor unique nor special in any way in the EV system. We could have used any number, but ISO 100 is simply familiar and comfortable for us. ISO 100 is convenient, but ISO 100 is absolutely NOT SPECIAL in any way, it's just a number, one among many, and only its popularity might make it seem special. That is true in the EV Chart too. The EV Chart is for any and every ISO value, specifically whatever one you are currently using. ISO 100 is NOT special in any way relating to EV.
Logarithm and exponent are inverse operations, like are multiply and divide or add and subtract (one undoes the other, so to speak), so ...
EV is just powers of 2 (so that 1 EV = 2x value). There is another math page if interested, but here the only point is, the Settings EV shown is computed from the two settings (fstop and shutter speed duration). ISO may not be directly in that EV formula, but make no mistake, ISO is certainly a major factor of exposure, because ISO is what determined the exposure choice of those two other settings. The Absolute EV number alone is simply not meaningful as an exposure without specifying the corresponding ISO number. That EV is the exposure that a light meter would read if set for that ISO. So ISO is absolutely an EV factor (EV is Exposure Value), and if in a film camera, settings EV of f/stop and shutter speed applies to whatever film speed is in the camera that caused selection of these settings. The exposure EV uses those settings AT THAT ISO. The set of the corresponding Equivalent Exposures are those on the EV row in the EV chart. The same EV Chart is applicable for any and every ISO value, i.e., specifically whatever ISO you are currently using.
The camera settings EV term might be misunderstood, because it is computed from only the shutter speed and f/stop values (a calculator is on next page). This Settings EV is seemingly independent of ISO, except the EV number is computed from the camera settings already chosen for whatever appropriate ISO is in use, which makes ISO in fact be all important. Numerical EV was developed when light meters were to be added into film cameras (late 1950s, implemented early 1960's) to aid computing exposure. Then film speed (called ASA then, ISO today, same numbers) was a temporary constant determined by the choice of the roll of film in the camera. This ISO number was identified to the camera, so the metering knew it and could compute how much the camera settings needed to change to match exposure to this film speed. The settings combination of f/16 at 1/125 second is numerically EV 15 for any ISO, but those settings are chosen specifically for and only applicable for the one specific ISO currently being used. So maybe the formula to calculate EV does not include the ISO number, but the choice of the proper camera settings used certainly depends on ISO. The camera settings are not necessarily a correct exposure unless ISO does match them to the scene. More on next page (EV Chart).
The calculator default numbers represent full bright direct sunlight. The way the exposure is said is 1/2000 second at f/11 (EV 18) at ISO 800. An equivalent is also 1/125 second at f/16 (EV 15) at ISO 100 (is EV 15100, and is initial default of calculator, or other Equivalents, like 1/250 at f/11 at ISO 100 (also is EV 15100). All of these are the same exposure. However the Absolute EV number alone is not meaningful without specifying the corresponding ISO number.
That settings EV is that Exposure Value that a light meter would read when set to that ISO. It is how the EV Chart would be used, we would use the settings on that indicated EV chart row, for the proper metered exposure at that ISO (example next page). EV is technically computed from only the camera settings (only shutter speed and f/stop are computed), but those choices course depend on the ISO value. The one EV chart is for ANY AND EVERY ISO value, meaning specifically whichever chosen one is in use. If we change ISO, it changes the metered EV and the settings we would select.
ISO: That settings EV is the row in the EV chart where that combination of equivalent settings is found, and might appear to be independent of ISO in that way. However, when the light meter is set to an ISO and then it meters EV X, then the EV chart row X is the right settings for a correct exposure at that same ISO. ISO is very important. A different ISO would meter different settings on a different EV row. So the settings (shutter speed and f/stop) are selected with attention to the ISO (cause and effect), and certainly we do get a different EV with a different ISO.
Basically, the EV number is the "name" of the set of Equivalent Exposure combinations of f/stop and shutter speed found on that one row of the EV chart.
Light Value converts the ISO to an arbitrary but standard ISO 100 value for the purpose to compare two actual exposures at the same ISO 100 values. The number 100 is NOT a special ISO number at all, Light Value could compare by converting both readings to any same ISO number, but 100 is merely a popular convenient number. Light Value represents the corresponding relative "brightness level", so to speak, which then would require the appropriate proper corresponding exposure. More about Light Value on next page, and the formulas are on a math page. These are still the same two exposure levels (EV 18 at ISO 800 and EV 15 at ISO 100), but when both EV are converted to same ISO 100 for easy comparison, then here, both Light Values are EV 15100, or again, same light levels require Equivalent Exposures (at the same ISO 100). The Settings numbers may not have been Equivalent, but the resulting brightness level (adjusted for ISO) of the two Light Values of the exposures are the same, and Equivalent.
Exposure Value and the EV Chart is covered on the next page. But either of the initial default settings above give the same equivalent metered exposure in typical bright sunlight. Both A and B are also the Sunny 16 Rule (except Sunny16 is often 1/3 stop more exposure than the EV system meters). The actual meter doing this is shown on next page. This is two actual real world meterings of two equivalent exposures.
That concept is, for the two ISO values, the light meter reads EV 15 or 18. Look up either EV 15 or EV 18 in the EV chart, and it will show these settings appropriate for that ISO. That's what the chart's about. Since ISO 800 exposes 3 EV brighter, it offsets the faster shutter speed, so these two are Equivalent Exposures. The purpose of this calculator is to similarly compare any two exposures.
The calculators top "EV (settings)" value is computed from the settings entered, and (assuming a correct exposure) is what a light meter will read at the working ISO, and this is the EV to look up in a EV chart for use at that ISO value. The actual camera setting choices will have already been affected by that ISO, so this EV is not further affected by the ISO that we enter now.