Copyright © 2014-2024 by Wayne Fulton - All rights are reserved.
How many stops difference? What are the EV numbers? Find an Equivalent Exposure?
Want to know the settings 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 half stop values are marked, and you should select whichever your camera is using, and Not mix third and half values. Full stops are marked in Yellow. If wanting to compare individual relationships (differences of two fstops, or shutter speeds, or ISO), there is another another calculator for that.
The calculator's initial default is that a change in any field will recompute results, which seems nice much of the time. But since there are multiple settings, then if you dislike seeing each unwanted setting change before you're ready, the top checkbox can choose to recompute ONLY when the Compute button is clicked (when you are ready to see it). But then the previous result becomes not necessarily correct, so will Not show until the Compute button is clicked (or the top checkbox is turned off). So you must remember to click Compute, but if that is confusing, don't choose that option. If you turn "any change" back on, it will immediately recompute.
The selections above provide the possible camera settings. Half stops are marked with *½.
EV may seem to read backwards, in that an Absolute EV value of greater EV means more light is present, and necessarily needs less exposure. The values in the EV Chart (next page) makes that obvious.
In the camera, +1 EV Relative compensation does boost our settings to 2x greater exposure when there is less light. The calculator's exposure difference is Relative and +EV is more exposure, and it tries to directly specify that more and less refers to Exposure.
Just for a reference, the brightest sun in the clearest sky will be right at EV 15 at ISO 100. Normal bright conditions might often be 1/3 EV less (humidity, haze, etc).
The calculator range of Nominals is ostentatiously large, but not quite infinite.
The wide range prevents most extreme computed settings from going out of range, but extremes could still make that possible, which might take a couple of tries.
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 an arbitrarily chosen number, NOT magic nor unique nor special in any way in the EV system. We could have used any number, but ISO 100 is used for Light Value because it 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. My song and dance is that is that ISO 100 is Not Special in the EV Chart either. The one EV Chart is for any and every ISO value, specifically whichever one you are currently using. ISO 100 is NOT special in any way relating to EV. When you change ISO, the appropriate settings simply move to another row in the EV chart.
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, as used in photography). There is another photo 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). The EV system was developed about 1960 as light meters were being added into cameras (EV differences were just called "stops" before), but in 1960, the ISO was in fact a constant until the film roll was changed. EV is used two ways, as the Absolute EV for the current exposure, or as the Relative EV difference between two settings.
So ISO may not directly be in that one EV formula (Relative), but there is another Absolute exposure formula where it is used (the "two way" link in sentence immediately above), so make no mistake, ISO is certainly a major factor of exposure, because ISO is what determined the exposure choice of those other two settings. The Absolute EV number alone is simply not meaningful as an exposure without specifying the corresponding ISO number used. That Absolute 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 one EV Chart is applicable for any and every ISO value, i.e., specifically whichever ISO you are currently using.
So NOTE: The EV Number depends ONLY on f/stop and shutter speed, but which settings were undoubtedly chosen to work with the ISO being used.
So when we hear clearest sunlight is about EV 15, that conventionally means at ISO 100. The same exposure is EV 18 if ISO 800 (3 EV difference). When you might say some exposure is f/8 at 1/1000 second, that is meaningless (for exposure purposes) unless you also specify at which ISO.
SO UNTIL the settings are changed for the new ISO, this specifically means the settings EV Number for any ISO is the same EV Number for any other ISO. However, that Exposure would of course vary with ISO too. But then resetting Equivalent Exposures will change f/stop or shutter speed for a different ISO to become Equivalent exposure.
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. ISO is definitely all important to exposure. 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 the ISO we are using (example next page). The EV number is computed from only the camera settings (only shutter speed and f/stop are computed), but those setting choices of 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 conventional ISO 100 value for the purpose to compare two actual exposures at the same ISO 100 values. The number 100 is just another number, 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. If you're not using ISO 100, then you would have to convert that 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 math formulas are on a math page.
We say bright sunlight meters EV 15, but that means if at ISO 100. ISO 800 would read EV 18. EV 15 at ISO 100 and EV 18 at ISO 800 are the same two exposure levels, but as comparable Light Values, both EV are converted to same ISO 100 for easy comparison. 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.
Copyright © 2014-2024 by Wayne Fulton - All rights are reserved.