Camera exposure in bright direct sun is often seen to meter near EV 15 at ISO 100 (one of those EV 15 equivalent exposure choices is 1/125 second at f/16. Sunny 16 uses 1/100 second at f/16.)
Sunny 16 is another general rule of thumb we should all know, a very old guideline for determining outdoor daytime camera exposure without a light meter. I've mentioned it a few times, used as an automatically assumed notion of proper exposure under bright sun. The idea is that since the bright sun is a constant, it always provides the same exposure. The Sunny 16 rule says that the exposure for frontal lighting in bright sun is f/16 at 1/ISO seconds (all Equivalent Exposures work too). So, Sunny 16 in bright direct sun with ISO 100 is 1/100 second at f/16, or 1/200 second at f/11, or 1/400 second at f/8, etc. EV 15 in bright sun is ISO 100, 1/125 at f/16, or 1/3 stop different than Sunny 16. But it’s close. The Sunny 16 Rule dates from the days when we used B&W film, and 1/3 stop was easy correctable for negative film, which is always simply adjusted when printing in the dark room. But exposure is more critical for digital (or for positive film slides). However, for any case dimmer than brightest sun, Sunny 16 involves human guesses about shadow intensity, which can be surprisingly close, but it is not as accurate as actually metering the light.
The f/16 in the rule is only important because it matches the 1/ISO shutter speed at ISO 100 in bright sun. But f/16 ISO 100 is also equivalent to f/22 ISO 50, or f/11 ISO 200, etc. Use the equivalent combination of best use for you. One of the oldest rules used by news photographers was "f/8 and be there" (depth of field also depends on their view camera's focal length). Landscape and macro photographers may tend towards equivalent exposures with f/22, and there are times for f/2.8 or f/4, but if the light is adequate, f/8 is really hard to fault.
Sunny 16 exposure charts also include approximations of lighting conditions which cause steps of one stop changes of exposure. You would open additional stops for degrees of cloudy, overcast or shade, which are judged by noticing the shadows. This will vary, because our eye cannot judge exactly, so we should learn to use our light meter, it is normally better, and that's what it's for. But we should also always notice the shadows, they give good information. The direct sun casts sharp shadows under people or things. We can notice those shadows. Sunny16 can help if we don't have the light meter.
Shadows in Sunny 16 are technically not precise, and which did work better for negative film (negative film had more latitude than digital, and saw advantage in overexposure of shadows, plus the film processing guy corrected the prints too). Light meters do have an advantage, important for slides and digital today. But if no light meter, Sunny 16 and the shadows can be a big help for estimating exposures in outdoor daylight.
Back in the day, every roll of film came with a data sheet that included a similar exposure chart, used before cameras had built-in light meters. This seemed normal, but photography was harder work than today, with no light meter, and no automation, and we couldn't see the result until later (when no longer at the scene). Bracketing helped difficult cases, but we also learned to think about what we were doing. And the B&W negative film had greater latitude which allowed more leeway. Dark room work could fix it (as can shooting raw today). But my notion of the significance of Sunny 16 for digital today is this: If you have access to a light meter, go with it, learn to use it, that's what it's for. If no metering capability is available, Sunny 16 may not be precise, but it can get close to the ballpark for many outdoor scenes. And when there is doubt about your metered value, knowing Sunny 16 can be a confirmation of reasonableness.
In bright sun, Sunny 16 implies any Equivalent Exposure of f/16 at shutter speed at 1/ISO seconds (i.e., ISO 100 uses f/16 at 1/100 second, or equivalents, like f/8 at 1/400 second). This assumes frontal lighting, from two hours after sunrise to two hours before sunset. Side or back lighting will need another stop or two of more exposure.
|Sunny 16 Rule||Shutter speed 1/ISO seconds, or Equivalent Exposures|
|F/stop||Lighting conditions||Detail of Shadows|
|f/22||Water/sand/snow||Added Reflections||Much bright reflection adding to the direct light|
|f/16||Sunny||Distinct dark shadows||Normal bright sun|
|f/11||Slight overcast||Soft around edges||Softer shadows - Or maybe only 1/2 stop if just Hazy|
|f/8||Overcast||Barely visible||Vague trace of shadows|
|f/5.6||Heavy overcast||No visible shadows|
|f/4||Open shade/sunset||No shadows||Open shade is illuminated by clear sky overhead|
Sunny 16 is an incident method, and is not affected by the subjects reflected colors. The method was a big deal in the days before light meters were common. It is not metered, and instead approximates the daylight light intensity by judging the shadows. It’s not precise like an incident light meter, but is the same concept of trying to judge the actual light level. Whereas a reflected meter only sees reflected light affected by subject colors, and makes exposure of all scenes average out to be middle gray (see metering), so white scenes will be gray (underexposure), and black scenes will be gray (overexposure). If using the reflected camera meter, white snow needs additional compensation to be white instead of gray (probably +1 or +2 EV compensation, perhaps more). An incident meter will get it right (it is aimed at the camera, away from subject, metering the actual light).
Note the f/22 Sand, Snow, Water is a different concept here. The Sun is no brighter, but these are highly reflective beach scenes, or snow fields. The f/22 idea is more about the sum of added reflections from water, sand or snow, brighter and increasing exposure, but it may make the shadows on the face be actually somewhat diffused, as you'd expect. Some sources may describe it's shadows as "Dark with sharp edges", but I'm not sure they get it. It is the same sun, but with added accumulated intensity from reflections.
Sunny 16 is Not point & shoot. Instead, we need to actually think a second about what we see first. Great for brighter levels, however lower light levels in shade can get quite vague, and it's of no use indoors.
In general, Sunny 16 is a good safety check to consider if your metered exposure is plausibly reasonable. Remembering that can help us to rethink abnormal metering results.
Back in the negative film days, the standard saying then was "Expose for the Shadows", suggesting intentional ample exposure of shadows, and allowing overexposure of highlights (which did not hurt negatives much, they had wide latitude in the dark room). However, that applied only to negative film (which will be inverted). "Expose for the shadows" was NOT a good plan for positive slide film, and is also especially bad for digital, because of the overexposed highlights, and digital clipping. So the opposite rule for positives was "Expose for the Highlights" (meaning "don't burn out the highlights, and don't clip anything in digital"), which is still very applicable to our digital cameras. Today, positive digital images are more demanding than negative film, due to less latitude, and digital clipping, etc, so clipping due to overexposure becomes a Real Bad Thing now. However, film negatives actually enjoyed a modest amount of it.
For bright sun and ISO 100, Sunny 16 is 1/100 second at f/16 and EV 15 is 1/125 second at f/16. That's close, within 1/3 stop, but which is it? But in fact, it might meter either way.
Sunny 16 was all that we had at first, originating before light meters were common, and also before camera settings even offered third or half stops. Technically, 1/128 second was a full stop then (the actual even power of 2), and 1/100 second (called ASA 100 in those days) was a third stop. But the older cameras did not do third stops, so we had Sunny 16 calling it 1/100 second, and print processing could easily tweak exposure of negatives. Later when cameras began building automatic light meters into cameras in the 1960s, EV nomenclature was invented, and ISO film speeds were recomputed so that ISO 100 will in fact be a full stop (instead of ISO 128). So now EV 14.67 is 1/100 f/16 ISO 100 and EV 15 is 1/125 second f/16 ISO 100 (the math of this, near page bottom). Either one might be encountered in apparent bright sunlight. I loved Sunny 16 back in the day of negative film, and exposure was generally easily correctable during darkroom printing, but today my bet is on the metered EV. Both will vary a bit.
The concept is that the Sun gives a constant exposure, however the sky clarity does vary. Weather, haze, humidity, pollution, hour of day, season of year, elevation, latitude, old uncoated lenses, side or rear lighting, and clouds, all can affect it somewhat. Depending on haze and humidity, bright sun at ISO 100 does not always meter as much as EV 15, nor does Sunny 16 always reach its peak. Due to the angle though the atmosphere, the sun's light does vary slightly with latitude on the earth, and with the seasons, brighter at equator or in summer. Just slightly, but Kodak in Rochester NY was near 45 degrees. And sunlight varies at early and late time of daylight, and at altitude (mountains). An even larger factor is that side and rear lighting needs increased exposure. Sunny 16 applies to frontal lighting, from mid morning to mid afternoon (at least two hours from sunrise or sunset).
A third of a stop should not be a surprise when guessing, which was a very minor problem in negative film days, which had considerable latitude, and the print exposure required adjustment in the darkroom anyway (when printing). If shooting B&W negative film, substantially more exposure may be desirable anyway to enhance shadow detail. The old rule of "Expose for the Shadows" was advice for negative film, but that DOES NOT apply to color slides or digital, when preventing overexposure of highlights becomes more important.
Here is some background:
EV 15 is speaking of an incident meter reading, directly metering the actual light incident on the subject. Whereas a reflected meter (camera meter) reading varies with the reflectivity of the subject colors, when observing the subject is another skill we do need to master.
Sunny 16 is just ballpark. We cannot judge the shadows precisely, not to within 1/3 stop, but with practice, we can get better at it. And we ought to always notice the shadows, they are a strong clue of the lighting.
Sunny 16 is just a general rule of thumb, applicable to a few standard situations outdoors, an approximation used in the early days of negative film. Sunny 16 was the only guide we had before light meters were common, and it worked pretty well for negative film. Because negative film had wide latitude, was easily corrected in the dark room, and the photo finishers in fact helped us a lot, correcting exposure, and later correcting white balance and color too. We could use either the clear or the blue flash bulbs indoors, and then they fixed it for us, and we might never realize there was any issue. Sunny 16 is harder for digital cameras now (no dark room), so we also have to do our own digital corrections now too (no one else is going to fix it now).
But a little overexposure was a plus for negative film, it added detail in shadow areas. Until 1960, Kodak B&W film speed (which used ASA since 1946, American Standards Association, before ISO) was intentionally specified as half of what the speed actually was (an intentional safety factor against underexposure). The first selenium cell light meters were in the 1930s (not very sensitive to low light), but light meters in cameras did not happen until the transistor era, about 1960. Light meters in cameras were becoming popular about then, and in 1960, Kodak doubled the ASA speed number for their negative films. This was Not a change, the film did not change. Kodak simply doubled the printed number, eliminating the previous speed safety factor. Again, film negatives enjoyed a little overexposure, but when cameras started actually metering, this became noticeable. This was a Big Event, but everyone already knew to double the boxes film speed. This double rating in 1960 affected B&W European DIN film speed ratings too, which is a logarithmic scale, adding 3 doubles the speed, starting at ASA 1 = DIN 1. 10 × log10(2) = approx 3, so ASA 100 is DIN 21, and ASA 200 is DIN 24.
ISO (International Organization for Standards) adopted the same ASA numbers in 1974, no difference in the numbering (format often written as ISO 100/21).
Bright sun usually meters (up to) EV 15 (at ISO 100). Specifically, EV 15 is 1/125 second f/16, 1/3 stop faster exposure (less exposure) than Sunny 16 for ISO 100. Some instructions said to always increase Sunny 16 shutter speed to the next Full stop (because cameras only had full stops back then), which is 1/125 second (Both 1/125 second and EV 15 are full stops). Film charts often said 1/125 second at f/16 (or equivalent 1/250 at f/11). Because again, full stops were normally the only choice on older cameras. More precision was mechanically difficult, and precision really wasn't critical for B&W negative film (the result was handled in the darkroom).
I doubt we know the first use of the term Sunny 16, but from the beginning, there were always similar daylight exposure charts (values for bright, cloudy, overcast) since Daguerreotype days in 1840 (which was about six minutes in bright sun initially, but later was less than one minute). Emulsion speed improved fairly rapidly, but a very special case was that Muybridge developed high speed emulsions and shutters for his 1872 galloping horse (I've heard it was a 1/2000 second shutter, with flashes along the background so the horse was in silhouette, and it had never been done.) Kodak's first 1888 box camera was 1/25 second f/9, which for bright sunshine might be ISO 6.
Actual literal Sunny 16 could come only after we had film speed ratings. However, there were several different early film speed rating systems, and therefore, early light meters in the 1930s specified their own film speeds for various films (before standards). The first Weston light meter was in 1932. Hollywood and Ansel Adams had them, but it was the Depression, and not so many others had one yet. General Electric also made light meters starting 1935. Both meter brands independently created empirical film speed ratings for use with their meters. Here's a 1942 Kodak data sheet that gives Kodak, Weston, and GE film speeds (before ASA), and the ever-present exposure chart. The GE rating approximates the later ASA rating (before ASA speeds were doubled in 1960). General Electric meters switched to use ASA when the standard was defined in 1946. Weston meters did not switch to ASA until the mid-1950s, after which ASA 125 corresponded to older Weston 100. This difference is 1/3 stop. The EV system did not appear until the late 1950s. ISO film speed specification adopted the ASA numbers in 1974 (called ISO since then).
But no one changed the Sunny 16 charts then, or the 1/film speed concept when we modified the film speed. But that popular Weston meter system shift might explain the slight 1/3 stop discrepancy between EV 15 and Sunny 16. There is also the fact that 1/100 second is a third stop, and camera shutters back then only had full stops, so we had to round 1/100 to be 1/125 second (which then matched EV 15 anyway). And the direct bright sun is often seen as a bit less than EV 15 at ISO 100 (due to moisture and air and altitude and angle, etc).
Every box of consumer film included a data sheet with a similar exposure chart, which was used outdoors without a light meter. The charts were not named Sunny 16, but it was the about same thing, at least the same concept, including watch the shadows, and open a stop or two for cloud cover. However even after ASA ratings, they were not all exactly 1/ASA seconds at f/16. Back in the day (through the 1960s), our cameras only had full stops. Mostly these charts were close to Sunny 16. Kodak data sheets always specified only full stops. Kodak ASA 64 sheets said bright sun was 1/125 at f/11. ASA 125 and ASA 160 mostly said 1/250 at f/11. ASA 400 said 1/500 at f/16. These were all full stop shutter speeds, and back then, full stops was all our cameras could do.
Times were different back then, and here are sample modern data sheets for those who have never used film, at least not without todays automation. Kodak Plus-X Pan speed was ISO 125, which matched a full stop shutter speed, so recommendations were Sunny 16. But Kodak Tri-X Pan ISO 400 speed was not a full stop, and it specified 1/3 stop faster shutter speed than Sunny 16 (1/3 stop less exposure, like metered EV). That seems no doubt because cameras only had full stop settings then. But film speed was not especially critical for the wide latitude of negative film. In fact, a little intentional overexposure was considered a plus for B&W negative film shadows. But digital needs to be closer today.
So Sunny 16 (and judging the shadows) is a little vague, just a ballpark rule of thumb, requiring a bit of thinking about the light. Lighting conditions are always vague unless we meter it. I was a big fan of Sunny 16, but times change, and I use light meters today. Sunny 16 indeed was a good general rule for a simpler day (before light meters, no alternatives then). We used B&W negative film back then, which had much more exposure latitude, which made a big difference. And for exposure, the darkroom work offered the same attention and benefit as the tweaking of Raw images today. Sunny 16 is still the same that it always was, but for digital work today, it is less precise than actually metering the light.
Still, Sunny 16 definitely is an important and honored fundamental to know. The Sun is a constant (but weather is not). Actually seeing and recognizing the shadows is quite important to photography. When taking a picture of someone outdoors, do you notice what kind of shadow they are making on the ground? That shadow might advise you about moving into shade first. And Sunny 16 ought to be the first thought remembered when wondering if a metered exposure is reasonable or plausible.
Reflective meters certainly do have their own problems, see how light meters work. Sunny 16 does not meter anything but the constant Sun idea is more like incident meters, or like reflective metering on a gray card, which are attempting to judge the light directly, instead of the variable reflection from the subjects colors.