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 is another general rule of thumb we should all know, an old guideline for determining outdoor daytime camera exposure without a light meter. I've mentioned it a few times, 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 of course). 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 close. 1/3 stop was nothing for negative film, but is more significant for digital.
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" (of course, 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 of course 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 of course 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. 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 Exposure|
|F/stop||Lighting conditions||Shadow detail|
|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 for Hazy|
|f/5.6||Heavy overcast||No shadows|
|f/4||Open shade/sunset||No shadows||Open shade is illuminated by clear sky overhead|
Sunny 16 is not affected by the subjects reflected colors. It is not metered, and instead approximates the daylight light intensity by judging the shadows. Of course not precise like an incident light meter, but 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, for maybe highly reflective beach scenes, or snow fields. Many sources may describe it's shadows as "Dark with sharp edges", but I'm not sure they get it. The f/22 idea is more about additional reflections from water, sand or snow, brighter (and coming back upwards too), but it may make the shadows on the face be actually somewhat diffused, as you'd expect. It is of course the same sun, but with added accumulated intensity reflections. About sand/snow/water:
Sunny 16 is Not point & shoot. Instead, we need to actually think a second about what we see first. However, lower light levels in shade can get quite vague.
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.
For bright sun and ISO 100, EV 15 is 1/125 second at f/16, and Sunny 16 is 1/100 second at f/16... then, that's close, within 1/3 stop, but which is it? When it was all we had before meters, I loved Sunny 16 back in the day of negative film, but now my bet is on the metered EV. Of course, we do encounter situations agreeing either way. And both will vary a bit.
The concept is that the Sun is of course a constant, but 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 of course 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 was adjusted in the darkroom when printing. If shooting B&W negative film, substantially more exposure may be desirable to enhance shadow detail. The old rule of "Expose for the Shadows" was advice for negative film, but did NOT apply to color slides or digital.
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, and observing the subject is another skill we need to master.
Sunny 16 is just ballpark, but with practice, we can get better at it. We cannot judge the shadows precisely, not to within 1/3 stop. But 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 white balance and color too. We could use either the clear or the blue flash bulbs indoors, and they fixed it for us, and we might never realize there was any issue. Sunny 16 is harder for digital cameras now, and we also have to do our own 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. Kodak simply doubled the printed number, reducing the speed safety factor, the film did not change. This was a Big Event, but everyone already knew to double it. 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 ASA 1 = DIN 1°, and log10(2) = 3 approx, 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 ASA/DIN, or ISO 100/21°).
But today, digital images are more demanding, due to less latitude, and digital clipping, etc, so clipping due to overexposure becomes a Real Bad Thing now. 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 a very bad plan for slide film, and is also bad for digital, because of the overexposed highlights, and digital clipping. So the rule for positive film was "Expose for the Highlights" ("don't burn out the highlights, and don't clip anything"), and is still very applicable to our digital cameras.
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 of course, 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 years 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 near 1/2000 second, but I don't know aperture. Kodak's first 1888 box camera was f/9 1/25 second, which for bright sunshine might be ISO 3 to 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 1950s. ISO film speed specification adopted the ASA numbers in 1974.
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).
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 of course always vague unless we meter it. I'm a 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 of course 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 of course, 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.