Sunny 16 rule

File:A. W. Jones Heritage Center, St, Simons, GA, US.jpg

Sunlit subject shot on a digital camera set to ISO 100, exposed at f/8 at 1/400 second which is the same exposure value as f/16 for 1/100 second, the recommended "sunny 16" exposure

In photography, the sunny 16 rule (also known as the sunny Template:F/ rule) is a method of estimating correct daylight exposures without a light meter. Apart from the advantage of independence from a light meter, the sunny 16 rule can also aid in achieving correct exposure of difficult subjects. As the rule is based on incident light, rather than reflected light as with most camera light meters, very bright or very dark subjects are compensated for. The rule serves as a mnemonic for the camera settings obtained on a sunny day using the exposure value (EV) system.

Using the rule

The basic rule is, "On a sunny day set aperture to Template:F/ and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting] for a subject in direct sunlight."<ref name="suess">Template:Cite book</ref> In simplest terms, bright sun = f:16 @ 1/film-speed-number (aperture and shutter speed, respectively).

For example:

• On a sunny day at ISO 100 ("100 speed film"), the aperture is set to Template:F/ and the shutter speed (i.e. exposure time) to Template:Sfrac or Template:Sfrac<ref>Template:Cite book</ref> seconds (on some cameras Template:Sfrac second is the closest available setting to Template:Sfrac second).
• On a sunny day at ISO 200 and aperture at Template:F/, set shutter speed to Template:Sfrac or Template:Sfrac.
• On a sunny day at ISO 400 and aperture at Template:F/, set shutter speed to Template:Sfrac or Template:Sfrac.

Shutter speeds can be changed as long as the f-number is adjusted accordingly, e.g. Template:Sfrac second at Template:F/ gives equivalent exposure to Template:Sfrac second at Template:F/. Exposure adjustments are done in a manner that retains the EV. As the aperture is opened (f:11, f:5.6, f:4, etc.) the shutter-speed/exposure-time is reduced by a factor of approximately one-half (1/250, 1/500, 1/1000, etc.) This follows the mathematical relationship between aperture and shutter speed where exposure is inversely proportional to the square of the aperture ratio and proportional to exposure time; thus, to maintain a constant level of exposure, a change in aperture by a factor c requires a change in exposure time by a factor Template:Sfrac and vice versa. A change in the aperture of 1 stop always corresponds to a factor close to the square root of 2, thus the above rule.

Alternative rule

The sunny 16 rule can be used in varying light by setting the shutter speed nearest to the ISO film speed and f-number according to a generalized exposure table, as:<ref>Template:Cite book</ref><ref>Template:Cite book</ref>

File:Tessina with exposure guide plate.JPG

Tessina with exposure guide plate from the 1960s. At that time, DIN 21 was equivalent to ASA 80. After 1983, DIN 21 was ASA 100.<ref>Ilford Manual of Photography p. 415, 1981</ref> On this guide plate, DIN 21 uses f/16 and 1/125, consistent with Sunny 16.

Aperture	Lighting conditions	Shadow detail
Template:F/22	Snow/sand	Dark with sharp edges
Template:F/16	Sunny	Distinct
Template:F/11	Slight overcast	Soft around edges
Template:F/8	Overcast	Barely visible
Template:F/5.6	Heavy overcast	No shadows
Template:F/4	Open shade/sunset	No shadows
Add one stop	Backlighting	n/a

See also

• Looney 11 rule

External links

• Guide to Photography Sunny 16 and film exposure guide.