The Sunny f16 rule is really useful on bright sunny days in the spring, summer, and fall, but you can’t rely on it in winter. It will often lead you astray. There are much more accurate ways to meter in the winter.
This is the ninth in an ongoing series of articles on winter photography (links below).
A Quick Sunny f16 Summary
As long as the sun is high in the sky and not obscured by clouds, haze, dust, or other particulates in the air, it is a constant light source. That is why the Sunny f16 rule usually works in spring summer and fall (with some exceptions). The Sunny f16 rule, also known as Basic Daylight Exposure (BDE), is pretty simple. For front-lit subjects set the lens aperture to f/16 and use a shutter speed equivalent to 1 over the ISO you are using (1/ISO). If the camera ISO is set to 100, the Sunny f16 exposure is f/16 at 1/100 second. If the camera ISO is set to 400, the Sunny f16 exposure is f/16 at 1/400 second. (You can also use equivalent exposures.) As long as the subject is front-lit and not really light in tone (like white sand, white animals, and snow), or really dark in tone (like a gorilla), the Sunny f16 rule works just fine. If your subject is side-lit, back-lit, really dark in tone, or really light in tone, you will need to do some exposure compensation. The Sunny f16 rule doesn’t work for closeup photography. Details on all the ins and out of the Sunny f16 rule are covered in my book Digital Photography Exposure for Dummies (linked below).
Why the Sunny f16 Rule (BDE) Isn’t Reliable in Winter
In the winter, bright sun on snow can easily exceed the exposure latitude of even the best digital cameras, making the Sunny f16 rule unusable. This photo in a local park is an example. I used the Sunny f16 rule and much of the snow is blown out. The clouds in the sky are also washed out. The sunlight on white snow and back-lighting the clouds is just too bright. The Sunny f16 rule didn’t work.
The problem is your camera can’t see the same range of light to dark tones (exposure latitude) that your eyes can see. If you have bright white tones, medium tones, and dark tones in the same scene, your camera can’t record them all in a single click of the shutter. If you meter for a medium tone (which is also what a gray card or incident light meter essentially helps you do), the medium tone will look great, a really dark tone will disappear in inky blackness, and a bright white tone will be totally washed out. And sunlight on white snow is about as bright as it gets. To complicate matters even further, every camera’s snow exposure latitude is different. All of this comes together to wreak havoc with the Sunny f16 rule. The Sunny f16 rule gives you great exposures for medium toned (middle gray) subjects, but not bright white, snow.
There isn’t a simple exposure compensation rule to adapt the Sunny f16 rule for sunlight on snow. There are just too many variables when it comes to sunlight bouncing off of snow. You can stand in the same place in the same light, take pictures in four different directions, and the intensity of the sunlight bouncing off the snow will be different in each direction. The camera angle matters. So does the angle of the snow relative to the sunlight. If the sun isn’t high in the sky, the intensity of the sunlight is reduced by the atmosphere and the Sunny f16 is no longer applicable.
The same is true for incident light meters. They will also throw you off since they will give you a great exposure setting for medium tones, but not for bright sunlight on snow. The only way around this is to alter what the incident light meter tells you with the right amount of exposure compensation, plus make additional allowances for the snow exposure latitude of your particular camera (they are all different – see the article linked below). The same is true for metering an 18% gray card. You will get a great exposure for medium tones but not bright snow. There are better ways to meter in winter.
Let’s take a closer look at the snow in the foreground of the above photo in the area of the footprints and small tree stump.
This photo of the snow in the foreground was also exposed using the Sunny f16 rule. Most of the pixels are totally blown out. It is a bad exposure. Let’s look at the LCD image and the histogram for this photo.
“The Blinkies” (flashing black and white) show all of the overexposed, blown out pixels in the photo of the snow. There are also three spikes on the far right side of the histogram indicating blown out and almost blown out pixels. The camera is giving me two big warnings that the Sunny f16 rule didn’t work.
If your camera has the blinkies feature, you should turn it on. You should also turn on the histogram and pay attention to what it tells you. They will both warn you when you have blown out pixels, no matter the season of the year or the subject. If you have a choice between an RGB histogram and a luminance histogram (which averages all three colors), use the RGB histogram. It gives you a more complete and accurate idea what is going on with your photo. One of the color channels can be blown out, which an RGB histogram will show you, while the average of all three color channels for the same photo will look ok in a luminance histogram, giving you no clue that one channel is washed out.
When you have bright sunlight on snow, the same is true for using a gray card or an incident light meter. You still have the possibility of blown out snow due to the exposure latitude of the typical digital camera.
The Best Way to Meter Winter Scenes
The most reliable approach is to use your camera to meter just the snow (or in some cases just your subject and not the snow) and use the appropriate amount of exposure compensation for each situation, subject, lighting condition, and time of day (or night). There are several variables involved. How do you know exactly what to do? That is the reason for this series of winter photography articles.
Information for the first photo: Denali (Mt. McKinley) photographed at sunrise from Reflection Pond. Denali National Park, Alaska. Canon EOS 3 film camera. Kodak E100VS professional slide film. Exposure was based on the sunlit, east facing flanks of Denali. Exact exposure data unrecorded.
Other articles in this series
Using Reflected Light Meters, Part One (with a section on exposure compensation).
Why Is Exposure So Important? The first in a series of articles covering the basics of exposure with links to the rest of the articles.
Speaking Your Camera’s Language: Aperture, Shutter Speed, and ISO (thinking in stops).
Mastering exposure is one of the first and most important steps to becoming a better photographer. One of the best ways to do this is to read Digital Photography Exposure for Dummies and do the exposure exercises in the book. This book will teach you the basics and then take you well beyond the basics. Digital Photography Exposure for Dummies is one of the highest rated photography books at Amazon.com (5 stars) and it is praised by amateurs, professional photographers, and photography magazines as one of the most helpful and comprehensive books on exposure currently available. You can learn more here and order it at Amazon.com.