Estimating Exposure Outdoors Without a Light Meter
By Jim Pickrell
Some new digital photographers seem to have difficulty believing that you can shoot a digital camera in manual mode outdoors for most of the daylight hours without using a light meter. After all, new digital cameras all have light meters and automatic exposure modes built into them.
But 70 years ago, folks were shooting Kodachrome transparency film without any light meters. Kodak's Kodachrome was very intolerant of incorrect exposure. Modern digital cameras are similar in their requirements for correct exposure, but may be more forgiving than Kodachrome.
I did a review of Bound for Glory - American Color 1939-1943
, a book full of images of Kodachrome that were probably shot without a light meter. Kodachrome is very unforgiving of improper exposure - maybe 1/2 stop of light too little or too much and the slide was ruined.
This photo was shot in 1945 without a light meter - I know, because this is shot of your author age 1 in Fort Sam Houston Texas.
The focus wasn’t too good, but the exposure wasn’t off by much. How did my father do that??
Rather than a light meter, he almost certainly used the rule known as the “Sunny 16” which lets you estimate the exposure between 10 am and 5 pm accurately, without a light meter. You might ask why this is worth wasting your time on today when you already own a excellent meter in your camera.
The answer is that, even today, meters can give the wrong exposures, and it is always good to be able to estimate the correct exposure in your head without any tools but the understanding of the Sunny 16 rule.
Light meters get fooled when asked to meter very bright objects such as a snow covered landscapes, or a shot of the moon, or a very dark object like a black Labrador retriever. The reason meters get confused is that they assume everything in the area metered is a neutral mid range tone and then read its reflectance - the so called 16% gray card, but in the real world things are not always medium tones.
The Sunny 16 rule is based on INCIDENCE lighting, and will frequently be more accurate than most reflected meter readings that depend on the reflectance of the subjects. Incident metering does not depend on the subject, only the intensity of the lighting.
The Sunny 16 rule is based on the fact that the sun is equally bright everywhere outdoors between 10 am and 5 pm. So, if you know what the exposure is for sunlight at mid-day, then you can estimate it for cloudy or overcast situations.
The rule states that the proper exposure is determined by the ISO of the film/sensor setting. We will assume ISO 100. For ISO 100, at mid day with sunlit mid-toned object, set the aperture at f16, and the shutter speed at 1/ISO or 1/100th ( if your camera does not have a shutter speed of 1/100th, a setting of 1/125 if good enough for government work.)
Knowing this basic exposure allows us to draw up the following table based on exposure values. (To view and download a larger copy of this chart, click here.
Notice that the table shows values for ISO 100, 200, and 400. If you have ISO 1600, then f16 at 1/1600th is the correct exposure. Then, by equivalencies, the rest of the table can be constructed
But there are no consumer cameras with shutter speeds this high, so you will need to dial back the ISO in bright sunlight.
But, what if the day is not bright sunlight, but cloudy?? Then, the light is described by the shadows seen, or not seen.
Soft shadows, easily seen with soft edges is weak, hazy sunlight and needs 1 stop more light or f11 rather than f16 at 1/ISO.
Cloudy bright days refer to days where shadows are barely visible, and they require 2 stops more light or f8 and 1/ISO.
Overcast means NO SHADOWS and requires 3 stops more light or f5.6, the same as in the shade on a sunny day.
This knowledge can be very helpful.
One example that comes up frequently is people trying to shoot shots of the moon. They point their camera, in an automatic mode, at a black sky with a small, bright, white moon and find out that the moon is not exposed correctly at all.
The moon is a sun lit object - just like a car sitting on the street at noon - and the exposure should be very close to the same even though the moon is very distant.
So, for ISO 100 the setting would be f16 at 1/100th. Or we could open the aperture two f-stops (f16->f11->f8) and shorten the shutter speed up two stops (1/100th->1/200th ->1/400th) and shoot at:
Note the exposure data. Guess how I chose these settings???
... Just as predicted by the Sunny 16 rule. Now does this seem worthwhile to know??
Here is an image that is hard for meters do deal with - bright, sunlit snow. Indeed, I dialed in +1.33 Exposure compensation to help the meter read this scene.
EXIF data ->
Sunny 16 ->
This image is confusing at first, because f11 at 1/50th is two whole stops faster than required for a sunlit object. But the skier's faces are NOT SUNLIT, the faces are in the shade, and shaded objects require 3 stops more than sunlit. I actually only gave two stops more exposure due to the high reflectance from the surrounding snow. SO - shadowed subjects f11 ISO 100 1/50th is pretty good in the snow.
Here is another very brightly lit snow field at 1,000 feet - not a cloud in the sky.
EXIF data ->
Sunny 16 ->
Here is another image - shot in a cloudy day with barely visible shadows calling for 2 stops more light than bright sunshine at 7500 feet in Wyoming.
Sunny 16 -> (suggests two stops more light than sunshine)
Again - pretty close!!
Again, the horse's shadow is barely visible, shot at 7000 feet in Wyoming. Add two stops:
Sunny 16 ->
Again, it seems to work.
I hope I have demonstrated that the Sunny 16 rule is easy to understand and can be very helpful in understanding exposures needed and in interpreting your camera's exposures properly.
Discuss this tutorial or ask questions in this thread on Digital Grin!