Digital Photography Techniques

Why the Sunny 16 Rule is still relevant

The Sunny 16 Rule allows you to set correct daylight exposures without the aid of a light meter. It uses a combination of observation and calculation to set the aperture and shutter speed. But why, when all modern digital cameras have an internal light meter and modes that set shutter speeds or apertures automatically, would I bother to estimate exposures for myself?

Two reasons:

  1. My digital camera has 30 buttons, dials, and knobs, many of which affect the exposure. I might change the ISO, have exposure compensation set, or accidentally have left bracketing turned on. If I know what exposure setting I should expect, I can tell if something is set wrong in my camera. Many times I have seen people in my workshops that have been shooting all their pictures at ISO 1600 and not even realized it. As soon as I handle their camera I can tell there is something wrong by knowing the Sunny 16 Rule.
  2. When I walk around with my camera, I like to have it set in the right range for a good exposure. That way, if a picture suddenly presents itself I can bring my camera to my eye and take a picture quickly. Because I am on or close to the right exposure, my second and third shots will only need minor adjustment and can be made quickly.

What is the Sunny 16 Rule?

In essence, the Sunny 16 Rule says that if you set your camera to f/16 on a sunny day, the shutter speed should be 1 divided by the ISO setting of your camera. So, if my ISO is 200 I should have my camera set to f/16 at 1/200 of a second. If you know equivalent exposures, you then know that you could also set your camera to f/11 at 1/400 of a second, etc. to get the same exposure. The f/16 setting is just your starting point.

The starting aperture that allows us to set the shutter speed to 1/ISO will change depending on the available light. The following chart shows how:

A sunny 16 kinda day!


Lighting Conditions 

Shadow Detail 





Slight Overcast

Soft around edges



Barely visible


Heavy Overcast

No shadows

Give it a try

Set your camera in manual and your ISO to something other than Auto (never use Auto ISO!) Then, whistling a happy tune, walk about outside and check the light for what kind of day it is. Maybe it is overcast, so set your aperture to f/8 and your speed to 1/ISO setting. I usually start out at ISO 200, because that is the base on my camera, so I would set f/8 at 1/200. Take a shot and check the results.

What is ISO?

ISO measures the sensitivity of your camera. The higher the number, the more sensitive your camera is to light. ISO 400 is twice as sensitive as ISO 200, meaning you only need half the light at ISO 400 as you do at ISO 200 to make the same exposure. For example:  at ISO 400 you could take a shot at 1/60 sec. that would have required a shutter speed of 1/30 sec. at ISO 200. Very handy, but there‚Äôs no such thing as a free lunch. The higher you set ISO, the more noise and loss of detail occurs.