Yesterday was a bright sunny day here in Portland and, being curious, I decided to check my meters against the "Sunny 16" rule. I used three different meters and three different methods: incident, reflected and spot. I went out into the yard at midday and took an incident reading in bright sun with the white dome held aloft and pointed back at the house. I also took a 1° spot meter reading from a grey card in the sun, and lastly I went back up on the porch and metered the yard where I had been standing with a Gossen Luna Pro F in reflected mode.

The result? All three meter readings were within 1/3 of a stop of each other (thank goodness), the average reading being EV 14. At ISO 100 this works out to 1/60 at f/16. The Sunny 16 rule for this ISO would indicate 1/100 at f/16, almost a full stop less. I realize Sunny 16 is a crude approximation, but many people swear by it.

So the question is, where did this rule come from? If my metering experiment is any indication, it should be "Sunny 11."

Jonathan