Panning+Zooming. Lighting Ratios and Incident Metering Demystified. The term "lighting ratio" is a quantitative measure of the difference between two light sources, or the amount of light reflection from the highlight and shadow sides of the face.
A numerical ratio is like a blueprint a builder can follow to construct a building he has never before seen. For example an assistant might be told to set up the studio lights for a "3:1" ratio and know per the convention for portraits that means the key light must be 2x (1 f/stop) brighter than the fill. What makes ratios and metering confusing for a beginner is the fact that there are two types of ratios, incident and reflected and an incident meter is used to infer the amount of light reflected from the face. To help clarify the situation let's start with a basic physics lesson: Joe McNally. Joe McNally's Blog. We celebrated Earth Day this past week.
This observance has been around for a while now, and back in the 70′s I was occasionally assigned to cover some of the events. I shot the above for UPI one year, at an Earth Day observance at the UN.