There is a handy rule of thumb that gives you a good exposure to use on bright sunny days. If your light meter breaks, this can save you! It is useful even when your meter is working. It's called "The Sunny 16 Rule," and it works like this.
On a sunny day when the sun is high in the sky, the correct exposure to use is f/16 with a shutter speed of 1/(the ISO rating of your film). For example, if you have 1000 speed film in your camera, you'll get a good exposure shooting at 1/1000 second at f/16. With 100 speed film, shoot at 1/100 second at f/16. (In practice you'd shoot at 1/125 second at f/16, because your camera probably doesn't have a 1/100 setting.)
Of course, any equivalent exposure to the Sunny 16 recommendation will work just as well. If Sunny 16 tells you to shoot at 1/125 at f/16, you can equally well shoot at 1/60 at f/22, 1/250 at f/11, 1/500 at f/8, and so forth.
Why is this exposure guideline valuable? It can help you with tricky lighting situations. If you are photographing a distant tree in a shaft of sunlight against a dark forest background, say, your light meter may get badly fooled. Sensing all that darkness, the meter will call for greater exposure in an attempt to lighten it up, resulting in a grossly overexposed tree. Sunny 16 saves you from this, since the tree is in direct sun and the rule will give you its correct exposure, leaving the dark forest appropriately dark.
Even before leaving the house, the rule is helpful to decide what film to load in your camera. Based on what f-stops you anticipate shooting at and what shutter speeds you want to be dealing with, Sunny 16 advises you on what ISO to load into your camera. If you want to shoot a sporting event with large depth of field, for example, it wouldn't make sense to load ISO 50 film in your camera. (Sunny 16 says f/16 at 1/60 or f/22 at 1/30, too slow to shoot sports when the lens is stopped down for depth of field.) Knowing what film to load is handy even if you have a totally automatic camera.
Sunny 16 can be extended into other situations as well. If the day is cloudy with a light overcast, add a stop of exposure to the Sunny 16 recommendation. If it's a heavy overcast, add two stops. If it's a sunny day but your subject is in open shade, add three stops.
Timothy Edberg / 6511 Homestake Dr. South / Bowie, MD
(301) 809-5857 / 1-877-471-6414 (toll-free)