There are some things every good photographer should know and "The Sunny f/16 Rule" is one of them. It is pretty simple, but it will help you get the right exposure on a sunny day. The basic idea is that on a sunny day, set your camera's aperture to f/16 and set the shutter speed to 1/ISO of the film you are using. For example, you are out taking pictures of "The Mittens" and there's not a cloud in the sky and you are using 100 ISO film. You can get a good exposure without any automatic settings by using an aperture of f/16 and a shutter speed of 1/100 or 1/125, whatever is the closest on your camera. This rule only applies to front lit subjects on a fully sunny day. If there are a few clouds and the sunlight is hazy then up the aperture to f/11. If there are many clouds, use f/8. If it is heavily overcast and there are no shadows, use f/5.6. This rule applies to both positive and negative film, but remember that negative film has a wider range of film latitude and is more lenient than slide film, where the right stop is more necessary.

Article by Jeremy Baker