Photography

Photography is the process of creating images based on light, usually using either electronic sensors or film emulsions (chemicals).

Exposure

Sensors do not work well with too much or too little light. Exposure is a term for the amount of light hitting the sensor and is also affected by the type of sensor.

Exposure triangle:

• Shutter speed (time the shutter is open)
• Aperture (size of the opening in the diaphragm in the lens. Large apertures let through more light)
• ISO (sensitivity of the film or electronic sensor to light)

  The Sunny 16 rule is a method for determining exposure without a light meter. Shutter speed should be around the inverse of the film ISO. If using ISO 100 film or something like Kodachrome 64, then, on a Sunny day, Shutter Speed 100, Aperture f/11. More cloudy go towards f/4. If sunny and on snow or sand, f/16. Modern film like Portra is quite tolerant of overexposure. It is possible to get decent images by guessing and experience.

Metering

Most modern cameras have built-in light meters to help determine the proper exposure.

Matrix metering

The computer evaluates multiple areas of the frame and calculates the optimum exposure.

Center-weighted metering

The computer gives greater importance to the center of the frame.

Spot metering

The computer meters based on a very small area in the center of the frame, or sometimes based on the autofocus point if that is not in the center. This depends on the specific camera.