Certified Professional Photographer (CPP) Practice Exam

What does the equation E = IT stand for in photography?

1. Exposure equals Intensity times Time

2. Exposure equals Image time

3. Intensity equals Exposure divided by Time

4. Time equals Exposure divided by Intensity

The correct answer is: Exposure equals Intensity times Time

The equation E = IT is a fundamental relationship in photography that expresses how exposure (E) is determined by the intensity (I) of light and the duration of time (T) that the sensor or film is exposed to that light. This concept highlights the importance of balancing these three factors to achieve the desired exposure in an image. When you increase the intensity of light, such as by using a more powerful light source, you can either shorten the exposure time or maintain a shorter duration while still achieving the same exposure level. Conversely, if the intensity of light is lower, compensation can be made by increasing the exposure time to ensure that the sensor captures enough light to register a properly exposed image. This equation is essential for photographers to grasp because it informs decisions about camera settings, such as aperture, shutter speed, and ISO, influencing how images are captured in various lighting conditions. Understanding this relationship enables photographers to manipulate their environment effectively to produce quality photographs.