Exposure

Loosely an exposure is defined as the process of light entering the camera and forming an image on the lens/film.

Exposure is a term that is used widely in photography. An exposure is something which indicates that light is passing into the camera through the lens. Usually exposure is quantified by an other term depending on the quality of the photograph.

For example, one of the usages of exposure is in qualifying the image. Consider the set of photos below. Assuming that the photo in the center is how we want our image to look like, you can easily make out that the photo on the left is darker than desired and the photo on the right is brighter than desired. This means that less light than necessary entered the camera to form the image in the left case. Hence the photo was not exposed correctly, in this case the photo is 'under'-exposed. Similarly in the right photo, too much light found its was into the camera and hence the photo is 'over'-exposed. Since the photo in the center is what we need, we would say that this photo is exposed correctly.


So we have now come across the different exposure qualities. Lets say we consider the under-exposed photo. Why is the photo under-exposed? It could be because the shutter speed was too fast, or the aperture was too small or a combination of both. Similarly the over-exposed image was a result of the shutter speed being too slow, or the aperture being too wide or a combination of both. From either cases we realize that exposure is a resultant of the shutter speed and aperture. Exposure is directly proportional to aperture and inversely proportional to shutter speeds. This is the mathematical definition of exposure.

Mathematically,
Exposure = Aperture / Shutter Speed.
[Note: There might be other factors affecting exposure, but this is the relation of exposure with aperture and shutter speed]

To achieve good exposure one must choose an ideal combination of aperture and shutter speed. In the point-and-shoot mode, the camera itself has an automatic control mechanism where it would choose the aperture and shutter settings for correct exposure. In little more advanced cameras there is a shift mechanism whereby you can set an increase in shutter speed and corresponding decrease in aperture or a decrease in shutter speed and corresponding increase in aperture. You might wonder where is the necessity to modify the automatically chosen shutter and aperture settings. This part we will cover in the posts on how to get creative with aperture and shutter. For now its important to understand the relation of Exposure to Aperture and Shutter-speed.

The other usage of exposure is 'long'-exposure and 'short'-exposure. Long-exposure refers to taking a photo keeping a longer shutter speed duration while short-exposure is one where the shutter speed is very high. The reasons for long and short exposures will be looked at in the posts that deal with creativity.