What a busy, crazy month its been since I wrote about wanting to post photography fundamentals here on Travelomo.com. Sorry if I’ve kept you waiting, but here we go. I’d like to start out this series with a topic that befuddles many beginners: exposure.
Definition of Exposure
So, what is exposure? The definition of exposure, according to Wikipedia, is “the total amount of light allowed to fall on the photographic medium during the process of taking a photograph.” In simpler words, it’s the amount of light that hits your film to produce an image.
Three variables determine a photograph’s exposure. The first is aperture (which is just another word for “opening”). The second is shutter speed (the amount of time your camera lets in light). The third is ISO (the sensitivity of your film to light). The first two variables regulate the amount of light that enters a camera. The third determines how much light is needed to burn an image onto the recording medium (the higher the ISO, the less light needed for a shot). Understanding the relationship among these three variables is fundamental to our understanding of what exposure is and how to control it.
The Drinking Glass Analogy
There are several analogies used to illustrate this relationship, but my favorite is the one that uses a drinking glass, a faucet and some water. You can actually go and do this in real life, just to drive the point in.
The drinking glass represents a blank frame of film, while the water represents light. In order to create a photo, you have to fill that glass up by opening the tap and letting the water flow. Now, you can open the tap just a little bit to let the water drip out slowly. Or, you can open it wide to fill that glass up fast. The tap represents your first control, aperture. The second control is shutter speed, which is represented by the time you keep the faucet running. The third variable, ISO, is represented by the size of your glass. If ISO 50 is a huge Slurpee cup, ISO 800 is a shot glass. (more…)