Understanding Your Equipment: Part 2 - Equivalent Exposures
On to Part 2. In Part 1 of the Understanding Your Equipment series we talked about the 3 elements of exposure individually. Now we're going to learn how they work together collectively.
For every exposure, there are multiple combinations of aperture, shutter speed, and ISO that will give you that same correct exposure. When I say exposure I'm talking about the amount of light coming into the camera. The aperture will be getting smaller therefore your depth of field will change BUT to compensate for the same amount of light I need to slow down my shutter speed to let in more light. Always remember that when you move in one direction on your aperture's scale you have to move in the opposite direction on your shutter speed's scale to keep the same exposure. In order the achieve this YOU MUST BE USING YOUR SCALES PROPORTIONALLY. For example, if you bring your aperture down one third of a stop you must be slowing down your shutter speed one third of a stop.
So, in this example, I took the first picture at ISO 100, f1.4, with a shutter speed of 1/1000 sec. I'm going to leave my ISO the same and change the aperture and shutter speed. As the number of the aperture gets bigger, I'm going to have to slow down my shutter speed to compensate the amount of light coming in to maintain the same exposure. Watch the numbers in this example and the depth of field as well:
The aperture chart below shows what stops are full stops and in between. If you go from f2.8 to f4 that would be a full stop but if you jump from f3.2 to f4 that would be two thirds of a stop and etc.
The same stop method applies to shutter speed and ISO as well. This chart shows shutter speed and aperture together proportionally as it would be in the camera. So like I said before, when one number goes up the other one goes down to compensate for the exposure.
This chart shows aperture and ISO together. As the aperture gets smaller (remember that means the number gets bigger) the ISO increases proportionally.
That's it! Those are the 3 elements of exposure, how they work separately and how they work together. I know its a lot to take in but practice makes perfect and the only way to know these by heart is to practice, practice, practice! The next part of the series is going to start on flashes. Please comment or email me if you have questions or comments about this post or even part 1.