Now I’ve tried to simplify these definitions but that is no easy task. Whole books are written in great detail about these terms. However, for now I am going to concentrate on remembering that all three of these directly relate to each other and work together to enable a photographer to capture images in creative ways. That said, I need to get lots of practice using different settings in each feature so I can begin to understand their relationships and power.
Next I am going to post about the different shooting modes.
ISO stands for International Standards Organization. It is the film’s sensitivity to light. The ISO lets your light meter know exactly what combinations of aperture and shutter speed it can use to record an exposure. The higher the ISO number is, the less light that is needed to make a picture. The lower the ISO number is, the more light that’s needed to make a picture. Higher ISO numbers can make the image grainier but it depends on what you want in your exposure. A higher ISO might be good if you want to freeze the action in sharply focused detail.
The shutter speed controls controls the duration of light. The length of time is the shutter speed and it is measured in seconds. 1/30 second, 1/250 second, 3 seconds, etc. On the T1i the shutter speeds range from 30 seconds to 1/4000 second when you shoot without the flash. There is another feature in the manual mode called bulb exposure. It lets the shutter stay open indefinitely as long as you press the shutter button. If you use the built-in flash, the fastest shutter speed in 1/200 second and the slowest ranges from 1/60 second to 30 seconds depending upon the exposure mode.
The aperture controls how wide the iris of the lens will open when you take a photo. A smaller f/number means a larger aperture opening, and the smaller fractions represent faster shutter speeds. These are called f-stops and an f-stop is a fraction that gives you the diameter of the aperture. The f stands for the focal length of the lens and the slash means divided by, and the number represents the stop in use. The aperture is a hole that lets light into the camera. You, the photographer can control how much light you let in. The aperture also affects the sharpness of your image. This is where depth of field comes into play. You decide just what you want in focus- everything or just one part of the image.