Friday, July 22, 2011

The all-important, not-so-holy trinity of photography

For some of you, this will be old information, but hopefully for others this will be new. Either way, I hope this will help you understand a little more about photography and your camera.

At its most basic, photography is simply capturing light. The amount of light and the characteristics of the light determines how the photo will turn out. When you press the shutter release, the shutter opens allowing light to pour onto either the film or the image sensor. In this process, the camera uses three mechanisms to control the amount of light that is captured in a photograph: aperture, shutter speed, and ISO.

My Canon 40 D
 The aperture is the opening that lets light into the camera through the lens. The size of this opening can be made either larger or smaller to let in more or less light as needed. The size of the opening is denoted using f-numbers such as f/2.8, f/3.5, f/4, f/5.6, f/8, f/11, f/16, f/22 etc.... Although somewhat counterintuitive, smaller f-numbers indicate a larger opening. So, f/2.8 will let in a lot more light than f/22. Adjusting the aperture is also one of the primary ways to control the depth of field in a photo. Depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. A smaller f-number ( like f/2.8) will have a much shallower depth of field than a larger f-number (like f-22). I'm sure I will talk more about depth of field in another post to come. On my camera ( on the fully manual mode), the aperture is adjusted using the wheel on the back of the camera.

Wheel that adjusts aperture
The next mechanism that controls the amount of light is shutter speed. Shutter speed is the time the shutter remains open when taking a photo. Shutter speeds are denoted in terms of seconds such as 1/250th, 1/125th, 1/60th, and 1/30th of a second etc.... With the bulb setting, which is available on many cameras, you can keep the shutter open for minutes even hours. Obviously the longer the shutter remains open, the more light that will enter the camera. An important side note is that generally any shutter speed longer than 1/60th of a second will cause camera shake (resulting with blurry images) if you are holding the camera by hand. At this point it is usually smart to attach your camera to a tripod.  Though with a good image stabilizing system and a steady hand, you will probably be able to squeeze out a few more fractions of a second. Using shutter speed is one of the main ways to capture motion in photography. A fast shutter speed will freeze objects mid-motion, and a slow shutter speed will blur the objects motion. Once again, this is a topic I'm sure I'll discuss further in another post. On my camera, you adjust the shutter speed using a wheel that is jsut above the shutter release button.

Wheel that adjusts shutter speed

 The final mechanism is ISO, which is a measure of the film's ( or image senor's) sensitivity to light. These are denoted like ISO 100, 200, 400, 800, etc... The higher the number, the more sensitivity to light. Although, higher ISOs also result in more grain or image noise in a photo.. On my camera, the ISO is adjusted by pressing a button on the top of the camera and then turning one of the previously mentioned wheels ( I can never remember which).

ISO Adjustment
All these three things combine to control the amount of light that is captured. By increasing one and decreasing another, you  can let the same amount of light in but with different effects (different depth of field, more or less grain, etc..) This is about as much as I understand on the topic. If anyone has anything further to add, please post a comment.

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