Understanding Proper Exposure
Over the years, the best analogy I've found to describe Proper Exposure is a full bucket of water. Using a garden hose will take a long time to fill the bucket. But using a fire hose will fill it in a fraction of a second. Same end result.
The Two Components of Proper Exposure
Aperture and Shutter Speed are the two camera components we'll discuss. Your Aperture is like the hose. Your Shutter Speed is the time it takes to fill the bucket of Proper Exposure. A small Aperture of F11, 16 or 22 will require a longer time (slower Shutter Speed) as opposed to a large Aperture of F1.4, 2 or 2.8 needing very little time (fast Shutter Speed) to get the Proper Exposure.
Each step in Aperture or Shutter Speed will halve or double the amount of light. For any given picture there are a number of combinations that will work. Shooting at 1/500 and F8 or 1/250 and F11 or 1/125 and F16 or 1/60 and F22 will all result in the same amount of light hitting the film. The difference will be in how much Depth of Field you get and how well action or movement will be stopped. It's up to you to decide which is best for the subject matter you are shooting.
I know that for some people this is heady stuff. It took me a while to understand it all. Once you get a good grasp of how Aperture and Shutter Speed change how your pictures look, you're on the way to creating images the way you see them in your minds eye. Be patient Grasshopper! It will all be clearer soon.
What's an Aperture?
Simply put, the Aperture is an opening in the back of the lens. It can be made big or small, letting in a lot of light or just a little. Depending on the lighting conditions you're shooting in, you or your camera adjust the Aperture. bright sun - small opening. Indoor, low light - big opening.
The size of the opening is referred to as an Fstop or F number. You'll see these noted as F2.8 or F5.6 or F16. Each step up or down the scale of F numbers will double or halve the amount of light coming through the lens. Contrary to what you may think, a smaller number is a bigger opening. The natural Fstop numbers are as follows:
1.4 / 2 / 2.8 / 4 / 5.6 / 8 / 11 / 16 / 22 / 32 / 45 (and so on)
The Aperture also controls Depth Of Field. DOF is the amount in front of and behind your focus point that will also be in focus. Smaller openings (F11,16,22) give more DOF; larger openings (F4,2.8,1.4) give shallow DOF. Controlling the Aperture allows you to intentionally blur the background or get a lot in focus from front to back.
What is Shutter Speed?
The second part of the Exposure combination is Shutter Speed. The shutter stays closed until you decide to mash the button. Then it opens for a fraction of a second (usually) to let the light hit the film or sensor and capture that magic moment in time.
If you remember from the previous few paragraphs, the Aperture controls how much light comes through the lens. The Shutter controls how long that light hits the film or sensor. Proper exposure = just the right combination of the two. As you might imagine, there are a number of combinations of Aperture and Shutter Speed that result in proper exposure.
Shutter Speeds are expressed as fractions of a second. When you see 15 or 60 or 250 in your viewfinder it's really 1/15th, 1/60th or 1/250th of a second. Exposure times of one second or more are normally indicated by the letter 'S' next to the number. 1s, 2s, 4s would indicate one, two or four full seconds.
Just as with Apertures, each step up and down the scale of shutter speeds will halve or double the amount of light. Shutter speeds are as follows:
1s, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000 and so on.
How do Shutter Speeds affect how your pictures look? They control how action and movement are recorded. Fast shutter Speeds (1/250, 1/500, 1/1000) will stop action. A golf swing, a tennis racket or baseball bat, a race car, or any other sport are times for using high Shutter Speeds. On the other hand, slow Shutter Speeds will blur movement. The most common use is for waterfalls and flowing water to get that smooth, milky look to the water.
How Does My Camera Know?
The light meter in your camera will (usually) give you the correct exposure. Depending on which exposure mode you've selected, or scene mode you're using, the aperture and shutter speed combination will be shifted accordingly. You can also, on most cameras, force the camera to under or over expose. Read the articles listed below in the Related Articles section to get a better handle on ways you can control your exposures.
Cameras today are quite sophisticated. Technological advances in metering systems have made exposure almost foolproof.
Almost. Someone keeps on inventing better fools!
