Exposure: balancing ss and aperature

Now that you understand the mechanics of ss and aperature, let's apply them! There are numerous different combinations of shutter speed and f-stops which will result in the same amount of light exposure. If you change to a faster shutter speed that lets in half as much light, then you could maintain the same amount of light by opening up the aperature one stop to allow back in half again the amount of light. The reverse is also true; if you change to a slower shutter speed that allows in twice the amount of light, maintain the exposure balance by using the smaller aperature opening to cut the light in half.

Now here's the twist: although changing the shutter speeds and aperature settings will maintain the same amount of light exposure, they will change the effects in the actual photograph. These effects will yield different values for depth of field as well as the ability to stop the subject's action (think freezing time).

Depth of field. Look at a picture and notice that the foreground is generally blurred, becomes sharper focused around the subject, and then grows gradually blurred again. This is referring to the depth of field. I'll cover this more in detail in a later lesson, but here's a good overview. The smaller aperature openings produce a larger depth of field while the larger aperature openings produce the shorter depth of fields.

Stop Action. When photographing a moving subject, you need to use a faster shutter speed, beginning with 500. Remember to use a larger aperature opening to maintain the correct exposure. You will not get as much depth of field this way, but at least the subject will be frozen in timeinstead of blurry from moving too quickly.

Application. Before taking your photograph, evaluate the subject and the setting. Obviously if you're at a NASCAR race, you don't want the photo to be blurry and will set a higher shutter speed (probably 1000). Just don't forget to open up the aterture for the correct exposure balance. The meter will tell you this (covered in another lesson), but never get into the habit of relying on your equipment to tell you what to do.