Aperture & Shutter Speed

Before light reaches the sensor, it must pass through the opening called the aperture. This can related to a human eye where light is let in through the iris depending on how much light we need to see, this is controlled on a camera by changing the f-number or f-stop value.

Exposure is all about different combinations of f-stop and shutter speed settings, these combinations can drastically affect the outcome. For example, the following three pictures have been taken with near enough the same amount of light, but the shutter speed and f-stop combinations make each one really quite different. I believe that blurring out a certain part of some images can enhance the aesthetic qualities of the image.





Left Image- F22:1/4
Middle Image- F8:1/30
Right Image- F2.8: 1/250


Although these images are small on this page, the background on the picture on the right is more blurred than the image on the left because the aperture is F2.8 which is a wide aperture which makes the objects further away from the subject are more out of focus. This is known as depth of field.
There is sometimes some confusion in relating the 'f number' with how big the entrance pupil in the lens opens. Basically the way that I remember is that the higher the f number, the smaller the hole and that the lower the f number, the bigger the hole where the light enters the lens. The image below shows how the higher the f number, the smaller the hole and visa versa.

If you take down the shutter speed 2 stops for example, you need to put the aperture up 2 stops to end up with the same exposure level.