When a photo is taken by a camera the light from the outside pass through an iris or a diaphragm before it reach the light sensitive sensor inside the camera body. The size of the opening in the iris is refered to as aperture and is expressed in f-numbers or f-stops. F-stop is then abbreviated as f/1.8, f/11, f/22 and so forth.
The higher the f-stop value, the smaller the opening in the iris become and a lower value then give a bigger opening. The effect this has on the photo taken is that the smaller the opening is, the bigger is the area in the photo which will be in focus. In the photo below a very small f-stop was used which resulted in a photo where there is only a small point on the top of the nail which is in focus while the rest of the photo is blurry.
In the photo below we can see the opposite use, a big f-stop, used to get the entire length of the photo to remain in focus. When we speak of focus in this manor in our photographs this is often referred to as the Depth of Field.
- Aperture and shutter-speed is the two key factors which will help you get a photo with good exposure.