The f Stop on a lens or aperture setting represents how wide the lens aperture is open. The smaller the f stop, (2.8 or 4.0), the larger the lens aperture. The larger the f stop, (11, 16, or 20), the smaller the lens aperture. Once again the aperture can be likened to the iris of your eye, the smaller the aperture or iris, the less light that is allowed to enter. The larger the aperture or iris, the more light that is allowed to enter.
The aperture has another effect other than controlling the amount of light that is entering into the camera body. The size of the aperture also affects the Depth of Field, (DOF), as well. The DOF is just that, the depth of area that is in focus. A shallow DOF will give a shallow area that is in focus. For example, you may recall seeing photo’s that the background and foreground is blurred to some extent but the subject is in tack sharp focus. This is a shallow depth of field. Conversely a DOF that has great depth to it, (is not shallow), will have the subject in focus as well as the background and the foreground. This is achieved through the f stop, (or aperture setting), with a large aperture producing a shallow DOF and a small aperture producing a deeper DOF. If you are using a zoom lens there will be another contributing factor to the DOF, and that is that of the zoom factor of the lens. To increase the bokeh, (blurred), effect, zoom the lens to it’s maximum zoom capability. To reduce the bokeh, (blur effect), reduce the zoom of the lens to it’s minimum zoom capability.
Understanding the relationship between your f stop, (aperture setting), and the shutter speed is very important. Let’s say we take a photo with an f stop of 8 and a shutter speed of 1/500 of a second to get a properly exposed photograph. We decide that we want to change our f stop to 3.5, (increase our aperture size), in order to get a greater blur effect in the background. What are we going to have to do with our shutter speed to compensate for the change in our f stop? Let’s think this through. We are reducing our f stop from 8.0 to 3.5, therefore increasing our aperture which will let in MORE light to our camera. If we do not adjust our shutter speed the photo will be over exposed, (too bright). This means we have to reduce the light entering the camera using our shutter speed to maintain proper exposure. Therefore increasing our shutter speed will compensate for the increased aperture. Next week we will discuss stops, and how to calculate these changes precisely in our heads!