Aperture and Depth of field
As a photographer I cannot emphasize the importance of having a good sense of knowledge of how Aperture and depth of field are related.
In a previous article (F-Stop is NOT an F-word) I explained the nomenclature commonly used for aperture is f-stop. Aperture and f-stop relate to the size of the lens opening.
As one of the three components of an exposure (shutter speed, lens aperture, ISO) aperture plays a vital role.
The primary use of aperture is to control the depth of field (the distance in front and behind the subject that is in apparent focus) of a photograph as well as in part control the amount of light that is allowed to enter the camera through the lens.
Also from the article (F-Stop is NOT an F-word) we discussed that the bigger the aperture/f-number is the smaller the opening which in turn results in a larger depth of field. If you were to set your lens to its biggest number the lens would be “fully stopped down”. Conversely, if you were to set your lens to its smallest number the lens would be “wide open”.
Now, having said all that let me also say the depth of field is not sharpness. What I mean by this is that just because you have a large depth of field it doesn’t mean that the subject will be sharp.
Apparent sharpness can be influenced by factors that have nothing or little to do with depth of field, such as lens quality, dirty sensor or lens element, fog or haze in the environment, even down to camera shake during long exposures.
So if you want good separation of your subject from the back ground set your aperture to a smaller number. Then, continue to adjust your aperture up or down until you get the desired results.
Below is a diagram showing the comparative size of full f-stop apertures.
As you can see from the below image series aperture is a powerful tool in your photographic arsenal. This photo shot with Canons EF 70 – 200mm f/2.8L IS USM lens.