Focus

When taking a picture photographers have to decide what they want the focus of the picture to be. This can be manipulated by using the focus, this is what you want to be clear in the photograph. If something is in focus then it is the clearest in the photograph and something that is out of focus is blurry.

Photographer: Cayusa

In some situations you might want everything in the picture to be in focus, like if you are taking a picture of a landscape and you want it to look the same way it does to the human eye. The aperture is the main way of controlling what is in and out of focus or if you are using the correct terminology depth of field. For this type of picture you will have to set a small aperture and begin by putting the ISO on the lowest setting to give the most amount of detail and the least amount of sound.

Sometimes you will want a shallow depth of field for a portrait. Using a wider aperture will make your picture more interesting to look at and will show the viewer the thing that you are wanting to focus on in that picture. this works best with a telephoto focal length lens because if you get too close to the subject you will reduce your depth of field.

After finding more out about focus I think it is a really important thing for photographers to learn about if they want to make impacting and more interesting photographs. 

Source:

http://www.digitalcameraworld.com/2012/10/01/best-camera-focus-techniques-10-surefire-ways-to-get-sharp-photos/