There seems to be a lot of confusion among both amateur photography that among professionals about the concept of "depth of field." Many people know that this is a concept closely related to the "fire" 's image. But beyond this there seems to be some kind of magic that seems harder to understand.
In reality the concept of "depth of field" is very simple and can be explained by using some pictures and explanatory graphics.
In a way ...

Have you ever wanted to experiment with macro photography, but do not have the budget to buy a lens suitable?
In this video, in English, Jim ProPhotolife shows a little trick to get a 1:1 magnification using two lenses.

Focus, in photo, is not just make the subject clear or be able to clearly see the elements in the image.
The focus may enhance portions of an image, make it penetrable by the viewer and create an emotional connection with this' last.
No matter what your ideal type of photography, the correct focus can help you greatly improve the quality (and not just technical) of your images.