Depth of Field

Depth of field is the amount of space in front of or behind an object, that appears to be in focus. Image format size also affects the depth of field. When focusing in the depth of field everything in front and behind the focus point become less sharp and more blurred.

f/8.o f/5.6 f/2.8
Focal length does not affect depth of field, it is used to make the image bigger or smaller which will blur the image if you get to close.