Aperture

                                                                                                                          

this has both F2.8 & F16

we should relate the aperture to the eye.
the smaller the aperture, the larger the F-number , the higher the aperture, the smaller the F-stop.
the smaller the aperture affect's the depth of field by  making the focus sharper vs. with a smaller F-number it isolates the background and making it more blurry.