I'd like to add that the smaller the aperture (the larger the f-number) you use the closer you'll get to the Diffraction Limit
of the camera. That is, in general, lenses get sharper as you stop them down (use a smaller aperture) until you reach the diffraction limit (generally f/16) when it starts getting softer again.
This is just to let you know that, as soon as you think you understand something, something else will jump up and bite you. Have a nice day.