An F-stop is an opening that lets the light go into your camera. You can change how much light goes into your picture by changing the F- stop numbers which is related to how big the opening of how much light goes in. F-stops are measurements of the aperture. An aperture is an opening that lets light get captured in your camera. The numbers of the different F-stops are confusing because they are backwards. For example , lets say that if we had an F-stop of F8 and F4 you would probally think that F4 has a smaller aperture. That is not true F8 has a smaller aperture than F4. In other words the larger the number the smaller the opening. What a F-stop does your picture is blurs out your background and focuses on one thing and the smaller the number the blurrier the background.
http://www.picturecorrect.com/tips/what-is-an-f-stop/
http://www.picturecorrect.com/tips/what-is-an-f-stop/
