On the YN560 speedlight, the 'zoom' numbers range from 24 to 105. Just what do the numbers refer to in terms of flash emission? Is there any correlation between these numbers and the range of zoom lenses that say, range from 24mm to 105mm, or is it something else entirely? I know that this info. is covered in the 'manual' but it ithe info is confusing to me. Thanks. (P.S. This is not an endorsement or critique of this flash. I just want information). Thanks.