I bought an Altura flash for my canon 60D which has settings from 24-105mm. However, my canon lens goes from 18-135mm. I'm not sure if my lens will couple at the flash settings or, do I just ignore the 6mm difference on bottom and the 30mm difference at the top? Also, the Altura manual is not too specific on how to set the mm setting; Do I set it for the 105mm or the 24mm with this lens? Any help will be greatly appreciated.