calculated the power of my flash at different zoom length than the maximum, because the manufacturer only provides the guide number for the maximum zoom length lol (so it's more focused, more power looks better on a spec sheet). tested it and it works perfectly, I made a couple of cheat sheets for the two specific lengths I use the most (50mm and 105mm, one covers the entire frame and the other only the subject in the center, it's a style), i'm happy to have done that