I have had two or three of the Yongnuo 568 speedlites and use them with a Canon 24–70mm L lens on a Canon 5D MkIII and a 6D.

The problem I have on both is when I zoom in the power is not correct. If I shoot wide open the flash is perfect in E-TTL but if I zoom to say 50mm it gets darker, and if I zoom to 70mm it gets darker still. Is this a zoom issue? It happens on all three of my Yongnuo flashes and on both cameras. I will be delirious with glee if you can help... in the hope I don't have to revert back to Canon flashes.

All my Yongnuos act the same. Surely this cannot be a fault in all three. I am sure I am doing something wrong.

  • What metering mode is selected? – Michael C May 10 '18 at 0:32

All my Yongnuo's act the same..surely this cannot be a fault in all 3. I am sure I am doing something wrong.

Well, it kind of is a known issue with Yongnuo flashes when using Canon's Evaluative Metering.

Switching main metering to Center Weighted Average, Partial, or Spot metering modes and changing the menu item [Shooting (Red Tab with camera symbol) Tab 1→External Speedlite Control→ETTL II Flash Metering] from Evaluative to Average usually resolves the issue.

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  • Are you sure you don't mean TTL metering should be set to "average" rather than "evaluative"? AFAIK, metering pattern has no effect on TTL. – inkista May 14 '18 at 19:40
  • @inkista I usually change both. It works for me. – Michael C May 15 '18 at 21:53

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