If you have your Canon 7D set to Auto-ISO and you slip your flash on, whether it’s a Canon flash or a third party flash, like Metz… What are the rules for the Auto-ISO? That will depend on the mode:

  1. Tv or Av or P or CA or Full Auto: The ISO speed will be set at ISO 400
  2. Av Fill-in Flash: If the pre-flash detects over-exposure at ISO 400, then the ISO will drop to as low as ISO 100.
  3. P or CA or Full Auto & bounce flash: The ISO speed will be set between ISO 400 to ISO 1600 depending on the pre-flash.