My 580 EX II exposes properly when the diffuser is not on the flash. The diffuser is made for this Speedlite and yet when I use it there is a drop in the exposure by about one and a half stops. I have tried the flash with different manual settings on the camera, and the result is as indicated. Changes in the manual settings without the diffuser were properly adjusted for and properly exposed, but the diffuser seemed to cause some problem. The setting in these cases is ETTL.
My 580 EX II exposes properly when the diffuser is not on the flash. The diffuser is made for this Speedlite and yet when I use it there is a drop in the exposure by about one and a half stops. I have tried the flash with different manual settings on the camera, and the result is as indicated. Changes in the manual settings without the diffuser were properly adjusted for and properly exposed, but the diffuser seemed to cause some problem. The setting in these cases is ETTL.
Why not simply use about one and a half stops of flash exposure compensation when using the diffuser?
That is, of course, a practical answer. But it troubles me that I do not know why an ETTL setting should not already compensate.
Unless you are talking about the built-in pull out diffuser panels how is the flash supposed to know there is a diffuser attached and that it needs to give more power to compensate for its output being diffused?
Because of the ETTL pre-flash - which is the whole point of ETTL. I doubt that he is putting the diffuser on in the instant between the pre-flash and the exposure flash!
Right, E-TTL should compensate. But, perhaps the distance is now too great compared to the reduced light output.
E-TTL is a tool not magic. Like any other automation on the camera sometimes it requires user input. Otherwise everyone should just be shooting on Green Square Auto.
This is a wild shot, but try using second curtain sync. It might be the preflash is interfering with the main flash. Canon uses some wierd language about this point in the manuals - though it is usually in reference to wireless flash.
