Speedlite 580 Exii with diffuser

[jdharford]

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.

[jrhoffman75]

The 430EX-III comes with a bounce diffuser. The manual warns that under exposure can occur because the guide number is reduced. 

[kvbarkley]

I am talking about this note:

"Even if you disable the built-in flash from firing, it will still fire in order to control the slave unit via optical transmission. The flash fired to control the slave may therefore appear in the picture depending on shooting conditions"

[jdharford]

Thanks to everyone for the comments.  To clarify, I was using the 580EXii with a 100mm macro lens with the camera on manual settiings and, for the test, shooting at one of my prints about 6 to 8 feet away.  Ambient light was too low to be a factor.  THe settings were at an intermediate f-stop and with the time around 1/60 second.   It did not seem that power limitations were the problem.  I was beginning to think that the pre-flash came from a different part of the flash than the exposure flash, but that does not seem to be the answer.  I tried the experiment with two different kind of diffusers, one which is a designed to bounce the light, and the other just a milky fitting on the flash head, but the results were much the same: the loss of more than a stop of exposure with the diffuser. I should probably try the same experiment with a lens set around 50mm. 

 Thanks again to all.

[RobertTheFat]

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@jdharford wrote:

Thanks to everyone for the comments.  To clarify, I was using the 580EXii with a 100mm macro lens with the camera on manual settiings and, for the test, shooting at one of my prints about 6 to 8 feet away.  Ambient light was too low to be a factor.  THe settings were at an intermediate f-stop and with the time around 1/60 second.   It did not seem that power limitations were the problem.  I was beginning to think that the pre-flash came from a different part of the flash than the exposure flash, but that does not seem to be the answer.  I tried the experiment with two different kind of diffusers, one which is a designed to bounce the light, and the other just a milky fitting on the flash head, but the results were much the same: the loss of more than a stop of exposure with the diffuser. I should probably try the same experiment with a lens set around 50mm. 

 Thanks again to all.

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In my experience, E-TTL is nearly useless when ambient light is not a factor. E-TTL is exceedingly averse to blown highlights and therefore exposes for the brightest elements in the scene. In effect, it takes the attitude that all flash is fill flash. If you don't have enough ambient light to support that notion, there are two alternatives: bounce flash or manual (not E-TTL) flash. Otherwise, underexposure, sometimes severe underexposure, is practically guaranteed.

[Waddizzle]

This sounds like an excellent scenario where a good light meter will guide you to good exposure.

[digital]

ETTL is a geat tool but ball park. I have seen this conversation many times. I long ago stopped trying to figure out why it will or won't copensate for a diffuser even if it is suppsed to. I just do what needs to be done to get the shot.