580 EXII on my 5D Mk III

[02Nomad]

When I'm using flash (580 EXII) on my new 5D Mk III (it also happened on my 5D Mk II) in P mode with the flash and camera set to ETTL, all of my shots are at 1/60 and f/4. Am I missing something here? It doesn't seem to matter what the lighting is (bright or dim), but the result in dim light is a shot that less than optimally lit. Any help or suggestions will be most appreciated.

[diverhank]

What you are seeing is how the flash is supposed to work in P mode.  The camera will set the ISO to 400, speed to 1/60 and the largest possible f/stop, in your case f/4 (I could be wrong here, I never use P with flash so I'm assuming regarding the f/stop).  The rest it leaves it to the flash power output (ETTL).

Similarly, if you are in Av or Tv, the camera will assume that you want to use the flash as fill flash only and use ambient lighting.  For example, in Av mode, in low light the camera will set your Tv to something ridiculously slow, resulting in blurred pictures.

The recommended flash setting is to set the camera to M and you control both Av and Tv while letting the camera/flash do the rest.  In M you still can take advantage of the automatic features such as ISO (again camera sets to 400 unless you tell it otherwise) and ETTL.  Bottom line is in M, you have to set Av and Tv values and the camera/flash will do the rest and often beautifully, especially with what you got (I have the same combo plus another 600-EX RT).   In addition, you can bias the flash output to help the ETTL out.

[amfoto1]

Actually, in all three auto exposure modes (Av, Tv, and P) the flash in ETTL is treated as FILL. The camera sets exposure according to the ambient light and flash output is reduced by something like -1.7 stops. You can use the dial on the back of the flash to set some + Flash Exposure Compensation to boost just the flash... or you can use Exposure Compensation on the camera to boost the overall image brightness.

In Manual (M) mode the flash output is FULL. The camera treats the flash as the only light source, doesn't reduce it and ignores ambient light (but ambient light can still influence the image, more or less depending upon the various settings being used). Dialing FEC up or down on the flash or dialing Exposure Compensation up or down on the camera will alter the overall exposure.

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Alan Myers

San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM 

[diverhank]

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@amfoto1 wrote:

In Manual (M) mode the flash output is FULL. The camera treats the flash as the only light source, doesn't reduce it and ignores ambient light (but ambient light can still influence the image, more or less depending upon the various settings being used). 

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There are two kinds of M mode..one for the camera and one for the flash.  For the flash M mode, you are correct the output is full.  I was referring to the camera M mode with the flash set to ETTL.  Just a clarification for the OP.

[02Nomad · Accepted solution]

Thank you both for your replies! I'mgoing to have to just sit down and play with the camera and flash until I get what I want. When I was shooting film for weddings, I always had the flash on full and set the camera for 1/60 and the f stop anywhere between 5.6 and 11 depending on the situation. I guess that I was expecting too much from the setup that I was using... must have gotten lazy in my old age. Again, thank you gentlemen.