A couple Canon flash questions

I've had a couple things happen using Canon flash that I was wondering if anyone could shed some light on - no pun intended

1) Several times when using manual flash I have not been able to get the power low enough. 1/128 power was too bright, but if I switch to ETTL I can easily dial back the FEC and get the power low enough.

2) When shooting ETTL flash with manual camera exposure, if I change the aperture, to pickup more or les ambient light, or get more DOF, I figured that ETTL flash would adjust for that, but it does not, and I have to adjust the FEC and/or the ISO to compensate.

I'm probably just doing something wrong, or not understanding how these things should work. Any feedback would be appreciated.

1. It has been reported that in ETTL you can reduce power more than 1/128 using FEC.

2. How much of an adjustment? ETTL a good tool but in the end it is always ball park. It isolates your subject and gets information from light reflected back from said subject. That is why Canon provided FEC.

someone once mentioned that while M/128 is the lowest you could dial in, 1/256 is the lowest available under eTTL control.

As for ETTL I long ago stopped worrying about what is supposed to do. I just do whatever it takes to get the correct exposure. As for it evaluating reflected light it just works with the info it gets.

It isolates your subject so using a bride and groom as an example - a bride in a white dress will underexpose and a groom in a black tux will overexpose. Although it has nothing to do with cameras light meter the flashes exposure system works the same way.

Same as your camera shooting pure snow or pure black pavement. You need to compensate the exposure. If the frame has 50% snow and 50% pavement the exposure will be correct.

That is the flashes Evaluative mode that you can only access via the camera flash menus - if it has it. If it does there is an Average mode. This mode does not isolate the subject but averages out the entire scene. Some like to use it for indoor flash but it is not that good for outdoor shooting.

The best option is manual which I will always use first if I can. In a busy environment I will use ETTL and I chimp the histogram and exposure and FEC as needed.

KatManDEW wrote in post #18339982
2) When shooting ETTL flash with manual camera exposure, if I change the aperture, to pickup more or less ambient light, or get more DOF, I figured that ETTL flash would adjust for that, but it does not, and I have to adjust the FEC and/or the ISO to compensate.

Remember, ambient light metering is a separate function from eTTL flash metering, and one has no effect on the other. Let us assume that you measured a scene to find

Situation A:

• ambient: ISO 100 meters 1/100 f/5.6, so you change aperture to f/8 to let in less ambient light (summary: ambient exposure = -1EV)
  
• flash: ISO 100 eTTL, reads preflash at f/8 and emits flash to suit (summary: flash exposure = 0EV)
  

• ambient: ISO 100 meters 1/100 f/5.6, (summary: ambient exposure = 0EV)
  
• flash: ISO 100 eTTL, eTTL reads preflash at f/5.6 and commands flash to suit (summary: flash ambient = 0EV)
  

• ambient: ISO 100 meters 1/100 f/8 but your subject is 'darker than midtone', so you adjust to 1/100 f/5.6 (summary: ambient exposure = +1EV from metered reading)
  
• flash: ISO 100 eTTL, because you knew the darker-than-usual subject needs more flash than usual you set FEC = +1EV, eTTL reads the preflash and tells flash to put out +1EV of light (summary: flash ambient = 0EV)
  

1. the ambient brightness of exposure changed between each situation
   
2. the brightness of flash exposue remained the same between each situation
   

Thank you for the detailed explanation. That makes sense.

Thank you.

THank you. Now that you mention that I do think I may have heard that.

Thank you for that information.