600EX-II exposure question...help!

[CapeCodDan]

Using this strobe on a 6DMII. As I understand it, the ETTL mode works well only when the camera mode is set to P.  However, P tends to set the aperture to 4.0; when I need more depth of field, I have to use AV mode.  Now in order to get auto exposure out of the flash - so I can walk around shooting different subjects in different rooms, say - I switch the flash mode to Ext.A. (I think I'm doing everything right so far, yes?)  However this is tending to underexpose by at least two stops, so I adjust the flash's exposure compensation accordingly, to, say, +2....which I arrive at by trial and error.  My question is: is this the way it's all supposed to work?   Why aren't I achieving properly exposed images without having to compensate?

[MikeSowsun]

Your understanding of ETTL is incorrect. 

Ext.A is old school Film Era Thyristor flash using an External sensor on the front of the flash instead of the sensor inside the camera behind the lens. (TTL mean Through The Lens) . 

Most people will agree that ETTL flash is superior to External Auto. Do not use External metering unless you have a reason to use it, and know why you are using it.

My advice is to leave  the flash in ETTL and use Manual mode on the camera to select the shutter speed and aperture. Flash Exposure Compensation can be used to fine tune your exposure. 

[Waddizzle]

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@CapeCodDan wrote:

Using this strobe on a 6DMII. As I understand it, the ETTL mode works well only when the camera mode is set to P.  However, P tends to set the aperture to 4.0; when I need more depth of field, I have to use AV mode.  Now in order to get auto exposure out of the flash - so I can walk around shooting different subjects in different rooms, say - I switch the flash mode to Ext.A. (I think I'm doing everything right so far, yes?)  However this is tending to underexpose by at least two stops, so I adjust the flash's exposure compensation accordingly, to, say, +2....which I arrive at by trial and error.  My question is: is this the way it's all supposed to work?   Why aren't I achieving properly exposed images without having to compensate?

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What's shutter speeds are you trying to use?  Is this your first experience with a speedlight?  

I would use an on-camera flash with the camera set to Av or M modes.  I would set the camera and the flash to E-TTL.  I would use Av mode when I wanted the flash to be the primary source of light.  I would use M mode when I wanted the flash to be a secondary fill light by introducing negative flash exposure compensation.  .

[RexGig]

I have never used P, for anything, and my four 600EX-RT Speedlites work very well. I have normally used E-TTL, with the camera set to M, and have dialed a bit of FEC as needed. When I have dialed the FEC, it has normally been downward, when shooting at close range.

Canon E-TTL is usually accurate, in my experience, with the camera set to Manual. That way, I choose the exact aperture and shutter speed I desire.

I used 580EX, 580EX II, and 600EX-RT Speedlites, from 2010 to 2018, as part of my job, at night, so I have plenty of practical experience. The images were for official purposes*, so had to be done right. My wife taught me to use powerful Nikon SB-800 Speedlights, from the beginning of my DSLR experience. Syl Arena and Christopher Duncan taught me to use Canon Speedlites. These factors do not make me an expert, but should establish that I am not a beginner.

It is not difficult to set flash manually, as I do when using my secondary and tertiary systems.

*I photographed crime scenes, and crime victims, during the final part of my police patrol career.

[RexGig]

I should add that FEC = Flash Exposure Compensation. This is very easily done on 7D, 7D II, and 5D-series cameras. The 6D series has a different control set, with which I am not familiar.

I should also add hat my may is a way, not the only way.

[Waddizzle]

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@RexGig wrote:

I should add that FEC = Flash Exposure Compensation. This is very easily done on 7D, 7D II, and 5D-series cameras. The 6D series has a different control set, with which I am not familiar.

I should also add hat my may is a way, not the only way.

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The differences between different camera bodies is easily reconciled by using Custom Control programming.  I use the same buttons on a 6D, a 7D2, and a 1D4 for the same functions, including the rear dial and [SET] button.  All of the buttons within reach of the button function the same way.  

I do not use the joystick for changing the AF point.  That takes too long.  I'd rather reset the active AF point back to my default AF point, which I can do by clicking the joystick.  But, I program the {AF-ON] button to be {AF-OFF], which can reset the AF point to the center AF point, too.

With the advanced AF tracking in current cameras with all AF points enabled, I think makes moving your AF point around a thing of the past.  For example, I can reset the AF, focus with the center AF point, and recompose the shot while AI Servo tracking stays on the original focus subject.

[MikeSowsun]

You guys are all missing what the original poster said:

"Using this strobe on a 6DMII. As I understand it, the ETTL mode works well only when the camera mode is set to P.  However, P tends to set the aperture to 4.0; when I need more depth of field, I have to use AV mode.  Now in order to get auto exposure out of the flash - so I can walk around shooting different subjects in different rooms, say - I switch the flash mode to Ext.A. (I think I'm doing everything right so far, yes?)  However this is tending to underexpose by at least two stops, so I adjust the flash's exposure compensation accordingly, to, say, +2....which I arrive at by trial and error.  My question is: is this the way it's all supposed to work?   Why aren't I achieving properly exposed images without having to compensate?"

For some reason he thinks he has to switch the flash to External Metering Mode in order to use Av mode. It is External Metering Mode that seems to be causing his problems. He needs to switch back to ETTL mode.   

[Waddizzle]

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@MikeSowsun wrote:

You guys are all missing what the original poster said:

"Using this strobe on a 6DMII. As I understand it, the ETTL mode works well only when the camera mode is set to P.  However, P tends to set the aperture to 4.0; when I need more depth of field, I have to use AV mode.  Now in order to get auto exposure out of the flash - so I can walk around shooting different subjects in different rooms, say - I switch the flash mode to Ext.A. (I think I'm doing everything right so far, yes?)  However this is tending to underexpose by at least two stops, so I adjust the flash's exposure compensation accordingly, to, say, +2....which I arrive at by trial and error.  My question is: is this the way it's all supposed to work?   Why aren't I achieving properly exposed images without having to compensate?"

For some reason he thinks he has to switch the flash to External Metering Mode in order to use Av mode. It is External Metering Mode that seems to be causing his problems. He needs to switch back to E-TTL mode.   

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I had thought I had said that E-TTL mode needs to be used, either in Av or M modes.  Which mode to use depends on what it is that you need to light up.  The basic rule of thumb says shutter speed captures ambient light, while aperture setting captures the light from the strobe.

[MikeSowsun]

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@Waddizzle wrote:

I had thought I had said that E-TTL mode needs to be used, either in Av or M modes.  Which mode to use depends on what it is that you need to light up.  The basic rule of thumb says shutter speed captures ambient light, while aperture setting captures the light from the strobe.

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    You did say to use ETTL. I guess I missed that.  I am still curious to hear why the OP was using Extenal Mode instead of ETTL.

[RobertTheFat]

It's important to remember that ETTL tends to treat all flash as fill flash. So if you can't expose for the ambient light, only the highlights will be sufficiently exposed. One way to combat that is to use bounce flash; another is to let the flash unit, rather than the camera, decide how much flash power is required. I don't think the Canon manuals explain that particularly well; but I've owned several ETTL cameras, and it's worked that way on all of them.