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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 01 Apr 2014 (Tuesday) 18:43
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ETTL issues when using multiple 600EXRT setup with on camera flash

 
pstyle1
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Apr 01, 2014 18:43 |  #1

Ok, so hopefully someone here can help or give insight.

I'm encountering issues with this set-up:

2 600EX RT's set up on stands, and 1 600EX RT on camera.

When the 2 off camera flashes are behind the subject, the on camera flash underexposes when in a bounce position (works ok when straight on). Camera is in M mode. This was tested with a low, white ceiling.

I've tried this in both full ETTL on all flashes (in group mode), as well as setting the off camera flashes on M and dialing them way down and leaving the on camera flash on ETTL. I'm guessing the camera meter is seeing the bright flashes behind the subject as a well exposed scene and thus will not give a lot of fill? I've tried both spot and matrix metering with similar results.

The idea is to create rim/side light, while the subject is correctly exposed, and turning off and on various flashes as needed. This is all in Group mode. I want to use this type of lighting for wedding receptions.

Another issue I'm encountering, is when in group mode, if I turn off the OCF's (from the flash menu), the on camera flash won't fire, even if it's set to fire. I will have to take the flash out of group for it to fire.

Hope this all makes sense!


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The ­ Loft ­ Studios
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Apr 01, 2014 19:06 |  #2

pstyle1 wrote in post #16802650 (external link)
I'm guessing the camera meter is seeing the bright flashes behind the subject as a well exposed scene and thus will not give a lot of fill? I've tried both spot and matrix metering with similar results.

This is correct…..
The bright rim lights are telling the camera, "Hey there's a lot of light in this scene…" Thus shutting off the On-Camera Flash which leads to an underexposed image. Upping the Exposure Comp on the On-Camera Flash to say a +1 or +2 may help…..

pstyle1 wrote in post #16802650 (external link)
The idea is to create rim/side light, while the subject is correctly exposed, and turning off and on various flashes as needed. This is all in Group mode. I want to use this type of lighting for wedding receptions.

At my Wedding Receptions, what I do is set the two OCF to Manual, (Left side Group-B / Right Side Group C) then meter my exposure towards the middle of the dance floor (For Example, let's say ISO 1600 @ f/2.0). Then set my On-Camera Flash (Group A) to E-TTL… Camera is in Manual Mode at ISO 1600 Shutter between 1/30 - 1/200 @ f2.8 (My shutter range is so, depending on the amount of ambient I want to let in). Now, you can still shut off which individual Groups you want or keep them all on…..

pstyle1 wrote in post #16802650 (external link)
Another issue I'm encountering, is when in group mode, if I turn off the OCF's (from the flash menu), the on camera flash won't fire, even if it's set to fire. I will have to take the flash out of group for it to fire.

Never had this experience…..


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pstyle1
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Apr 01, 2014 19:25 |  #3

How do you assign a group to the on camera flash? It's not obvious to me just looking at the back lcd of the flash. I just make sure the little flash symbol is on so it will fire.


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CliveyBoy
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Apr 01, 2014 20:13 |  #4

The on-camera flash adopts Group A settings. So, to set a ratio, the on-stand flashes should be in group B,

In the camera's flash control menus, set Wireless = Enabled, Firing Group = A:B, and A:B ratio to something like 2:1, then test and adjust.


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The ­ Loft ­ Studios
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Apr 01, 2014 20:28 |  #5

pstyle1 wrote in post #16802756 (external link)
How do you assign a group to the on camera flash? It's not obvious to me just looking at the back lcd of the flash. I just make sure the little flash symbol is on so it will fire.

The On-Camera Flash is automatically set as Group A.....


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pstyle1
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Apr 01, 2014 21:42 |  #6

The Loft Studios wrote in post #16802867 (external link)
The On-Camera Flash is automatically set as Group A.....

Ah.. thanks for that! That's why the on camera flash kept turning off when I turned my Group A OCF off! Learned something new! Thanks again!


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pstyle1
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Apr 01, 2014 21:46 |  #7

aaaand that took care of my under exposure issue.. DUH! I didn't know the on camera flash was automatically set to Group A, so when I had my Group A on manual power at 1/64th, the on camera was also on M!

I was scratching my head for way too long over that one.

I owe you a beer next time I'm in Houston!


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dmward
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Apr 01, 2014 21:57 |  #8

I use Gr mode exclusively at wedding receptions.
On camera is Gr A usually set to -1 or more EV ETTL
One off camera 600EX-RT in Gr B set to -2/3 EV ETTL
Other off camera 600EX-RT to Gr C set to 0 EV ETTL

Works like a charm. I usually have the camera set in M to about -1 1/2 to -2 EV.

The result is:

IMAGE: http://www.dmwfotos.com/weddings/galleries/sharronryan/photos/20130316DMWB0886-SR.jpg

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ETTL issues when using multiple 600EXRT setup with on camera flash
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