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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 15 Jul 2011 (Friday) 08:22
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How many stops should a shoot through umbrella use up?

 
Dustin ­ Mustangs
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Jul 15, 2011 08:22 |  #1

I got an off camera flash setup finally and am a little disappointed with the flash power I am getting with a shoot through umbrella. I was taking some test shots of some camera gear on a dark wood table and I couldn't get a proper exposure. I was using a 430 exii with a shoot through about 3 feet from the subject. Even with the flash on full power and settings of 1/40, f4.5, and iso 800 they were still coming out under exposed. I finally bounced it unmodified off a standard height ceiling and got a proper exposure at 1/125, f8, iso 200 at iirc 1/2 power.

Does a shoot through umbrella really rob me of that much power? I am wondering if I was using it wrong or got the wrong one?? It isn't a dedicated shoot through, it is one of those removable cover ones (43" westcott). Does that make a difference? What zoom setting should I use and how far up the shaft should it be mounted?

Thanks for any help with this...

:confused:


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bobbyz
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Jul 15, 2011 08:27 |  #2

ISO800 at full power and 3 feet, sure your flash is ON?

And pictures always help a lot more than describing the problem. Take a shot of the setup and the subject and post it if possible. The umbrella shouldn't eat more than 1 to 1&1/2 stops I am just guessing.


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Jonathan12uiz
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Jul 15, 2011 08:28 |  #3

did you try using a light meter to see what settings the meter recommends for the setup you have?




  
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-MasterChief-
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Jul 15, 2011 08:29 |  #4

how are you triggering the flash?




  
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CiM_Photography
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Jul 15, 2011 08:30 |  #5

I've got to ask some basic questions, since the problem here is clearly an easy fix.
1: How are you triggering the flash?
2: Did you remove the cover on the shoot-through?
3: Are you shooting M, Av or Tv?

Let us know.


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Dustin ­ Mustangs
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Jul 15, 2011 08:36 |  #6

My new 60d has built in wireless and the flash was firing, external only, black cover was removed. Manual mode for exposure, ettl for flash. Ettl was maybe my mistake but I am pretty sure the flash was maxed out because increasing the flash exposure compensation had no effect.

I don't have a light meter to use and can't upload sample photos at this time...


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CiM_Photography
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Jul 15, 2011 08:45 |  #7

If you didn't have line-of-site between your 60D and your 430exII, it's possible that the e-ttl wasn't fuctioning fully/at all?

A 1/40th exposure time with an iso of 800 might have actually been enough to expose for ambient... so it's possible your flash wasn't firing at all. Remove the umbrella and all of a sudden it's functioning... that points to line of site issues.


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KaBlookie
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Jul 15, 2011 08:52 |  #8

Yeah, I'd verify it's actually firing, then put the flash in manual mode and at 1/1 power, just so you're 100% sure it's actually firing at full power.


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Dustin ­ Mustangs
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Jul 15, 2011 08:59 |  #9

It was deff firing, it was right next to my head and I could see the flash out of the corner of my eye. I will reproduce the shoot using manual flash control to see if I get the same results. Thanks for the quick replies on this, it is comforting to know the umbrella isn't responsible for this as I first had thought.


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dmward
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Jul 15, 2011 08:59 |  #10

Put flash on manual, if a 430 will permit that, and put a white paper towel on the table.
Make an exposure at 1/2 power on the flash at ISO400 F8 if the blinkies do not show on the camera LCD indicating clipping on the white towel increase exposure by upping ISO to 800 if the blinkies show up decrease exposure by 1/3 stop by closing lens down. If blinkies are gone that is your optimum exposure.

Remember that the TTL meter reading in the camera is trying to make the table medium gray. i.e. over exposed. could be as much as 3 or more stops.

Its likely the reason it seemed to work with bounce off ceiling is because the ceiling reflected in the table helping to make it reach mid gray for the TTL metering.


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nathancarter
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Jul 15, 2011 11:18 |  #11

I'm also using a 60D and 430EXII.

In a situation where I have plenty of time to experiment and test, I turn off ETTL and just go for manual flash control. I haven't found ETTL to be particularly reliable when using any modifiers. It works pretty well when I have just the bare Speedlite with no modifiers.

I like being able to assign flash ETTL compensation to the rear button, though. To change manual flash power you have to dig down into the menu each time... just a few extra button clicks, but still a bit of hassle.


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nes_matt
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Jul 15, 2011 15:41 |  #12

sure the lens cap was off? BTW, lengthening exposure time with flash exposure won't really help your subject exposure. Unless you are trying to bring up the background ambient, keep that shorter IMO - like 1/200th - so you don't get motion blur.

the only reason a modifier would hose the e-ttl (other than maybe a stop of light or so) is that the communication flash from the camera is not getting to it. Are you sure that wasn't the flash you were seeing?


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gonzogolf
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Jul 15, 2011 15:44 |  #13

You may be seeing the preflash, and not the flash itself.




  
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tkbslc
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Jul 15, 2011 15:44 |  #14

I'd bet it was a flash metering issue with ETTL if you are positive the flash is firing. Set the flash to 1/1 manual power and that should tell you.


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Frugal
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Jul 15, 2011 16:09 as a reply to  @ tkbslc's post |  #15

As an aside, what did you have the zoom set to. Doing some experiments pointing my camera toward my Westcott 1 stop shoot through umbrella I found that it worked best with the speedlight at its wide end - 35mm IIR. Zooming the flash to its maximum produced a slightly hotter spot, but only a small part of the umbrella was lit. Now I always use manual zoom with an umbrella.

Oh and manual power too


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How many stops should a shoot through umbrella use up?
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