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Archive 2011 · Pretty basic flash question/problem
  
 
David Kirsch
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p.1 #1 · Pretty basic flash question/problem


I'm having some difficulty with using flash indoors. I'm using a 7D and Canon 580EXII mounted on the camera. Shooting manual I'm WAAAY underexposed. Just for giggles I tried a shot on the green square and it was pretty spot on. ISO 400, f 4.0, 1/60. So, using those settings I switched back to M and dialed in 1/60 at f4.0, ISO 400. Should be the same exposure, right? But it's not! It WAAAAY underexposed. Why is this. How can I get a good flash exposure using manual settings?

Thanks for the help

David





Green square exposure

  Canon EOS 7D    EF-S17-55mm f/2.8 IS USM lens    55mm    f/4.0    1/60s    400 ISO    0.0 EV  







This is manual with same exposure settings

  Canon EOS 7D    EF-S17-55mm f/2.8 IS USM lens    55mm    f/4.0    1/60s    400 ISO    0.0 EV  




Dec 06, 2011 at 03:56 AM
alohadave
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p.1 #2 · Pretty basic flash question/problem


The flash didn't go off in the second shot.


Dec 06, 2011 at 04:09 AM
David Kirsch
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p.1 #3 · Pretty basic flash question/problem


Good try, Dave, but I've checked the metadata and flash did fire. You can also check if you have Opanda or some other EXIF reader -- "flash fired, compuslory flash mode." Plus, I remember seeing the flash, too. So that's not it.

David



Dec 06, 2011 at 04:50 AM
ragebot
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p.1 #4 · Pretty basic flash question/problem


Might be a recycle time problem.


Dec 06, 2011 at 06:14 AM
BrianO
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p.1 #5 · Pretty basic flash question/problem


David Kirsch wrote:
I'm having some difficulty with using flash indoors. I'm using a 7D and Canon 580EXII mounted on the camera. Shooting manual I'm WAAAY underexposed. Just for giggles I tried a shot on the green square and it was pretty spot on. ISO 400, f 4.0, 1/60. So, using those settings I switched back to M and dialed in 1/60 at f4.0, ISO 400. Should be the same exposure, right? But it's not! It WAAAAY underexposed. Why is this.


You were in Manual exposure mode, but what was the flash mode set to?

In "Green Square" mode, the camera takes care of everything with no user input. It will force the flash into ETTL Autoflash mode and set the power level it deems correct.

When you switched to Manual mode, if the flash was set to Manual Power and a low setting dialed in, or if there was negative flash exposure compensation (FEC) dialed in for ETTL Autoflash, the image could be underexposed.

One of the things to watch for with the 7D (and some others) and the 580EX II is that some flash settings can be set on both the flash and the camera menu, and if different they can conflict with each other. It takes a good read of the manual to know which ones have priority over-ride authority.



Dec 06, 2011 at 08:51 AM
cgardner
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p.1 #6 · Pretty basic flash question/problem


Agree that something operator related caused the problem in the second shot but it is difficult to tell what.

Something to be aware of when composing flash shots is distance to your main subject vs. other objects in the frame. ETTL-II makes two zone maps of the scene for comparison: one ambient the other with pre-flash. That mapping process allows the camera metering to determine what is reflecting the most light from the flash back to the camera. In your shot it's the white edge of the counter on the right which is closest to the camera.







That area has an eye dropper reading of 242 - 249, which is where a solid white object should be. The metering seeing this was the brightest object based the overall exposure on it. But the same counter material next to the girl a more similar distance to her face is at 156-161 which is underexposed considerably. The white pan even further back is rendered 148-159.

If you simply raised FEC until the girl is correctly exposed the counter on the right will become a blown out distraction. While that is a solution, it's not the best on. The best way to tell the metering "This is most important - expose it correctly" is to compose your flash shots so what is most important is closest to the camera and flash.

The "red eye" in the shot is a result of the low angle of the flash. Using a flash bracket and OC-E3 cord will eliminate that problem and also make the modeling in your single flash shots much more flattering, like this one...









Dec 06, 2011 at 12:03 PM
Chris Beaumont
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p.1 #7 · Pretty basic flash question/problem


If you look at the hot spots (pepper grinder, taps, cupboard knobs) they all appear to be in the same place in both shots.

Would imply to me that flash DID fire....but probably at 1/128 on manual mode.

Either press mode until it displays E-TTL or press the button in the middle of the scroll wheel and scroll to a higher power



Dec 06, 2011 at 12:14 PM
David Kirsch
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p.1 #8 · Pretty basic flash question/problem


ragebot wrote:
Might be a recycle time problem.



Nope, I had fully charged batteries and I waited between shots. You'll notice that the shots are not consecutively numbered, but I know I waited more than enough time between all shots for recycle. I'm pretty confident that's not the issue.

David



Dec 06, 2011 at 05:34 PM
David Kirsch
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p.1 #9 · Pretty basic flash question/problem


BrianO wrote:
You were in Manual exposure mode, but what was the flash mode set to?

In "Green Square" mode, the camera takes care of everything with no user input. It will force the flash into ETTL Autoflash mode and set the power level it deems correct.

When you switched to Manual mode, if the flash was set to Manual Power and a low setting dialed in, or if there was negative flash exposure compensation (FEC) dialed in for ETTL Autoflash, the image could be underexposed.

One of the things to watch for with the 7D (and some others) and the 580EX II is that
...Show more

Brian, that's a good thought. But flash was set to ETTL-II and FEC was 0. You may have hit the spot with the camera overrides. I hadn't thought of that, but I'll give it a look. What surprises me is that the nominal exposure (f-stop, shutter speed and ISO) are the same, so obviously something's going on with the flash to cause it to reduce power in manual mode.

David



Dec 06, 2011 at 05:37 PM
 

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David Kirsch
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p.1 #10 · Pretty basic flash question/problem


Chris Beaumont wrote:
If you look at the hot spots (pepper grinder, taps, cupboard knobs) they all appear to be in the same place in both shots.

Would imply to me that flash DID fire....but probably at 1/128 on manual mode.

Either press mode until it displays E-TTL or press the button in the middle of the scroll wheel and scroll to a higher power



Chris, as I said above, the flash was in ETTL-II. Also as above, I need to check to see if some camera setting is overriding the on-flash setting.

David



Dec 06, 2011 at 05:41 PM
cgardner
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p.1 #11 · Pretty basic flash question/problem


Check to make sure you didn't set the flash to Master mode. The interface is somewhat confusing in that regard since OFF means turn the wireless slave control off, not the flash itself.

(Wireless) OFF = Single Flash use

MASTER = Use when the flash in hot shoe / OC-E3 cord is acting as Fill and controlling a Slave flash

SLAVE = Used when the flash is used off camera triggered by 580ex/580exII, ST-E2 controller, or 7D built in flash in Master mode.



Dec 06, 2011 at 05:44 PM
David Kirsch
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p.1 #12 · Pretty basic flash question/problem


cgardner wrote:
Agree that something operator related caused the problem in the second shot but it is difficult to tell what.

Something to be aware of when composing flash shots is distance to your main subject vs. other objects in the frame. ETTL-II makes two zone maps of the scene for comparison: one ambient the other with pre-flash. That mapping process allows the camera metering to determine what is reflecting the most light from the flash back to the camera. In your shot it's the white edge of the counter on the right which is closest to the camera.

That area has an
...Show more

Thanks Chuck. That is some awesome info! How the heck did you do those eyedropper measurements and arrows? Very cool and VERY helpful to understanding your response.

First, I agree it's an operator problem!

Second, I usually shoot flash with an off-camera bracket (RRS B-87B) and OC-E3 cord, but I was lazy this time. I don't think that would change the basic exposure problem I'm having, though (but it would, as you say, likely cure the red-eye problem)

Third, and most important, what's confounding me is that with the same exposure settings (f-stop, shutter speed and ISO) and not changing any setting on the flash, why would 2 exposures, one green square - one manual - be so different? For what is basically the same scene, why is green square pretty good but manual so underexposed? [As discussed in some previous posts, I do need to check and see if I have set something on the camera that's overriding the flash setting]. I don't want to shoot green square. I am aware of its limitations and want to have the control manual allows. Does the flash/camera meter differently in ETTL-II mode in green square than in manual in determining the amount of flash? I guess I could put the flash in manual mode, too, and adjust power until exposure was right, but do I have to give up ETTL? Manual flash may be optimum, but with my granddaughter running around the house I'd often be guessing about flash power (at least until I have a lot more experience with flash!)

Thoughts?

David





Dec 06, 2011 at 06:00 PM
David Kirsch
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p.1 #13 · Pretty basic flash question/problem


cgardner wrote:
Check to make sure you didn't set the flash to Master mode. The interface is somewhat confusing in that regard since OFF means turn the wireless slave control off, not the flash itself.

(Wireless) OFF = Single Flash use

MASTER = Use when the flash in hot shoe / OC-E3 cord is acting as Fill and controlling a Slave flash

SLAVE = Used when the flash is used off camera triggered by 580ex/580exII, ST-E2 controller, or 7D built in flash in Master mode.



Chuck, that's a great thought! I have messed with that setting because I do have a second flash and was playing with it once. Maybe I didn't reset it. Now I just have to get through this workday and go home tonite and see if that's it.

David



Dec 06, 2011 at 06:03 PM
David Kirsch
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p.1 #14 · Pretty basic flash question/problem


UPDATE:
I have come to the conclusion that the most likely cause of the underexposures may have been bad ETTL contact. I remounted the flash on the body and checked the camera's flash menu. Nothing was set that would affect this. I also verified that the flash was not set to Master or Slave - just basic setting, and to ETTL. I tried a few more exposures, first on green square so I could match the exposure values, then on manual using the same values. Voila! almost exactly the same exposure! I also tried it on a 5DII and got the same results - basically identical exposures on green square and manual with the green square settings.

I guess the lesson here is to make sure to mount the flash will, so all the contacts make good contact. I imagine the same will hold true when I use the off camera cord - make sure all the mountings are solid. I will always take a test shot from now on to make sure I'm ok.

Thanks for your inputs.

David



Dec 09, 2011 at 06:22 PM
Greggbhill
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p.1 #15 · Pretty basic flash question/problem


Not sure if it helps, but there is a thread in the canon forum about the 580ex and issues relating to the connection pins... http://www.fredmiranda.com/forum/topic/1067162


Dec 09, 2011 at 11:10 PM
David Kirsch
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p.1 #16 · Pretty basic flash question/problem


Thanks Gregg. I think the guy who said to wiggle it on mounting and then push again has it spot on.

David



Dec 09, 2011 at 11:27 PM
BrianO
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p.1 #17 · Pretty basic flash question/problem


David Kirsch wrote:
...I think the guy who said to wiggle it on mounting and then push again has it spot on.


I get lucky sometimes.



Dec 10, 2011 at 05:01 AM





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