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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 28 Feb 2005 (Monday) 15:47
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Please help 580ex 420ex settings ????

 
J.A.F. ­ Doorhof
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Feb 28, 2005 15:47 |  #1

Boy do I feel stupid but I'm really stuck.

I just bought the 580EX and I allready have a 420EX.
Today I tried somethings but I'm really stupid or I'm missing something :D.

I have the 420EX on a white background and the 580ex on my 20D.
Setting ETTL
When I set the ratio to max left 1:8 I believe I have an almost blownout background and proper light on my subject.
When setting it to max right I believe 8:1 I have way to low light from both flashes.

What I wanted to do was the 420EX on full power and the 580EX on lower power so I tried the following.

Set the manual A on 1/1 and B on 1/128 both performed way to low.
Set the manual A on 1/128 and B on 1/1 both blew out the picture.

To get it almost the way I wanted I set FEC to +2 2/3 and ratio to the far left this gave good skin and an almost blowout back.

I must be missing something and the manual is VERY VERY poor in explaining ratio's, it tells it about 2 groups and 3 groups but even then the ratio's are not well explained.

Can someone please tell me what I'm doing wrong ?
I can work my studio setup but it would be nice if I also mastered this.

And again I'm probarbly missing something and I feel really stupid but I'm stuck so please help ??

Greetings,
Frank


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robertwgross
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Feb 28, 2005 15:58 |  #2

Have you read Scott's sticky about ratios?

---Bob Gross---




  
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J.A.F. ­ Doorhof
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Feb 28, 2005 16:05 |  #3

Will do right away.
One other thing by the way.
When set to master it seems the 580EX has alot less power.
The 420EX was aimed at the white background I turned arround and made a shot of the room and I could not get the whole room lighted, when switching to off, the whole room was bright.

But I will first read Scott's stuff.


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J.A.F. ­ Doorhof
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Feb 28, 2005 16:19 |  #4

Ok let me see if I understand, please correct me if I'm wrong.

The problem here is that I use ONE master 580EX and one slave 420EX.
The 420EX measures the white background and will lower the output for flashoutput resulting in a problematic scene.
BUT will it also lower the output of the 580EX ?

The problem I had.
The model was sitting in front of the white.
I used everything on ETTL.
The white background was not blown out and the model was WAY too dark.
When changing the ratio to the far left, the model got some better and the white of the backdrop almost blew out. When combining this with a fec of 2 2/3rds it was as I wanted.
But I have no clue what I did ?? :D.

Question 1:
When the 420EX measures the white background it will light this just below blowout because the systems doesn't want to blow out whites (perfect can be solved by raising the fec 1 stop).
BUT will it also affect the output of the 580EX.
My understanding was/is that the 420EX will measure the background and adjust and the 580EX will measure the model and adjust.

Question 2.
Can it be that I have set the 420EX wrong ? I use channel 1 group A.

Question 3:
Is my master 580EX a group A or group B or no group at all.
When I set the Manual flash output to 1/1 I blow out everything, when I set group A or B to 1/128 I get no lighting to talk about (very low).

Question 4:
What is controlled by the fec ?
Only the 580EX or both flashed.
Also I have the idea that my onboard (20D) flash exposure doesn't do anything anymore, with the 420EX it can give more power to the flash but with the 580EX it seems not to work anymore (no big problem there I can set it on the flash).

I now understand the ratio's.
When getting two groups, lets say group A a 420EX and group B a 420EX and I want group B to give more light I change the ratio to the left or right evening the balance between the groups, far right group B more light A less and visaversa.

I understand E-TTL.
A preflash is given on which is measured the output and this is calculted in the flash.

My understanding WOULD be in this case.
Model in front of the white backdrop, face is perfect lighted with the 580EX and the background is just under blowout with the 420EX.
What happens is the background is just under blowout but the model is way too dark.

Sorry for the long posts.


Greetings,
Frank


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PacAce
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Feb 28, 2005 16:29 |  #5

Have you tried setting the ratio to (A:B):C? Since the 420EX is going to be used as aux lighting and not for subject lighting, it should be set to C. This can then be controlled independently using FEC for C. Since you won't really have a B group, you can set the A:B ratio to 1:1.


...Leo

  
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scottbergerphoto
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Feb 28, 2005 17:05 as a reply to  @ PacAce's post |  #6

Frank,
In wireless ETTL with ratios, the Master on the camera (580EX) defaults to group A. Your 420EX, must be set to group B. If you add a group C flash, keep in mind that the ratios are (A:B) : C, not A:B:C.

If you prefer to control the output directly on each flash, put both flashes in Group A, and dial in FEC as you like on each flash. If you leave them on different groups as you would for wireless ETTL, the FEC on the Master will contol the Slave as well.

Regards,
Scott


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Jim ­ Larson
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Feb 28, 2005 20:34 |  #7

I am confused. First: Is this ETTL (10D or 300D) or ETTL-II (20D)? They will produce radically different results in the setup you describe.

You want the 420EX set to group "B". The 580 in the shoe set to group "A".

Set ratio to suit on the 580EX. I know that if my 550EX is set to "manual", the 420EX will not fire. End of story. The 420EX wil fire in ETTL only. End of story. It does not have manual controls.

FEC set on the master unit will affect ALL flash units. FEC on a slave unit will affect the slave only (you don't have this option: The 420EX does not have a FEC control)

Flash exposure is controlled by the camera. Not the flash. Camera calculates ratios based what it sees in the preflash. The *body* will figure out the flash power for both units based on the ratio dialed in on the 580 based upon how each flash (firing its own preflash) exposes the scene.

Yes, there are actually *five* bursts of light when you have an A:B Ratio. They are Command pulse, Preflash A, Preflash B, (camera does math) Command pulse, FLASH FOR EXPOSURE.

If this is a 10D (ETTL flash), then if the SLAVE can't properly expose the subject, you will see a blinking flash icon in the viewfinder (alerting you to a problem), and the flash will fire at FULL POWER. Note that in ETTL, the body exposes the FOCUS POINT ONLY. If the focus point is a face, and you are firing the 420EX at the BACKGROUND, the 420EX won't be able to expose the subject at all and will fire at full power.

If the 420EX is fired so that it CAN expose the subject, then the ratio calcs will be performed and life will be good.

If you have an ETTL-II camera. . .I don't know what happens. I suppose the 420EX will fire and the zones will be computed as normal. It sounds like you have an ETTL camera.

Want to expose background with an ETTL camera? You need a 550EX or 580EX flash. Why? Because if the flash isn't exposing the focus point. . .ETTL flat out won't work and the flash must be fired in manual. End of story.

Hope this helps.




  
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Jim ­ Larson
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Feb 28, 2005 20:50 |  #8

Ah. Reread the post. You have a 20D.

FIRST: Remember, flash exposure is done by the body. There are no exposure sensors in the flash units. The flash units only respond to the commands from the body.

SECOND: Your camera has ETTL-II. It measures -and averages- light in 17 zones(?) to compute flash exposure. It actually does not know - nor care - where the subject is located. If your flashes are setup so that one flash exposes ONLY 7 zones and the other flash exposes 10 well and the other 7 weakly. . . I would have NO CLUE WHATSOVER what the result will be!

But underexposing the subject makes sense. . .It may actually think the area of interest is the background and be throwing out the zones with subject in it. . .

For a studio setup like this. . .you almost would wish for conventional ETTL no?

Third: You may want to try ETTL-II "Averaging" rather than "Evaluative", via CF14. "Averaging" throws out some of the more funky ETTL-II corrections, and may give you better results. It does not, however, change the averaged 17(?) zone metering.

Forth: I have no clue how you get good results in this setup with ETTL-II. With a primary subject lit by one flash and background with a different flash. . .I would be inclined to say you need to fire BOTH flashes in MANUAL. .. which unfortunately won't work with a 420EX as the slave flash.

If you had ETTL (ie, a 10D) you could fire the Master flash in ETTL, but the background flash would still need to fire in MANUAL.

I have a 10D, 550EX, 420EX and ST-E2. I don't have problems, but I always make sure both flashes can expose the focus point.




  
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J.A.F. ­ Doorhof
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Mar 01, 2005 00:00 |  #9

Hi,
I have a good studio setup, this is only used for some location work.
I will try putting the 420EX in group B and than checking will do so after work today.

One more question (thanks for all the answers by the way it's really appriciated).
You mentioned that FEC on the body only works.
How is it possible that when in Master slave mode this does nothing while raising the fec on the 580EX will do the trick ?

I have high hopes that with the group B setting it will work, I will post the result tonight.
Never thought of that (shame on me)

Greetings,
Frank


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scottbergerphoto
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Mar 01, 2005 06:25 as a reply to  @ J.A.F. Doorhof's post |  #10

There are some errors in the above posts, I believe due to a misunderstanding of how ETTL and ETTLII work. You absolutely can use the 420EX to light the background and it will not fire at full power. It will be controlled by the ratio you set on the Master. In addition In ETTLII, when CFN. 14 is set to "0" (default), that is Evaluative or Subject Based Flash Metering. It is not AF point based. It throws out the extreme values of reflected light. It is supposed to identify the subject by the pattern of reflected light from the 17 metering segments. This eliminates the problem of using flash with focus and recompose. When Cfn. 14 is set to "1" Averageing, all 17 metering segments are averaged together with no attention paid to a specific subject.
There is alot more on this in the EOS Flash Sticky.

These pictures were done in wireless ETTL using a 10D, with two 550EX's and a 420EX. One 550EX was on the camera (A-Master), one 550EX was on a lightstand (B-Slave) and one 420EX was behind the subject for the background (C-Slave).
http://www.pbase.com/s​cottbergerphoto/ayana_​bailey (external link)
Regards,
Scott


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PacAce
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Mar 01, 2005 09:27 |  #11

Not to sound like a radical or anything but I think the 420EX should be set up as a group C flash and it's output controlled independently of the main subject flash if it's going to be used for lighting up the background and not the subject. The A:B grouping ratio is more suitable when both flashes are lighting up the subject and you want to set up a different lighting ratio between the two. Even if you don't have a group B light, the background lighting flash should still be set up as group C. I think, IMHO, the lighting control just works out better that way. Not that you can't use the background light as a group B light but what that means is that the main flash (group A) is going to be ratioed to the background and not the subject since the background is the only "subject" which will get lit by both the main flash and the secondary flash and I don't think that's what you reall want. Just my 2 cents.


...Leo

  
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J.A.F. ­ Doorhof
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Mar 01, 2005 09:42 |  #12

I need all the cents I can get :D
But I believe I understand my mistake I never figured that the 580EX would be a group A when I started (duh :D) now I think I can make the balance much beter.
I will try tonight or tomorrow morning.


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Jim ­ Larson
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Mar 01, 2005 10:26 as a reply to  @ PacAce's post |  #13

PacAce wrote:
Not to sound like a radical or anything but I think the 420EX should be set up as a group C flash and it's output controlled independently of the main subject flash if it's going to be used for lighting up the background and not the subject.

You are completely correct. The only problem is that the 420EX lacks manual controls. It can ONLY operate in ETTL mode.

If you had another 550/580EX, you could set it up the way you suggest(actually, it would work fine in Group B or Group C)




  
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PacAce
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Mar 01, 2005 11:01 as a reply to  @ Jim Larson's post |  #14

Jim Larson wrote:
You are completely correct. The only problem is that the 420EX lacks manual controls. It can ONLY operate in ETTL mode.

If you had another 550/580EX, you could set it up the way you suggest(actually, it would work fine in Group B or Group C)

But you don't need manual control to work the 420EX in group C. The 550ex or the 580ex (as the master) will take care of it very easily.


...Leo

  
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scottbergerphoto
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Mar 01, 2005 11:44 as a reply to  @ PacAce's post |  #15

PacAce wrote:
But you don't need manual control to work the 420EX in group C. The 550ex or the 580ex (as the master) will take care of it very easily.

Exactly! and Leo, your 2 cents is worth at least a nickle around here.
Scott


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Please help 580ex 420ex settings ????
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