# Pre Flash on a Cano 580 EX?



## willieonline (Mar 21, 2012)

Hello,
I recently attended a wedding and I was taking some photos of some folks dancing in low light.
I was using my Canon 7D with a Canon 580EX. The light was so low, it made it hard for my camera to auto focus.
A few months later, I attended another wedding and I noticed the hired professional photographer had the same lighting 
condition as I did BUT I noticed his flash was firing several times before he took his shot. Almost like a pre flash for the
camera to focus.
Does anyone know if the 580 EX is capable of this, and how it was accomplished?

And is this called Pre Flash?

Thanks for reading.


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## fokker (Mar 21, 2012)

The 580EX should throw out a pattern of red light from the red lens on the front that is designed to help the camera auto focus. I might be wrong but as far as I'm aware the canon speedlights won't preflash for focusing like the onboard flashes do. Are you sure he wasn't just takign a bunch of shots? The flash will prefire in order to meter the flash off the subject, but usually this happens so fast you can't see it.


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## Tiberius47 (Mar 21, 2012)

IIRC, there is a custom function that you can set on the 580 to allow it to either fire the main flash head to focus or just use the red pattern.


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## fokker (Mar 22, 2012)

In what situation would you use the main flash head? More range?


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## ClickAddict (Mar 22, 2012)

Are you sure he wasn't using stroboscopic flash?:   With stroboscopic flash, a rapid series of flashes is fired. It can be usedto capture multiple images of a moving subject in a single photograph.You can set the firing frequency (number of flashes per sec. expressed​as Hz), the number of flashes, and the flash output.


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## ClickAddict (Mar 22, 2012)

The 580 EX II has this capability.  Not sure if the older EX does.


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## Tiberius47 (Mar 22, 2012)

I think the 580 and the 550 have the stroboscopic flash feature.  However, I doubt that it was being used.  It's generally more of a greatly controlled, camera-on-tripod, black-background, shooting action kind of thing.  I doubt it would have been used at a wedding.

You'd use the main flash head for focus if you weren't able to get it with the red pattern.


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## KmH (Mar 22, 2012)

Sounds like the OP needs to re-visit the 580 EX user's manual.


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## Tony S (Mar 22, 2012)

Sounds like what you were seeing is the pre-flash that reads the exposure before the shot was taken.  If he were holding a half press several times without actually taking the shot you could easily see this, where if you are behind the camera you may not notice it at all.


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## Josh66 (Mar 22, 2012)

Tony S said:


> Sounds like what you were seeing is the pre-flash that reads the exposure before the shot was taken.


I agree - the guy was probably shooting with the flash in TTL and it was trying to come up with the right exposure.

The 580EX II does have an AF assist (C.Fn 08), but it uses the red light on the front of it, not the flash head.

He could have also been using the modeling flash (C.Fn 02).

edit
Is your's the "II" or not?  In this case I'm pretty sure they are both the same.


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## Tiberius47 (Mar 22, 2012)

Fraid not.  The flash won't fire the metering preflash until the shutter button is FULLY depressed.  If the photographer was only half pressing the shutter, it wouldn't have been flashing.


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## Josh66 (Mar 22, 2012)

Tiberius47 said:


> Fraid not.  The flash won't fire the metering preflash until the shutter button is FULLY depressed.  If the photographer was only half pressing the shutter, it wouldn't have been flashing.


How do we know he _wasn't_ fully depressing the button?

In low light, at a wedding, can you tell whether someone is fully depressing or half depressing the shutter button from across the room?


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## Big Mike (Mar 23, 2012)

Tiberius47 said:


> Fraid not.  The flash won't fire the metering preflash until the shutter button is FULLY depressed.  If the photographer was only half pressing the shutter, it wouldn't have been flashing.


Unless you put the button for FEL (flash exposure lock). :er:

Also, the photographer in question may have been shooting with the flash set to 2nd/rear curtain sync, so in that case, the preflash would fire, and then there would be a delay before the flash fired again.  This is usually the only time that other people are aware that there was even a preflash at all.  

The flash does have a 'modeling light' feature which is activated (IIRC) by pressing the DOF preview button.  I know that the built-in flash on my 20D, did something similar for AF assist.

But yes, the 580 does have a pretty good AF assist light in the form of a red pattern (to match the AF points).  The key to using this (besides making sure that it is enabled) is that you have to have the camera set to 'one shot' AF mode.  If you have the AF set to AI Servo, the assist light won't function.


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## Tiberius47 (Mar 24, 2012)

O|||||||O said:


> Tiberius47 said:
> 
> 
> > Fraid not.  The flash won't fire the metering preflash until the shutter button is FULLY depressed.  If the photographer was only half pressing the shutter, it wouldn't have been flashing.
> ...


 
I was responding to Tony, who suggested that the multiple flashes might be caused by the photog half pressing the shutter button.


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## Josh66 (Mar 24, 2012)

Big Mike said:


> The flash does have a 'modeling light' feature which is activated (IIRC) by pressing the DOF preview button.


There are a few (4) different options on that custom function...  You can assign it to the DOF preview button, the test button on the flash, DOF preview and test buttons at the same time (that one would be tricky without a third hand), or off.  That's on the 580EX II - not sure if the 'non-II' has all of those options.


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