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Canon 580EX: Why can't the flash be disabled? (as in totally!)

Petter Stahre

New member
I wan't to only use the AF-assist function from the 580EX, but without the flash firing ...

... so I set the 580EX as a master and turn the flash off (using the 580EX menue, pressing the zoom button a couple of times and then the wheel (not powering down the flash unit itself of course)). But when shoot with my 1DsII in the Av-mode, I can see that I get different shutter speeds depending on if the flash unit is on or off. From what I understand this shouldn't happen when I've disabled the flash, or?

I know that the 580EX always tries to transmit data to a second flash, using a pre flash, when it's in the master mode (which it needs to be for me to disable the flash).

Apparently this pre flash affects the lightning in the image - which it shouldnt, or? This is evident both by the different shutter speeds (depending on the flash unit being on or off) and I can also see shadows created by the flash firing.

What am I doing wrong? Or can it really be the case that you can't totally turn the flash off - meaning that for "normal" dark scenes the preflash will (almost) not be seen but for very dark scenes the preflash will affect the lightning quite much?

Anyone?

(I also have the ST-E2 but I would like to use the 580EX instead.)

// Petter
 

Ben Rubinstein

pro member
It is known that even with the main flash disabled with wireless ETTL the main tube does output some light while the shutter is open. The solution is to read your cameras manual to find out which of the CF does exactly what you want. On my 5D it is CF-7.
 

Petter Stahre

New member
Ben Rubinstein said:
It is known that even with the main flash disabled with wireless ETTL the main tube does output some light while the shutter is open. The solution is to read your cameras manual to find out which of the CF does exactly what you want. On my 5D it is CF-7.

Thank you for your reply. The problem is that the 1 series doesn't have that function (!).

I've done some searching on other forums and it now seems that this is the situation:

5D+580EX: You can use the AF assist light and totally disable the flash (using Cf.7)
1DsII+580EX: You can't.
1DsII+ST-E2: You can use the AF assist, but the combination acts like there is an extra flash unit somewhere, meaning the shutter speed increases with approx 1 f-stop. (So you have to dial +2/3 or +1 in exposure compensation to get a normal exposure.)

I really can't understand why Canon has produced this handicap for the 1 series!? Why can't the 1 series also have the disable flash function that the 5D has? (And why doesn't the ST-E2 recognize there is no additional flash, meaning the shutter speed should stay the same as when not using flash.)

Anyone from Canon monitoring this who can tell me why this is the situation?

// Petter
 

Will Thompson

Well-known member
Hi Petter, sorry to say there is no way to turn off the pre-flash on the 550-580EX Canon flash units.

You can swivel the flash head away from the subject or cover it up.


The funny thing is that on the 1DsII/1DII the focus assist on the flash just slows down the AF system.

This is why I have the focus assist turned off on My 1DsII & 1DII.


The STE-2 still has a pre-flash, it is just filtered through a nearly IR or IR filter.
 

Petter Stahre

New member
Don Lashier said:
Are you sure that some of this isn't auto-fill reduction? Have you tried turning it off?
- DL

Thanks, I tried disabling it using Cf.14 (1DsII) but with no change. (Ref: http://photonotes.org/articles/eos-flash/index3.html#fec )

(For a minute I was very happy - the AF assist light worked and the flash DIDN'T fire! Wow!! I almost thought this was it until I realized the batteries of my 580EX needed charging. They had just enough power to enable the AF assist light, but not the flash firing. (Maybe this is actually a hidden not-so-talked-about Canon feature? :) ) So after replacing the batteries the same old problem occurs - the flash fires.)
 

Eric Hiss

Member
I think there is a CF to disable the flash but there is another way

Hi,
I am pretty sure that there is a combination of custom functions to disable the flash from firing - but my memory of the 1Ds is fading. You could also use the ST-2 module and I think there is a magic combination for this too and if not at least it will work with some exposure compenstion as was previously pointed out. No doubt if Chuck Westfall happens across this post he will chime in with the answer. The canon flash units really have a lot of features...but they have always been confusing to me.
Eric
 
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