# Canon 5D Mk III pre flashing.



## downtime (Jan 19, 2015)

I have a colleague with 5D MkIII.
Recently I witnessed a subject blinking 10 shots in a row all caused by the pre flash.
We tried different flashes including aftermarket and the same result. I soon realized that it was the cause
of blinking on other subjects as well. Obviously the subjects are very sensitive. Regardless, this has to be turned off.
Does anyone out there know how to fix this? Switching from ETTL to TTL does not come up as an option in the camera's
flash control menu. It does not happen with flash in full manual mode but for this shoot it's not a viable option.

Anyone have an idea how to fix this?


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## WillThompson (Jan 19, 2015)

Get a EOS 1V, set to TTL, and shoot film.

Or get a 600ex flash and shoot in auto mode ie sensor on the flash for AE.


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## neuroanatomist (Jan 19, 2015)

Fix what? The system is operating normally. The preflash is required for E-TTL flash metering. If you need to eliminate the preflash, set the flash power manually.


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## Ian_of_glos (Jan 19, 2015)

I would be very surprised if your model has time to blink in between the pre-flash and the actual flash. The two flashes take place in a few milliseconds and for most people it looks like there is only one flash. It is more likely that the model is blinking in response to the AF assist and this can be disabled on the Canon 5D mk3 in the AF3 menu. Let me know if this makes a difference


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## tolusina (Jan 19, 2015)

A daughter's former boyfriend had a fast enough blink reflex that it was impossible to get a flash photo of him with open eyes. He was well aware of the reflex, warned me in advance, he was powerless to overcome the reflex.

I hadn't yet acquired bounce flash techniques so it's unknown if bouncing could have avoided his reflex.

10 in a row, might be your subject, not your gear.


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## Gert Arijs (Jan 19, 2015)

I'm not 100% sure, but I think you could use FEL (flash exposure lock). This would separate the pre-flash with the flash.


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## sanj (Jan 19, 2015)

neuroanatomist said:


> Fix what? The system is operating normally. The preflash is required for E-TTL flash metering. If you need to eliminate the preflash, set the flash power manually.



This.


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## privatebydesign (Jan 19, 2015)

Some great suggestions here, and as Neuro said, pre flash is a necessary function of ETTL.

So, switch to manual, or (as Will so fully said) get a Canon EOS film camera and shoot TTL, or get the 600-EX-RT (or any other flash with a thyristor cutoff) and shoot in thyristor mode.

Another option, and the last I can think of, is to use a long shutter speed and second curtain sync. The average human blink takes 300-400 milliseconds, so use a 1/2 second shutter speed, which isn't an issue if you are shooting in controlled situations as the flash duration is your effective shutter speed, and the blinker will have opened their eyes again by the time the true flash fires.

But truthfully, manual flash is the way to go.


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