TTL - What does it mean?

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rereg2010

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Hi all,

Pretty new to all this and still feeling my way round things.
With regards to flash I've seen TTL mentioned a few times, what is it and how does it work?

Thanks
 
Transistor-Transistor Logic, as in digital circuits

Time To Live, as in computer data

Through The Lens, Photographic meaning
:)
 
rereg2010 said:
So how does the commander unit work?
Click to expand...

You only need a Commander unit (Master in Canon speak) for multi-flash remote setups. For regular flash any Nikon CLS/iTTL (Canon E-TTL) compatible gun will do.

When you press the shutter release, the flash immediately fires a low power pre-flash which is reflected back off the subject and measured, and the flash power is set. Then the shutter opens and the flash fires at the correct output. This all happens so quickly that the two flashes appear as one to the naked eye.

With multi-flash set ups, all the other remote guns are instructed to fire a pre-flash and they too are measured. Then the commander sends a series of coded pulses instructing each gun what to do, then the shutter opens and they all fire in sync at the correct output. This also happens so fast it looks like just one flash.

That's the basis of it. Pretty amazing technology TBH.
 
Thanks for that HoppyUK, sorry to be a pain..

SO how does the Master Flash communicate with the other off camera units?

Thanks
 
rereg2010 said:
Thanks for that HoppyUK, sorry to be a pain..

SO how does the Master Flash communicate with the other off camera units?

Thanks
Click to expand...

Paragraph three ;) By high speed morse code like flashes, fired at up to 50,000 per second :eek: It's visible light when it comes from a commander gun (or commander pop-up) or semi-IR when it comes from a commander-only unit like the Nikon SU-800 (Canon ST-E2).

But light anyway, which is why you need direct line of sight between the commander and remote guns, unless they are very close. And they can stuggle in bright daylight for the same reason, because the sun overwhelms the flashes.

There are only a couple of radio triggers that do auto-TTL, Pocket Wizards and Radio Poppers, and they're £400 a set.
 
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