PocketWizard 801-130 Plus III Transceiver is not TTL-capable?!

Started Nov 13, 2012 | Discussions thread
Hugowolf
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Re: PocketWizard 801-130 Plus III Transceiver is not TTL-capable?!
In reply to valmirovimages, Nov 19, 2012

You can’t get TTL flash metering without the preflash on a modern dSLR. On a film SLR it was possible to use the light reflected from the film during the exposure.

Many older film era flash units, like the Vivitar 283 for example, had an auto thyristor mode. The reflected flash light was picked up by a sensor on the flash unit (external metering), and then the light cut when it had reached the requisite level for a ‘correct’ exposure.

IGBT (insulated-gate bipolar transistor) circuits, the modern equivalent of the thyristor, are used for similar purposes. But neither are through the lens (TTL), it has to be via an external light sensor, either on the flash or connected to the flash.

The Canon 580ex II, for example, has an auto thyristor mode (Canon calls it ‘auto external metering’). It is generally seen as a legacy mode.

What are your objections to the preflash metering. The gap between the metering preflash and the real flash are normally less than a millisecond. You can’t see the preflash unless you are using second curtain sync, which delays the real flash until just before the shutter closes rather than just after it opens.

The only problem with preflash is when using slow sync and rear curtain at the same time. This can cause punters to think the image has been captured on the preflash and start to turn away or close their eyes.

Brian A

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