Need a "professional" lens e-510

Started Apr 26, 2012 | Discussions thread
Klarno
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Re: Flash questions
In reply to Silvercobra, May 9, 2012

Silvercobra wrote:

I don't quite understand TTL. From reading it seems to be about metering, whether the flash output is determined by the camera reading or the flash reading, but I thought flash power was controlled by the user (full power, 1/2, 1/4 etc). Would the yongnuo be able to have its flash power adjusted?

What you describe is correct for manual flash exposure. But there is also automatic flash exposure, which is what TTL is about.

TTL means "through the lens". Older Automatic flashes have something called a thyristor, which cuts off power to the flash tube when a sensor detects a certain level of illumination. That sensor used to be on the body of the flash, the downside being that that sensor would see a different view from the lens you have on the camera. With a TTL flash, this sensor is in the camera, the same as the camera's own metering sensor, so it can see the exposure through the lens, with the same aperture.

Now automatic exposure uses a pre-flash, which determines the correct power for the flash with a brief, low power strobe before the image is captured. But the principle is the same.

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