How much light does CNTL flash "spill" into scene?

Started Jan 10, 2013 | Discussions thread
sybersitizen Forum Pro • Posts: 10,871
Re: How much light does CNTL flash "spill" into scene?

cplunk wrote:

  1. How does a wireless remote work with ADI? ADI takes the distance, measured from focusing, and figures out the amount of flash based based on that? With a certain aperture, ISO, a quick calculation should tell you the amount power the flash needs to output based on the distance, using that inverse square law. But, the camera has no idea how close, or far that wireless slave is so how could it ever determine the power required for that?
  2. With TTL, the camera fires the flash, figures out how much power it needs metering through the lens, then opens the shutter and fires at that power. Wirelessly, I'm assuming, the controller must tell the slave to fire, the camera meters that, decides how much the power it needs the slave to actually fire, tells the slave that, shutter opens, command to slave to fire. Does that sound about right? But if there is no slave for the preflash, what's it do? It has nothing to meter from the slave, so what does it do?

The #1 paragraph is incorrect, another common misconception. ADI works exactly the same as TTL (and it still requires a pre-flash) except that distance information is also taken into consideration along with the flash metering decisions. It's supposed to improve the results, but it rarely works out that way. Experienced Alpha system users generally ignore the ADI option and stick with TTL.

The #2 paragraph is pretty much correct. However, there is always a pre-flash in every autoflash scenario - pop-up, shoe-mounted, cabled, or wireless. And wireless autoflash requires more than one pre-flash.

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