From Moose Paterson...

Nikon first introduced TTL (Through The Lens) flash technology in 1980. The
basics of TTL operation is rather simple and applies to all camera systems.
With TTL flash exposure, when the shutter is tripped, the light from the
flash fires off, racing to hit the subject. This light hits the subject then
bounces back to the camera. The light traveling the speed of light, travels
through the lens (and any filters which may be attached) and strikes the
film plane. The light then bounces down off the film to a sensor which reads
the light as it builds up exposure on the film. Once the sensor and the
connected computer software determines the light has massed enough for the
correct exposure, the camera's computer turns off the flash (just like a
light switch in a house goes on-off). Keep in mind, this is all happening at
the speed of light! Why is this technology so important to flash photography
today?

So in TTL, only the camera needs to know the ISO. The slaves are just that,
they start and stop when commanded by the camera.




On Sun, Jan 11, 2009 at 2:00 AM, Ashok Kumar Kandimalla <
Ashok.Kandimalla@...> wrote:

> Hello all,
>
> I have a D90 and an SB600.
>
> Yesterday I had gone to a photo exhibition where one Nikon rep was
> demonstrating the CLS system with two SB900s (wirelessly) and a D90 (with
> its internal flash being used as the commander). This rep was saying if ISO
> is changed on the camera, then the new ISO has to be set on the remote
> flashes manually. Or in other words there is no automatic communication to
> the slave flashes the ISO info from cameras, though the communication
> between camera and slaves flashes takes care of all the rest like flash
> comp, mode (manual or TTL, etc.).
>
> After I came home I checked the SB600 manual and could not find a method to
> set the ISO at all (in any mode) on the SB600. So it is not clear to me how
> the ISO needs to be set on the SB600.
>
> Regardless of the specific case of SB600, my question is does the ISO get
> automatically communicated to the slave flashes from the camera when using
> wirelessly or not?
>
> Thanks for any help.
>
> Regards
>
> Ashok
>
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