Guidance on GN flash ouput.

Started Jul 7, 2011 | Discussions thread
gisle
Senior MemberPosts: 2,468
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Re: Guidance on GN flash ouput.
In reply to Desmond Ong, Jul 7, 2011

Desmond Ong wrote:

Thks for the guidance.. I get to understand better in the GN mode. It really takes some physics calculations in it But it seems like its function same as TTL.

TTL-mode works by having the light meter in the camera actually measuring the light reflected by the flash. That's why it works when you're bouncing etc.

GN-mode doesn't measure anything - it just does the purely mechanical GN computation (as already described by WFulton) for you.

Since GN can only be use in direct flash, for e.g if my subject tend to be 10 ft away and my aperture set to f8 therefore GN should be 80. Does TTL able to produce the same amount of intensity at such distance apply?

The maximmum light output is roughly the same in all modes. A tiny bit of power is wasted in TTL-mode for a metering pre-flash, so the GN and M modes will give slightly more range - but I would not worry about it.

The GN of your flash depends on the ISO setting, the position of the zoom head and the illumination pattern selected. It is supposed to be 92 (ft) at ISO 100 with the zoom set to 35 mm, with standard illumination pattern.

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