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<blockquote data-quote="WayneF" data-source="post: 236846" data-attributes="member: 12496">Nikon film TTL did exactly that, metered the flash reflection directly from the film surface, in real time of the final exposure.&nbsp; Worked really well too as to overall&nbsp; exposure, but it could not meter individual flashes.&nbsp; It was real time, and when the light was sufficient, it cut off all the flashes, regardless of their contribution.But digital anti-alias filters put an end to that - reflection no longer worked for digital.So early D-TTL (early digital) painted a light gray strip on the front of the shutter curtain, and metered a preflash reflected from that (after the mirror was raised). There was lots wrong with that system.So Nikon brought out iTTL (about ten years ago),&nbsp; which meters preflfash in the viewfinder (not in the image sensor), similar to the ambient meter, and it doesn't really work quite as well, but well enough, and it does add significant features, like metering the individual flashes for their proper contribution.</blockquote>

[QUOTE="WayneF, post: 236846, member: 12496"] Nikon film TTL did exactly that, metered the flash reflection directly from the film surface, in real time of the final exposure. Worked really well too as to overall exposure, but it could not meter individual flashes. It was real time, and when the light was sufficient, it cut off all the flashes, regardless of their contribution. But digital anti-alias filters put an end to that - reflection no longer worked for digital. So early D-TTL (early digital) painted a light gray strip on the front of the shutter curtain, and metered a preflash reflected from that (after the mirror was raised). There was lots wrong with that system. So Nikon brought out iTTL (about ten years ago), which meters preflfash in the viewfinder (not in the image sensor), similar to the ambient meter, and it doesn't really work quite as well, but well enough, and it does add significant features, like metering the individual flashes for their proper contribution. [/QUOTE]

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