I'm sure it uses distance info some how but at the
same time it doesn't warn you when you choose certain
apertures like F16 pointed at something 50 ft away. 

--- tom <[EMAIL PROTECTED]> wrote:
> On 13 Mar 2002 at 14:54, Peifer, William [OCDUS]
> wrote:
> > 
> > I guess the way to test Tom V's idea (about the
> possibility that the flash
> > intensity is calculated from distance and guide
> number information, but not
> > controlled by an actual TTL sensor reading) 
> 
> I backed away from that...;)
> 
> I'm wondering if distance info is used at all in TTL
> flash discharge, and if so, how.
> 
> > is to fire a test shot with and
> > without the lens cap in place.  If the TTL sensor
> doesn't matter, then the flash
> > intensities for both of these test shots should be
> about the same, and the
> > recycle times should be about the same.  If the
> sensor really ~is~ metering and
> > controlling flash output, then the
> lens-cap-in-place test shot should have a
> > ~much~ longer recycle time.
> 
> The test I have in mind involves testing A vs. FA
> lenses (I'm assuming A lenses have no distance
> info).
> 
> tv
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