----- Original Message -----
From: "Godfrey DiGiorgi"
Subject: Re: OTS Metering?
On Dec 20, 2005, at 2:07 PM, Tim Sherburne wrote:
Are you sure they're not accomplishing the TTL metering another
way? AFAIK, the LX is the only Pentax body with "off-the-film" metering,
but
there are plenty of Pentax bodies with TTL flash metering capabilities.
Well, they is no pre-flash, and they have read the light coming through
the lens at exposure time. The mirror is up, so you can't read it off the
focusing screen, and you can't read it on the way to the sensor without
whatever you're using to read it being in the way of the sensor.
Therefore, they have to be reading it as reflected off the sensor.
TTL flash metering, by definition, is taking reflected readings off the
film/sensor.
OTOH, TTL flash as done on the istD has been less than accurate for me.
Preflash measurement is more accurate, I am led to believe, but has the
downside of slowing camera responsivness.
Accurate automatic flash has been the best compromise I have found.
Tim is confusing TTL flash measurement with the automatic exposure via
continuous OTF light measurement, which is unique to the LX (at least I
haven't heard of another camera that does it), and only works at speeds
below flash sync, the further from sync speed, the better chance it has of
working.
William Robb
