Interesting idea . . .
The flash tubes in the "T" series give off the same brightness, it is the
duration that changes. The two extra contacts on the hot shoe are for
"flash ready" and for "flash quench." When the TTL/OTF sensors in the body
see enough light, they use the "flash quench" line to shut down the flash
(in TTL Auto mode). Thus for slow film and near zero light, the TTL/OTF
will allow a longer flash duration than for fast film under marginal
lighting. In other words, the "T" series work using the same brightness
and changing only the duration to control the quantity of light output by
the flash.
To get the ratios typically used for fill, you would have to activate the
"flash quench" _before_ the TTL/OTF camera circuits would do so (to reduce
the light output from what the camera would normally want). Furthermore,
you would have to do this reliably on a ratio of how long the TTL/OTF would
allow the flash to run.
Unless someone has an electronic trick up their sleeve I'm unaware of, I
don't think this is feasible for TTL/OTF. It would be far easier to
_delay_ the quench than to anticipate when it would happen and do it
beforehand. What might be feasible is a separate sensor to activate the
quench line and running the equivalent of Normal Auto mode (with the flash
in TTL Auto so it will use the quench contact). This would take more
design effort than I care to think about.
At 02:35 6/8/00 , Mike Butler wrote:
>Hey out there,
> While scanning the rec.35mm.whatever newsgroup somebody alluded to a
>TTL Fooling circuit. This would be a means of changing the flash ratio
>but still use the TTL function. Has anyone (Tim maybe) ever heard of or
>have an idea what it would take to make one for the Olympus TTL? My
>thought was to insert it into a T-cord. What do you think?
>
>Mike Butler
>Dublin, California
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