In theory the same energy spread between two tubes should give identical total
light output as the
same energy dissipated in only one tube.
However, two things reduce this :
1) the reduced energy dissipated in each flash tube, reduces the peak
temperature of the tube
plasma. The light conversion efficiency is higher with the higher temepratures
in a single tube.
(It is a little more complex, because it depends on what is actually produced
in the visible
spectrum.)
2) the tubes are in series in the T28 (see schematic on Marks Website), so
voltage acrosss each
tube is reduced ~1/2 of single tube.
Since the capacitor does not discharge to zero but to the extinction voltage of
the tube (volt =
~60V) then with two tubes in series there is quite a bit more energy left in
the capacitor (volt=
~120V) after flash completes. (a factor of 2^2 - 1 = 3x more wasted) This is
increased wasted
energy, unsued at end of flash.
Tim Hughes
--- Jeff Keller <jeffreyrkeller@xxxxxxxxx> wrote:
>
> The guide number is limited by the energy stored in the capacitors and
> the width of field illuminated. If two heads are sharing the same
> energy it seems reasonable that the guide no. would go down ...
> -jeff
>
> On 7/19/07, usher99@xxxxxxx <usher99@xxxxxxx> wrote:
> >
> > Piers,
> > Thanks again for these.?
> >
> > Weird that on the Alan Wood site in one place near where he mentions the
> > calculator panels
> (T28), the? GN with one flash is listed as 22 and 28 with 2 heads.? It is the
> opposite later on
> his site and anywhere else, including on your panel pdf.?? Must be a mistake
> on the AW site.? I
> don't know how the GN would go down with 2 heads (must be the case), unless
> the controller T
> power control attenuates the power to both.? Perhaps there is something weird
> about GN's at
> macro distances.? Manual macro flash shouldn't be as weird as quantum
> effects, though Heisenberg
> seems to lurk over my shoulder when I try it.
> >
> > http://www.alanwood.net/photography/olympus/t28-macro-twin-flash.html
> >
> > Mike
>
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