The numbers on the chart are too tiny for me to read them easily but I
do note that the time scale is in milliseconds and stretches over many
of them whatever the actual scale. A small portable electronic flash
may have a flash duration as little as a 1/50 of a millisecond or even
shorter. A big studio electronic flash might have a duration as long as
1 millisecond. All much, much too fast for the camera to handle in its
normal auto mode.
In order for TTL FP mode flash to work in auto exposure mode the flash
duration must be at least as long as the flash sync speed. For an OM
body that's at least 1/60 second or 17 milliseconds. If you look at the
ramp up/ramp down curves on those FP graphs you can see that getting
some stable light will take a while which is why the FP sync starts
ignition of the bulb before the shutter opens. Some additional timing
slop would probably also be desirable so I think I'd like to see a burn
time of 35 milliseconds or more. Even so I'm still not sure it will work.
Dr. Flash
On 4/16/2011 4:06 PM, usher99@xxxxxxx wrote:
> JK writes:
>
> --I probably missed something but aren't flash bulbs slower to reach
> peak
> --output than an electronic flash ... different settings on the camera
> x-synch
> --vs fb? I guess I've always just assumed they burned longer too.
>
> Yes,
> See below, the FP bulbs have a nice long plateau when they burn. The
> OM2 has an FP setting that fires the FB ?10msec or so prior to
> first curtain though X synch will work with a slow shutter speed. I
> have a neat dookicky from John that locks it in place
> so I don't have anymore untoward foul ups from the switch becoming
> inadvertently altered.
> I see replacing these monster FB's cost a pretty penny.
> It is promising that Dr. Flash thinks it may work in TTL auto. The GN
> does vary with the reflector and shutter speed and I will fire 2 to
> three but only really
> need to be sure I don't overexpose by much. I will set it up on a
> tripod per the previous diagram from JK. He should look NE Mon PM and
> may perhaps spot
> the ignition.
>
>
> http://www.flashbulbs.com/CrPDwnlds/FlashInfoPdf2Sm.gif
>
>
> Retina Roaster, Mike
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