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Re: [OM] even more about the F280 (long)

Subject: Re: [OM] even more about the F280 (long)
From: Jim Brokaw <jbrokaw@xxxxxxxxxxx>
Date: Mon, 22 Apr 2002 14:06:26 -0700
on 4/22/02 9:09 AM, Robert Swier at rswier@xxxxxxxxxxxxxxxx wrote:

> While the F280 manual is generally useless, it does provide enough
> information to definitively answer the questions on flash dumps and flash
> duration.
> 
> The manual is online at
> http://olympus.dementia.org/eSIF/omsif/flashphotogroup/manuals/f280.pdf, and
> this information comes from page 51.
> 
> Let's first look at the number of flashes you can get from a single set of
> AA alkaline batteries. The expected number of flashes are:
> 
> Manual: 80 firings
> Normal: 80 -- 600 firings
> SuperFP: 80 -- 260 firings
snipped a bit...
> <taking a deep breath>
> 
> I bought an F280 recently for fill-in flash on sunny days with hard shadows,
> and for a little extra light indoors with slow film. One thing I'll be sure
> of is to do a lot of testing before I start shooting with it for real!
> 
> Robert Swier
> Rochester, NY

It seems like everyone has got the variation in Super FP mode regarding
timing figured out... I think some of the reason it is confusing is that it
is possible and I think the battery durations indicated suggest that it is
likely the Olympus has setup Super FP mode to change the *amount* of current
dumped as well as the *length of time* over which that current is dumped.

A thyristor is an electronic switch, capable of acting very very quickly. In
a normal 'auto' flash, the thyristor cuts off the current flow *out* of the
capacitor (to the flash tube) when the flash circuitry receives a signal
that 'enough' light has reached the camera reflecting from the scene. This
signal can come from either a flash unit mounted sensor or from the TTL
sensor reading OTF. The flash fires, the flash tube reaches maximum light
intensity over a short but definite ramp of time, and then is cut off when
the sensor tells it.

Note that this ramp of light output doesn't affect the color temperature,
its not like a light bulb... the color temperature of the flash tube is
always 5800K due to the nature of the discharge, there is either enough
energy present to cause light in the ionized gas in the tube, or there is
not. But the initial -sufficient- energy will ionize only a part of the gas
molecules present; as more energy is input more of the gas reaches the
ionized state and discharges energy as light. But as the discharged energy
is an energy state change (quantum effect... help me out here, physicists!)
the light temperature is set by the gas molecule involved i.e. xenon).

In Super FP mode, the flash is 'strobed' to create a series of flashes
spaced so closely as to appear to be one longer flash... but those flashes
still have a ramp up to maximum intensity. If you flashed and then cutoff
before the maximum intensity of the flash is reached, then after some
microseconds flashed again, and again cutoff before maximum intensity of the
flash, you could effectively 'throttle' the output of the flashtube to some
lower than full-intensity output. The power you saved by cutting off during
the ramp-up would be available for the next flash ramp-up, and once the
entire duration (1/50th second?) has been covered any capacitor power
remaining would be there for shorter recycling or increased number of
flashes. This kind of quick power cutoff is well within the capability of
the thyristor, they can act *extremely* fast.

Here is some ASCII art of my theory...

Normal and auto flash

----------^^/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\--------------------
          |                                          |
         flash trigger     ...time varies...        quench signal

Super FP mode flash


---------^^/\/\--^^/\/\--^^/\/\--^^/\/\--^^/\/\--^^/\/\--^^/\/\------------
         |       |       |       |       |       |       |
        flash triggers repeatedly, ramps to full output
               flash time spans 1/50th second

low power output Super FP flash mode

---------^\--^\--^\--^\--^\--^\--^\--^\--^\--^\--^\--^\--^\--^\-------------
         |   |   |   |   |   |   |   |   |   |   |   |   |   |
        flash triggers repeatedly, quenches before full output
              flash time spans 1/50th second

We may need to ask an Olympus engineer to confirm the theory of operation of
Super FP flash (or is FP flash a Minolta invention licensed to Olympus...?)
but that is how I think the evidence points to its workings.
-- 

Jim Brokaw
OM-1's, -2's, -4's, (no -3's yet) and no OM-oney... 


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