At 3:21 AM +0100 2/23/04, Listar wrote:
>Date: Sun, 22 Feb 2004 16:27:57 -0500
>From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
>Subject: [OM] Re: Flash photography
>
>
>
>Joe Gwinn wrote:
>
> >>From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
> >>Subject: [OM] Re: Flash photography
> >>
> >>One slightly disconcerting outcome of this experiment was that I tested
> >>two T-32's and both gave me the same results with the flash meter.
> >>However, both were a full stop below what would have been indicated in
> >>the straight-on shots using guide number instead of the meter. Don't
> >>know why yet.
> >
> >
> > I would guess that it's the angular spread: When shhoting straight on,
> the light from the flash spreads out only enough to fill a 35mm frame
> using a 50mm lens. When the flash bounces off the ceiling, it instead
> spreads out in all directions, and so most goes the wrong direction and
> so is lost to the process, even though white paint has ~90% reflectance.
> >
> > Joe Gwinn
>
>Actually, a T-32 has enough spread to cover a 24mm lens within its
>stated guide number. The loss of light due to extra distance and less
>than perfect reflectance is well understood but what I didn't understand
>is why my T-32's are both measuring a stop below what they should be
>when not bouncing off anything. I was deliberately waiting 20-30
>seconds after the ready light to make sure they were full charged. I'll
>have to do some more testing.
If you can measure the voltage on the flash capacitor, do it. It should be
something like 330 volts DC. Stored energy in watt-seconds (joules) is
computed as (0.5)(capacitance)(voltage^2), so if the voltage is 235 volts, the
power will be down to one half, a one-stop loss. The other possibility is that
the flash capacitor is failing, but the more common failure mode is to become
shorted or open.
Joe Gwinn
The olympus mailinglist olympus@xxxxxxxxxx
To unsubscribe: mailto:olympus-request@xxxxxxxxxx?subject=unsubscribe
To contact the list admins: mailto:olympusadmins@xxxxxxxxxx?subject="Olympus
List Problem"
|