>
> chling@xxxxxxxxxxxx writes:
>
> << On the other hand I found using fresh alkaline batteries with
> longer charging time, the power is 0.2-0.3 stops higher than using Ni-cd,
> may be due to higher battery voltage.
> >>
> Charles,
> Some flash guns have a voltage control loop so the final flash
> voltage (after some time) is more tightly controlled and largely independent
> of battery condition. The Sunpak handle mount 522/544's are examples. As far
> as I remember the T32 does not use a feedback loop but the BG2 definitely
> does. So if you want more consistent flash output the BG2 should be your
> power source. The intermittent whine of the BG2 is as a result of the
> control loop stopping and starting the invertor. The control loop in the BG2
> uses a neon tube to start and stop the invertor based on breakdown voltage (
> a bit primitive). A redundant neon tube is used for safety. The Sunpaks use
> a zenner diode detector with a loop filter that causes similar hunting in
> the invertor sound. The Metz CT45 has no feedback but uses a different
> transformer tap for Alkalines and NiCd's. The battery chamber has an extra
> contact for the rechargeable NiCd pack which is different.
My T flashes whine by themselves. I thought it was a chopper for the stepup
circuit. The bounce grip is a lot louder.
>
> >>
> Does anyone have a flash meter want to join the test?
> <<
>
> I posted a very long rant about GN's (with measurements )
> a very long time ago to this list so it should be in the archives.
>
> Here are some of those old results repeated:
> Measured at 6ft (184cm) with Quantum Calcuflash meter
> Ratio
> (EV) GNmeas (ft) GN spec spec/meas
> T20 8*6 = 48 65 1.35
> Viv4600 13*6 = 78 100 1.28
> T32 13*6 = 78 104 1.33
This is exactly the value I got - for 2m. However, when I moved back
to 3m, the GN rose to the spec. because I started picking up bounce
from the room surfaces. For better or worse, all manufacturers use
room assisted values. Since I mainly use flashes in rooms, this doesn't
bother me. I'll just have to remember to downrate the flash by 2/3 stop
at 6' or less (or big spaces). I haven't really noticed the problem even
when using GN calculation because I use flash mainly for family snaps on
print film which has a large latitude. A worse practice in my view is to
boost the GN spec by making the flash have a narrow beam. Then you get
a flashlight effect, which is far worse than slight underexposure. You
also don't get softening bounce from the off-axis rays. The T32 is very
good on coverage, which is one reason its GN looks low compared to 3rd
party flashes. Even so, I use the wide diffusor.
> Sun522 13*6 = 78 120? 1.53?
> Sun544 7*6 = 102 140 1.34
> Sun5000/611 20*6 = 120 160 1.33
>
> So here the specified GN's were reasonably consistently
> 1.33 times larger than when actually measured in a dark
> walled, dark ceilinged room, and across 3 different vendor's flashes.
>
> Tim Hughes
> >>Hi100@xxxxxxx<<
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