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.
>>
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
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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