Olympus-OM
[Top] [All Lists]

Re: [OM] Flash guns for OM4T

Subject: Re: [OM] Flash guns for OM4T
From: "Jim Sharp" <jsharp@xxxxxxxxxxx>
Date: Fri, 22 Sep 2000 11:51:59 -0500
I did some similar tests with my Vivitar 283 when I first got my flash meter a 
long time ago. Curiosity 'ya know... From 8' to over 25' in my home, using the 
auto sensor on the flash, the 283 was always within 1/2 stop of the auto sensor 
setting. I tried all of the auto sensor settings plus the manual setting and 
the results were always the same... Right on +- a tiny bit. My flash meter only 
has 1/2 stop resolution so I figured I was at the measurement error threshold. 

My house is a ranch with low, light ceilings so this may have helped. The flash 
has always exposed correctly in use so I was satisfied with the equipment, and 
the test. You can add that to the data pile...

And to repeat what was correctly stated before...

The whine you hear on the flash unit is the inverter circuit ( an oscillator ) 
converting the low voltage input to the 400-500 volts needed to fire the tube. 
Notice how units like the Honeywell handle types, Vivitar 283, 285HV, etc. make 
no noise when running on an AC adapter. That's because the external AC 
transformer provides the needed high voltage. No need for the inverter circuit. 
The 283 units on batteries have additional circuitry to keep the storage 
capacitor voltage constant. Once the flash is up to full charge the whine is 
not constant. You are hearing the circuit cycle on and off to regulate the 
voltage. 

I wasn't aware that the bounce grip did this but it's just one more reason I 
need to buy one soon - for the T-32 I also need to buy :-)

>From my limited experience, I don't like the zoom type flashes either. They 
>have less coverage in order to inflate the guide numbers, and you end up with 
>properly but harshly exposed subjects and not enough background illumination. 

Just my $.02

--
Jim

>> 
>>  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<<
>
>< This message was delivered via the Olympus Mailing List >
>< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
>< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
>

< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz