[OM] Re: fashion and ringflashes; watt-seconds of the T8

Subject: [OM] Re: fashion and ringflashes; watt-seconds of the T8
From: Joe Gwinn <joegwinn@xxxxxxxxxxxx>
Date: Wed, 6 Feb 2002 09:35:15 -0500
At 10:18 PM +0000 2/5/02, olympus-digest wrote:
>Date: Tue, 5 Feb 2002 14:15:43 -0600
>From: "Sue Pearce" <bspearce@xxxxxxxxxxxxx>
>Subject: [OM] Re: fashion and ringflashes
>"Just for fun, do you know the guide numbers, to compare with the T8 and
>T10, which are 8 or 10 (meters, ASA 100)?  Maybe that's how the Olympus
>ringflashes were named?"
>Here we go again, I almost hate to bring up the subject of watt seconds.
>These things are generally reflectors that accommodate any strobe head of a
>given system, although I think there are some with permanantly attached
>flashtubes. Like all pro strobes with separate powerpacks, there are no
>published guide numbers. This is a quick way to tell commercial and
>industrial guys. Few know GN's. The head is attached to a powerpack,
>anywhere from 800WS to 4000 or more, so there would have to be too many GN's
>to remember. Most fashion guys who use these have an assistant to hold the
>flash meter, and another to pop the flash.

These things probably allow f/11 at 1/250 second, or better.  

I lack the assistants, but I do have the flashmeter.  It's been really useful 
over the years.

>If I had to guess, I would think that they are used anywhere from as low as
>25 or so WS up to around 200. This, of course, depends a lot on the
>reflectivity of the individual reflector, and depth of field requirements. A
>lot of times, DOF is shallow, so it would be low. I have seen where it is
>used as a sole light. (That's just one, not for the feet)
>As a comparison, the OM flash would be probably less that 10 WS. What I
>don't like about the T8 is that it is not very useful past about 8". I would
>like to use it as a fill out to several feet.

Well, I couldn't resist measuring it.  I measured the relative optical flash 
energy of a T-10 on manual and of a Sunpack Auto 433D, also on manual.  The 
Sunpack has five times the optical energy output of the T-10.  Then, I 
carefully took the flashtube end of the 433 apart and measured the voltage on 
the flashtube (346 volts and creeping up), and read the size of the flash 
capacitor (1050 microfarads).  Doing the math, we get (346^2)(1050e-6)/2= 62.85 
joules, call it 63 joules.  One fifth of this is 12.57 joules, or about 13 
joules.  So, you aren't far off in your estimate of 10 or less joules.  (Joules 
are the SI energy unit equivalent to watt-seconds.)

The Vivitar 285 I had many years ago was 50 joules, also measured by me.

An Ultra 1800 studio flash puts out ten times more optical energy than the 
Sunpack 433, so the 1600 is about 630 joules, assuming equal efficiency in 
conversion from electrical to optical energy.  The manufacturer, Paul C Buff 
(<http://www.white-lightning.com/>), claims high efficiency, so the 
efficiencies may not be equal, but Buff's X1600 and UltraZAP 1600 units claim 
660 joules, and 630 is pretty close to that claim, well within the margin of 
error (1/3 of a stop) of my optical energy measurements.  One third of a stop 
is a ratio of 1.26.

Warning.  If anybody is tempted to take flash units apart and measure them, as 
I have done, be very careful.  Getting hit with 50 or 60 joules is enough to 
stop the heart and/or break bones, never mind 600 joules, and significant 
chargemay  remain on the main capacitor even when the unit is off.  (Heart 
defibrillators deliver about 400 joules per pop.)  Studio units are 
particularly dangerous because all flash capacitors will recover significant 
charge even after being fired, for reasons too long-winded to explain here, and 
the studio units are big enough that the residual charge is sufficient to throw 
you across the room.

Joe Gwinn 

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