The meter was triggering the flash via an attached radio transmiter. My
meter has a built-in Pocket Wizard transmitter but I don't have a Pocket
Wizard receiver.
You're probably right that there's some delay involved but I'm surprised
nevertheless. I'll have to re-do the test sometime using a cable.
The 1/3 stop variance I referred to was a 1/3 stop variance between two
different 285's, not a 1/3 stop difference from the spec. The higher
powered one is three years old and the other about 15 years old. I was
measuring the 285's from a distance of 10 feet. Makes it easy to
compute that a reputed guide number of 120 should yield f/12. I also
tried my Sunpak 422 with guide number 100. All gave me a reading of f/8
to f/8.1 at max power. Both 285's are measuring a full stop or more
below their spec'd output and the 422 is measuring 2/3 stop below its
spec. Despite the guide numbers the 422 and 285 are really pretty
equal. The 285's 120 guide number drops to 100 when set for 35mm lens
coverage which makes it the equal of the 422 which has guide number 100
and 35mm lens coverage.
I ought to measure the T-32's again just for completeness.
Chuck Norcutt
AG Schnozz wrote:
> Chuck,
>
> I've been thinking about this a little bit. (too little as
> you'll soon read).
>
> Did you use the meter to trigger the flash? Or did you have the
> meter in "capture" mode? When used as the trigger, I believe
> you are correct in that the "shutter speed" of the meter was
> trimming off the flash exposure. This is not uncommon when using
> radio and optical slaved strobes where there is a slight delay
> before all of the flashes are triggered. What happens is the
> duration of the flash, which is normally within the 1/500 window
> is actually skewed and part of the flash dump occurs outside the
> 1/500 window.
>
> My Poloris flash/ambient meter doesn't seem to be affected by
> this as much as I've seen the Minoltas affected. Hmm. I wonder
> if the flash meters are getting discontinued????
>
> I asked about 18% vs 13% because the incident domes are
> published as 18% equivelent. If this is true and the
> manufacturers are utilizing 13% to determine guide number, then
> I'm thinking that this would account for the 1/3 stop variance.
> Unless my math is wrong and it's actually the other way around.
>
> I revisited this last night and found that my 285HV truely was
> putting out the published amount of light. One big problem with
> the 285HV, though, is the zoom head does not produce a uniform
> pattern of light. To illustrate this, take your flash and A1
> out to an empty parking lot at night and fire the flash at full
> power with the different zoom positions. Have the A1 on manual
> exposure mode and use a much wider zoom position on the lens so
> you can see the entire flash pattern.
>
> The 285HV's pattern at 50mm setting can have more than a
> half-stop variance across the designated FOV. At the wide
> settings, I get over one stop variance. This is why I only use
> the flash with diffusers unless I'm shooting over 50 feet away.
> As soon as I saw the pattern and falloff I started searching for
> an affordable barebulb flash. (still looking).
>
> AG
>
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