This Korean link shows how wildly some modern flash hardware varies from ideal
GN and not just at max output:
Not sure if link will work as it has Korean characters that may nor work in
text mailer
http://www.sfcc.re.kr/Attachment/4%EC%9B%94_%ED%8F%AC%EB%A5%B4%ED%88%AC%EA%B0%88-FLASH.pdf
Try using first english part, to find pdf if it does not work.
Unfortunately the text in pdf has slightly strange english, so difficult to
understand. The graphs are interesting though.
Unfortunately they do no spell out how the ISO flash test standard 2787 they
reference works. To get that standard will cost you $50, unless somebody has
acess through their work?
Tim Hughes
Tim hughes
--- On Fri, 8/21/09, Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
> Subject: Re: [OM] Olympus Power Bounce Grip 2
> To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
> Date: Friday, August 21, 2009, 7:49 PM
> Yes, CH, you are absolutely
> right. I am confusing f/11.8 in guide
> number calculations with the nomenclature on the Sekonic
> meters. In the
> guide number calculations f/11.8 is some small fraction
> away from f/12
> and not 0.8 stop up from f/11 or 80% of the way to f/16.
>
> Sheesh. It's time to go to bed. I think I'll do
> that.
>
> Dr. (sheepish) Flash :-)
>
>
>
>
>
> C.H.Ling wrote:
> > Hi Dr. Flash, F11.8 is equal to F11 +0.8 stop? So F12
> is equal to F11 +1
> > stop? then F12=F16??? The formula should be more
> complex than you think :-)
> >
> > C.H.Ling
> >
> > ----- Original Message -----
> > From: "Chuck Norcutt"
> >
> >> I was working from my head and could well be wrong
> but let's just take
> >> the 35mm GN118 example. At 10 feet GN118
> should yield f/11.8. The
> >> measured result was f/8 + 0.7 stops.
> Therefore the measured result is
> >> 0.3 stops short of reaching f/11. Yet the
> requirement is for 0.8 stops
> >> above f/11. Adding the 0.3 stops short of
> f/11 + the 0.8 stops yet to
> >> go sure sounds like 1.1 stops to me.
> >>
> >> Me thinks your math is wrong if you equate f/11 +
> 0.8 stops (meaning
> >> 8/10 of the way between f/11 and f/16) to
> f/11.2. It's actually
> >> somewhere between f/14 and f/16.
> >>
> >> Chuck Norcutt
> >>
> >>
> >> Ian Nichols wrote:
> >>> 2009/8/21 Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>:
> >>>
> >>>> for zoom setting 35mm you got
> >>>>
> >>>> GN30 - F2.8 0.1
> >>>> GN42 - F4
> >>>> GN59 - F5.6 0.1
> >>>> GN84 - F8 0.1
> >>>> GN118 - F8 0.7 (full power)
> >>>>
> >>>> At 35mm all of these up to full power are
> less than 1/3 stop error. But
> >>>> at full power you should have gotten f/11
> + 0.8. Instead, you got f/8 +
> >>>> 0.7 or *more than a full stop off*.
> >>> My gut feeling was that you were wrong there,
> Chuck, so I threw
> >>> together a quick spreadsheet, getting the f
> numbers for the fractional
> >>> stops by n*(2^0.05) - a half (i.e.
> square root) time a tenth- where n
> >>> is the next lower full stop number.
> >>>
> >>> The resulting table says that f/8 +0.7 stops
> is f/10.2 and that f/11.8
> >>> is f/11 +0.2 stops - only half a stop out.
> >>>
> >>>> for zoom setting 85mm you got
> >>>>
> >>>> GN29 - F2 0.9
> >>>> GN41 - F2.8 0.8
> >>>> GN58 - F4 0.8
> >>>> GN82 - F5.6 0.8
> >>>> GN116 - F8 0.8
> >>>> GN164 - F11 0.5 (full power)
> >>>>
> >>>> At 85mm GN29 is correct, GN41 is 1/3 stop
> low, GN58 and GN82 are 0.4
> >>>> stops low, GN116 is 0.8 stops low and
> GN164 is 0.9 stops low.
> >>> Similarly I make f/11.6 = F/11 + somewhere
> between 0.1 and 0.2 so
> >>> 0.3-0.4 stops low, and f/16.4 = f/16 +
> less than 0.1, so only about
> >>> half a stop low
> >>>
> >>> Didn't check the others because it was only
> those that looked wrong at
> >>> first glance. So one of us is working
> this out wrong. If it's me,
> >>> I'd like to get my head around what I'm doing
> wrong.
> >>>
> >>>
> >> --
> >>
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> >>
> >>
> >
> --
> _________________________________________________________________
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>
>
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