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Re: [OM] Olympus Power Bounce Grip 2

Subject: Re: [OM] Olympus Power Bounce Grip 2
From: Tim Hughes <timhughes@xxxxxxxx>
Date: Fri, 21 Aug 2009 23:31:46 -0700 (PDT)
If somebody has access to ISO standards through their work , they might look up 
the description of how to perform these GN tests according to ISO standards:

ISO 2827:1988
Specified are methods of measurements and standards of performance for
light output, angle of coverage, ready indication, recycle time and
number of flashes for electronic flash equipment of the single flash
type, which is primarily intended to provide illumination for
photography with cameras in which the contacts that control the flash
are closed when the camera shutter is fully or nearly fully open.

And also less useful:
ISO 1230:2007 specifies the definition and determination of the ISO guide 
number of electronic flash equipment. It does not specify the definitions and 
measuring methods for the light output of electronic flash equipment, which are 
specified in ISO 2827.

Tim Hughes


--- On Fri, 8/21/09, C.H.Ling <ch_photo@xxxxxxxxxxxxx> wrote:

From: C.H.Ling <ch_photo@xxxxxxxxxxxxx>
Subject: Re: [OM] Olympus Power Bounce Grip 2
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Date: Friday, August 21, 2009, 6:55 AM

The GN I shown here is the claimed one displayed on the flash. For the
reading I expected you know very well as we both have Sekonic, example F4
0.5 means 1/2 stop between F4 and F5.6. For the results, e.g. GN40 at 10
feet distance, the right reading should be F4.... anything not match is
deviation but it need some math to calculate the actual GNs for the 'non
standard' values.

C.H.Ling

----- Original Message ----- 
From: "Chuck Norcutt"

>I don't understand the numbers in your table.  I would have expected to
> see a single pair of numbers for each zoom and power setting, eg:
>
> 35mm claimed GN actual GN
> ---- ---------- ---------
> full GNc GNa
> 1/2 --- ---
> 1/4 --- ---
> etc.
>
> What did you give me?  Does 0.1, 0.7, etc. mean deviation in stops from
> the expected exposure?  If so, all deviations are positive?  Too much
> light?
>
> Chuck Norcutt
>
>
> C.H.Ling wrote:
>> Just got the Sekonic 328F back from my friend, he borrowed it some months
>> ago for playing with his new home studio.
>>
>> Here is the result I got, flash to meter distance 10 feet, ISO100,
>> 1/125s:
>>
>> FL-50
>>
>> Zoom setting: 35mm
>>
>> GN30 - F2.8  0.1
>> GN42 - F4
>> GN59 - F5.6  0.1
>> GN84 - F8     0.1
>> GN118 - F8  0.7 (full power)
>>
>> Zoom setting: 85mm
>>
>> 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)
>>
>> T-32A
>>
>> GN52 - F4 0.6
>> GN104 - F8 0.2
>>
>> T-32B
>>
>> GN52 - F4 0.2
>> GN104 - F8 0.2
>>
>>
>> C.H.Ling
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Chuck Norcutt"
>>
>>> Anybody with an FL-50 got a meter?  How accurate are the guide numbers
>>> at various power levels and zoom settings?
>>>
>>> Chuck Norcutt
>>>
>>>
>>>
>>> C.H.Ling wrote:
>>>> Sorry for mis-read your point, the GNs on older flashes might be not
>>>> accurate and mostly under powered but the FL50 seems much better. On
>>>> the
>>>> field it is not easy to reach a very accurate fill due to time limit,
>>>> sometimes I just use TTL with -1 flash compensation. I'm also not good
>>>> in
>>>> estimate distance but anything in the 0.5 stop error range is ok with
>>>> me.
>>>>
>>>> C.H.Ling
>>>>
>>>>
>>>> ----- Original Message ----- 
>>>> From: "Chuck Norcutt"
>>>>
>>>>> How does any of this relate to the subject of my comment which was
>>>>> that
>>>>> flash units tend to be underpowered with respect to guide number?  My
>>>>> statement means if you use guide number in your calculation your shot
>>>>> will be slightly underexposed.  That's all.  I meant nothing with
>>>>> respect to various exposure situations.
>>
> -- 
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