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Re: [OM] Olympus Power Bounce Grip 2

Subject: Re: [OM] Olympus Power Bounce Grip 2
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Fri, 21 Aug 2009 14:58:39 -0400
OK, now I understand.  Our notation is just a bit different.  Trying to 
convert tenths of stops to actual focal rations requires too much 
playing with the square root of 2 so I just use 1/3 stop increments 
since that's all you can set the camera to anyhow.

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*.

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.

Your T32s are about 2/3 stop low at full power which compares favorably 
against the FL-50.  See, I think your FL-50 is not as accurate as you 
thought it was.  I've never seen a flash that was.  Trust but verify :-)

Chuck Norcutt




C.H.Ling wrote:
> 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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>>
> 
-- 
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