Ooops! See Tim's response. I forgot that even though the energy is
distributed between the two flashes the light power still has to add up
and the guide number should nominally remain at 28. Tim's response
undoubtedly explains the discrepancy between 28 and 22.
I'll have to consult Dr. Flash on adding the power of two light sources
before responding on these matters in the future. Dr. Flash adds that
if you had two flashes, each with guide number 28 then the resulting
guide number would be sqrt(28^2 + 28^2) = 39.6 or, since both lights
have the same power, more easily calculated as 28*sqrt(2)
Chuck Norcutt
Chuck Norcutt wrote:
> If the available energy to each head is cut in half (1 stop) then the
> guide number would nominally be reduced by the square root of 2.
> Dividing 28 by 1.4 I get 20 instead of 22. But I guess that's close
> enough.
>
> Chuck Norcutt
>
> Jeff Keller wrote:
>> The guide number is limited by the energy stored in the capacitors
>> and the width of field illuminated. If two heads are sharing the same
>> energy it seems reasonable that the guide no. would go down ... -jeff
>>
>> On 7/19/07, usher99@xxxxxxx <usher99@xxxxxxx> wrote:
>>> Piers, Thanks again for these.?
>>>
>>> Weird that on the Alan Wood site in one place near where he
>>> mentions the calculator panels (T28), the? GN with one flash is
>>> listed as 22 and 28 with 2 heads.? It is the opposite later on his
>>> site and anywhere else, including on your panel pdf.?? Must be a
>>> mistake on the AW site.? I don't know how the GN would go down with
>>> 2 heads (must be the case), unless the controller T power control
>>> attenuates the power to both.? Perhaps there is something weird
>>> about GN's at macro distances.? Manual macro flash shouldn't be as
>>> weird as quantum effects, though Heisenberg seems to lurk over my
>>> shoulder when I try it.
>>>
>>> http://www.alanwood.net/photography/olympus/t28-macro-twin-flash.html
>>>
>>>
>>> Mike
>>
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