>> Forgive me if I'm missing something obvious, but
>> if it's accepted that
>> there is a formula for producing a correct flash
>> exposure (e.g. ISO rating
>> + subject distance = X amount of light for correct
>> exposure) couldn't the
>> flash calculation simply be linked to the lens'
>> focus distance so that
>> whatever you focus on is correctly exposed, rather
>> than relying on the
>> amount of light coming back into the lens....
> From: Bob Meyer <[EMAIL PROTECTED]>
> It falls down simply because it doesn't account for
> the varying reflectivity of different subjects. A
> black man in a white shirt, for example, could end up
> with the shirt overexposed and the skin tone
> underexposed.
But surely if you stood a black guy in a white shirt next to a white guy
in a black shirt, the amount of light needed to give a correct exposure
would be the same - just as if the black guy was wearing a black shirt and
visa versa.
Using studio lights, if you have measured the amount of light falling on
a subject using a hand-held meter, you don't change the lighting if your
subject changes clothes. The same amount of light is still falling on them.
Reflectance of skin tone and clothes is only an issue with TTL meters, where
you are measuring the amount of light reflecting back from a subject, rather
than the light that falls upon them. This causes under-exposure if their
clothes are too reflective, by fooling the meter into thinking the scene is
brighter than it really is.
My original point was that by linking the flashs' output to the lens'
distance scale, you could bypass the TTL meter and reflectance of subject
wouldn't be an issue.
However, I think my point only stands up when flash is the only light
source. I think it could get complicated when you are trying to balance
ambient light with flash, when you would need to use the TTL. Maybe in those
situations TTL could be used to set the ambient exposure, and the snapper
would have to manually dial the flash down by 1-2 stops depending on the
amount of fill needed?
--------------
James McCauley
[EMAIL PROTECTED]
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