Re: [photo-3d] Re: Flash Photography help

["David W. Kesner" <drdave@xxxxxxxxxx>]

From: "David W. Kesner" <drdave@xxxxxxxxxx>

Dr. T. writes:

> What if you are shooting in a white bright room?
> Shouldn't you get the GN for a typical, instead of
> a dark environment?

No. I was talking about the "true" GN. That is the measure of 
the actual amount of light bouncing off a "standard" subject 
and returning to the camera. A reading taken in a small white 
room will include all the stray bounced light as well.

This should definitely be taken into consideration when 
choosing your exposure and adjusted accordingly. But think of 
it more as a filer-factor. The EV of a scene is the same 
whether you are shooting with a bare lens or with a 1+ ND 
filter. However, you need to compensate the exposure to factor 
in the filter. Same with flash. The GN of the flash is 
constant, however you need to compensate the exposure to 
factor in bounced or lost light.

For an example if you placed a black cat against a flat white 
background and a flat black backgound the flash exposure (for 
the subject) would be the same for both. However if you placed 
the cat in a white box and a black box, the flash exposure 
would be different as the white box would bounce and reflect 
more light to the subject.

That's all for now,

David W. Kesner
Boise, Idaho, USA
drdave@xxxxxxxxxx

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