Unless something really compelling comes along, this will
be my last physics of flashing post. :-)
george <george@xxxxxxxxxxxxxxxxxx> wrote:
> describe below, but something doesn't 'feel' right to me. I think the
> inverse square law applies to a 'point source' of light, which a single
> flash approximates. But when one starts placing more flashes in the
> picture, I'm just not sure the effect is additive. To carry this a step
>
Yes, the inverse square law really only holds for a point source.
In the limit of an infinite area light source, the distance does
not even matter. However, compared to the length of a football
field, N t32 flashes (where N is the number you can afford) will
probably cover a rather negligible extent so the point source
approx should hold...
But you're right -- 4 t32's probably wouldn't give a good exposure
across a football field. That is because (1) the GN is rated for
f/1 and you'll be lucky to be using an f/2.8 lens and (2) GNs are
really white lies and generally assume nice indoor conditions
with lots of light bouncing off the walls and all that.
As far as dependence on the size of the object being illuminated,
that should not matter -- you already account for that by virtue
of its covering a smaller or larger area in the viewfinder. If
it covers the whole viewfinder, it contributes more light to the
average reading, but that doesn't change how that region will
be exposed.
Anyway, I am going to stop now because I'm sure that everyone has
had enough of these lists. I'm enjoying thinking about it, though,
so if anyone wants to talk more about this (especially if I'm
somehow confused and wrong), give me a ping offlist.
:-)
joey
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