From: Carl Weese (cweese@earthlink.net)
Date: 12/12/01-08:13:39 AM Z
Daren,
Not absurd at all: the inverse square law does *not* apply when using a
softbox in the usual way for 'soft' lighting effects. That is, where the box
mimics an artificial overcast sky over the subject. (Or window next to it,
etc, etc.) If a two-by-four foot softbox is used 2 feet from the subject,
inverse-square light falloff will not be observed when moving it six inches
in or out. If it is used ten feet from the subject it will become an
effective point source and roughly obey the inverse square law--and of
course at that point the softbox serves no visual purpose and only wastes
light.
---Carl
--
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and workshop information at:
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----------
>From: Daren <mdaren@uswest.net>
>To: alt-photo-process-l@sask.usask.ca
>Subject: Re: uv ballast ground, yes
>Date: Tue, Dec 11, 2001, 6:19 PM
>
> Sandy,
>
> If what you have just stated is true then when shooting with my softbox
> the inverse square law shouldn't apply?? That's absurd!! And what about
> flourecent banks used for lighting?? Are these not effected by inverse
> square law??? Something is more than a bit fishy here.
>
> Light falls off at a regular rate regardless of relative distance and
> size of light source to subject (point source vs. soft source). The
> idea that a soft or broad source will create light in any way different
> than a point source is wrong. Light is light, we obviously have
> different wave legnths in the elctromagnetic spectrum, but a photon is
> just a photon. The photon doesn't know the difference between "soft",
> "hard", "bright" or "dim", it is simply a photon. Besides, the ONLY
> difference between a point source and a soft source is distance from
> source to subject and size relative to one another. Unless acted upon
> by a great force (large amounts of gravity) or another substance (glass,
> etc.) light has no "choice" but to obey the laws of physics, that
> includes the inverse square law. Light is not magic, it can and must be
> described in a rational way.
>
>
> Sandy King wrote:
>
>> Robert,
>>
>> The inverse square law only applies to point source lights. I knowfrom
>> experience that it does not apply to banks of fluorescent tubes when
>> used at typical exposing distances of 2-6".
>>
>> I can not give you the math or optical laws for this, however, there
>> was a thread on this subject on the list some time ago, perhaps a year
>> or more? At this point I don't know how to search the archives and
>> hope that perhaps someone else can direct you to the thread.
>
>
>
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