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Re: [OM] Be careful where you sit...

Subject: Re: [OM] Be careful where you sit...
From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
Date: Mon, 5 Jan 2009 11:24:00 +0800
Not only 'point source' is governed by inverse square law, any light source 
that is not parallel beam or better say any divergency light souce apply the 
inverse square law.

The light reaching the camera will NOT drop with distance if the scene is 
evenly illuminated and covered the whole focusing screen (i.e. the whole 
metering area). Unless there is strong hazy in between the object and 
camera.

In your case the person may be a bit far away from the backdrop, the light 
fall on the person is stronger than the backdrop so when you move the camera 
away, the area of the person filling the camera is reduced so the meter read 
less light (because of the average metering causes error).

C.H.Ling

----- Original Message ----- 
From: "Andrew Fildes" <afildes@xxxxxxxxxxxxx>


> I'm having trouble with this one as well.
> In the studio, if I use a soft box, it's hardly a 'point source' but
> its output is governed by the inverse square law (thank goodness, as
> i have a couple of old non-adjustable heads).
> Again, I have noticed that if i move the camera position well back
> and nothing else, from an evenly lit subject such as a person against
> a backdrop with a similar tone to skin, then there seems to be a drop
> in the light reaching the camera.
> This made sense to me - why should there be any difference in the
> behavior of light emitted and light reflected? - photons are photons.
> Never really bothered to check it - I just check the histogram every
> time I change a set up significantly - but it seems to make sense.
> But then of course, using an incident light meter makes nonsense of
> all that too.
> Bugger - I'm confused.
> Andrew Fildes
> afildes@xxxxxxxxxxxxx
>
>
>
> On 05/01/2009, at 5:19 AM, WayneS wrote:
>
>> The difference is not about the subject being the light source
>> but rather the subject is illuminated, hence its intensity is what it
>> is. Just because the photographer is further from the subject
>> does not change its illumination.
>

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