I just answered my own question from the recesses of my memory. The
difference is between a point and an extended light source. The wall is
an extended source and does not radiate in all directions as does a
point source.
Chuck Norcutt
Chuck Norcutt wrote:
> Sorry, but I still don't understand. If, in your first sentence, I
> replace "subject" with "light source" and "illumination of the subject"
> with "intensity from the light source" I have replaced subject with
> light source and the statement remains true.
>
> I'm still missing something very fundamental.
>
> Chuck Norcutt
>
> WayneS wrote:
>> At 11:41 AM 1/4/2009, Chuck wrote:
>>> <snip> What I don't
>>> understand is why, once the light has struck and reflected off the
>>> subject, why the subject is not treated as the "light source" for the
>>> reflected light that's emanating from it in the same sense as the sun is
>>> a light source.
>> The subject just gets smaller with distance. Hence there is less light
>> reaching the lens, but the illumination of the subject is the same, just
>> that its size in the frame is smaller.
>>
>> If it is the only subject, then an average meter would vary, but a spot
>> meter on the subject would be constant with distance.
>>
>> WayneS
>>
>>
>>
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