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  Previous versions of RustyBug's message #11182101 « silly inverse square law question. »

  

RustyBug
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Re: silly inverse square law question.


HelenB wrote:

The fact that the entrance pupil has a finite diameter allows it to capture divergent rays


+1 @ within the confines of the angles of inclusion, it can capture some divergent rays.

Hold on ... now, here's where the "Big Rub" comes with most all of this ...

ISL ... always produces divergent paths of light.
AI=AR can produce divergent, convergent or coherent paths of light.

The statement that reflected light travels iaw with ISL thus implies that reflected light is always divergent ... this is the part that I have my most ardent objection to.

Allowing light to continue its reflected path (predicated on AI=AR) iaw Newton's First Law of Motion ... yields that some of the light is traveling in divergent, convergent and coherent light paths (i.e. the array that I spoke of way back). The rest follows suit as the light that reaches the entrance pupil (angles of inclusion) and passes on to the film plane, accordingly.

Changing the camera position will have no effect on those rays that are traveling coherently, It will have some effect (angles of inclusion) on those traveling divergently and convergently. It isn't an ISL offset that retains the exposure irrespective of camera - subject distance ... it is the tradeoff of reduction of divergent paths, simultaneous with an increase in convergent paths (or vice versa) that occurs when camera-sujbect distance is varied (on axis).



Dec 11, 2012 at 01:13 PM



  Previous versions of RustyBug's message #11182101 « silly inverse square law question. »