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  Previous versions of Access's message #11185589 « silly inverse square law question. »

  

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Re: silly inverse square law question.


I vaguely remember this kind of thing from my physics teacher who explained that inverse square was from a perfect point source and that a perfect linear source would be 1/r and a perfect planar source would be 1.

And that most light sources we have today (in reality) are somewhere in between these three, for instance an incadescent bulb or the sun might be close to a point source (though the sun being so far away, our inability to change our relative distance toward/away from it), a flourescent lamp, somewhere between a point source and a linear source (depending on it's relative length and dispersion), and once you start playing with reflections and lenses then you can create things that are closer to planar sources; like the beam of a perfect flashlight that spreads out only slightly over a long distance.

In photography you have another issue of importance, relatively light source size. An object like a softbox or umbrella, creating a large light source that is diffuse enough, it will illuminate a given point on the subject from multiple directions, which is desireable.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
click on 'light on vision'
Overall it's a very useful resource, though a bit dated.

10 pages of 'discussion' that one does not have time to read, really people ought to learn the skill of applying knowledge and then just take it from their. There is no need to debate, or even explain, neither of these things changes reality; our only real use of knowledge is to _apply_ it to what we do, in this case, photography.



Dec 12, 2012 at 04:57 PM
Access
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Upload & Sell: Off
Re: silly inverse square law question.


I vaguely remember this kind of thing from my physics teacher who explained that inverse square was from a perfect point source and that a perfect linear source would be 1/r and a perfect planar source would be 1.

And that most light sources we have today (in reality) are somewhere in between these three, for instance an incadescent bulb or the sun might be close to a point source (though the sun being so far away, our inability to change our relative distance toward/away from it), a flourescent lamp, somewhere between a point source and a linear source (depending on it's relative length and dispersion), and once you start playing with reflections and lenses then you can create things that are closer to planar sources; like the beam of a perfect flashlight that spreads out only slightly over a long distance.

In photography you have another issue of importance, relatively light source size. An object like a softbox or umbrella, creating a large light source that is diffuse enough, it will illuminate a given point on the subject from multiple directions, which is desireable.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
click on 'light on vision'
Overall it's a very useful resource.

10 pages of 'discussion' that one does not have time to read, really people ought to learn the skill of applying knowledge and then just take it from their. There is no need to debate, or even explain, neither of these things changes reality; our only real use of knowledge is to _apply_ it to what we do, in this case, photography.



Dec 12, 2012 at 04:56 PM
Access
Offline
Upload & Sell: Off
Re: silly inverse square law question.


I vaguely remember this kind of thing from my physics teacher who explained that inverse square was from a perfect point source and that a perfect linear source would be 1/r and a perfect planar source would be 1.

And that most light sources we have today (in reality) are somewhere in between these three, for instance an incadescent bulb or the sun might be close to a point source (though the sun being so far away, our inability to change our relative distance toward/away from it), a flourescent lamp, somewhere between a point source and a linear source (depending on it's relative length and dispersion), and once you start playing with reflections and lenses then you can create things that are closer to planar sources; like the beam of a perfect flashlight that spreads out only slightly over a long distance.

In photography you have another issue of importance, relatively light source size. An object like a softbox or umbrella, creating a large light source that is diffuse enough, it will illuminate a given point on the subject from multiple directions, which is desireable.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
click on 'light on vision'
Overall it's a very useful resource.



Dec 12, 2012 at 04:51 PM



  Previous versions of Access's message #11185589 « silly inverse square law question. »