Light beam reduction

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Chronos

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Optically speaking, it is a simple matter to convert parallel beams of light into a tighter [or looser] collection of still parallel beams. The resulting image merely changes in flux density. The number of photons involved is conserved - aside from the usual absorption and scattering losses.
 
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If the rays were exactly parallel (or originated from a true point source) the "volume in phase space" would be trivially zero, and "surface brightness" couldn't have any meaning.
 
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Chronos said:
Optically speaking, it is a simple matter to convert parallel beams of light into a tighter [or looser] collection of still parallel beams. The resulting image merely changes in flux density. The number of photons involved is conserved - aside from the usual absorption and scattering losses.
This is the heart of the confussion. If you can concentrate a beam of light, it should be brighter than otherwise. This, one would think, would allow us to increase the surface brightness of an extended object. But does it? It does improve point source brightness, but the facts say we can not for an extended object.

cesiumfrog said:
If the rays were exactly parallel (or originated from a true point source) the "volume in phase space" would be trivially zero, and "surface brightness" couldn't have any meaning.
This is a good point and you may want to apply it to a post I made on bautforum.com. I came here from there to seek further assistance. Fortunately, I found some! [BTW, THANKS! ]

It is a bit half-baked, but I wanted to throw it out before traveling - even though I risk greater criticism - rather than waiting till I return days from now. It attempts to demonstrate graphically why increasing surface brightness is doomed. [I have little hope left as a result. :frown: . Oh well. :smile: ]

Since I am traveling, I will simply link rather than polish it and repost here. http://www.bautforum.com/showthread.php?t=47121" is the thread there.

I hope you'll comment on it.
 
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