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Acropolite,
When I did my sig I wasn't aware that I could use the normal V.Bulletin control codes in it, so I used the standard capital F used in many photographic forums to denote Focal Ratio.
Excellent point re focus, which derives from the latin word fo "hearth" (fireplace). Now I'm no expert in Latin though I did study it many years ago, however , the lingua franca of science was Latin and in many cases the likes of Sir Isaac Newton, Francis Bacon and so on derived new meanings based on concepts as much as the meaning of the word, thus while a hearth may at first have no apparent connection to the focal point of an optical system, both are the centre of attraction and focus of the energy of light. Feel free to toss in a more accurate method of explaining it.
Black holes and professional astronomers, oh what fun! Professional astromers are, like many other scientists and researchers faced with an intriguing problem of having to explain in lay terms what is often highly bizzare and difficult to decribe in nature so they use metaphorical descriptions. The term was coined by Jophn Archibald Wheeler to describe what was previously known as "frozen stars", again a term used to try to convey what is in reality a highly complex piece of mathematical and cosmological theory. Thus we have all sorts of interesting analogies (pizza shaped galaxy groupings, sausage strings blah blah blah) in astronomy as often mere words cannot convey the theory in a reasonably easy to understand way.
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