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I think what Terry and Dunk are trying to put across is that there is a strong myth that has developed in some circles that a "fast scope" is better in terms of making a brighter image when used visually. So that will put the idea in some peoples head that you can substitute a small aperture fast scope for a large aperture slow scope. Or in other words an f5 is always "better" than a f10.
From a visual observing point of view that is simply not the case. A 10" scope is still a 10" scope and will put exactly the same number of photons on the focal plane regardless of it's focal length.
That is why I think it is very important when talking to beginners that we explain carefully what is meant by the term "fast" and "slow".
Malcolm
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