|
Markus
The thing to remember is that a camera lense is a complete system, an eyepiece is only part of a system, it only works when attached to a telescope. Also by definition, a camera lense is only used for imaging, while an eyepiece is (normally) only for visual use. Camera sensor accumulate signal while eyes don't so "speed" is more important in a camera lense than in an eyepiece.
Speed is more important in terms of the telescope being used. There is sometimes confusion about the relevance of the speed of a scope to a visual observer. For an imager, speed is a relevant factor as a faster scope will give you a brighter image. For a visual observer, it is less important, although a "faster" can give benefits in terms of portability, not having to climb a ladder etc. As a visual observer I am more interested in the raw numbers, aperture and focal length as that gives me an idea how bright(determined by the aperture) and large it is (determined by the focal length) for a particular eyepiece. Speed in terms of f ratio is a handy shorthand for me if combined with the size of the scope. For example if I see 20" f5, I know my 17mm eyepiece will give me 150x and that's what I want to know.
With zooms, I have never used one but there are people who do and love them. As with camera lenses it is very hard (impossible? maybe or at least very expensive!) to make a zoom that has no aberrations across its entire range. They exist for the same reason that zoom lenses exist, the convenience outweighs any issues.
Malcolm
|