In article <31DC5152.46A@logica.com>, humphreyd@logica.com says...
[most deleted.....]
>No matter what close-up lens it is that you choose, there will be
>_some_ image degradation, simply because you're putting (at least)
>one extra glass element between your subject and the film.
>However, most manufacturers and many independents produce Extension
>Tubes which do much the same job as the close-up filters, except there
>is no glass element involved; you're simply increasing the distance of
>your lens from your film, allowing larger magnification and smaller
>focussing distances. [...]

I would not assume that a no-glass extension tube is necessarily
optically superior to a close-up lens. Almost all lenses show
variation in optical performance with focus distance, and some
short telephoto designs are particularly bad in this respect,
but can perform very well with 2-element achromatic close-up
lenses by mid apertures.
Hope This Helps