On Tue, 10 Nov 1998 00:53:46 -0800, "Jeffrey A. Hawkins" wrote:

>Of lens reversing, extension tubes, and the very high quality (two lens)
>diopters, what are the advantages and disadvantages of each?

Oh, where to start....? ;-) (BTW, add teleconverters to the mix...).
What is preferable depends very much on the particulars.
Starting with wide-angles, there is little option but teleconverters,
which, when added to close-focusing wides, can give passable
low-magnification macro results. Reversing wides on SLR's gives
very high magnification, but the auto-diaphragm is lost. Quality
can be reasonably good. Fast (faster than about f1.7) normal lenses
don't generally work well for close-up use, but slower normals
can be excellent with tubes, achromats (2-element diopters...),
and telecoverters (or combinations) - or reversed. Short teles can
also work well with these (but not reversed), though asymmetrical
designs may not be very good on tubes. With longer tele lenses,
tubes become less effective and achromats and teleconverters
more effective and practical for increasing magnification.
With zooms, the best solution is generally an achromat (zooms
often become unsharp on tubes, are often impractical to reverse,
and aren't any too sharp on teleconverters...). With any of
these solutions (except reversal of wides, since you will hit
diffraction limits too soon...), sharpest results may occur
at f11-16 marked stop (the effective stop may be far smaller...).
Using a TTL flash (mounted with the head at the lens end and
aimed at the subject) can provide nice light and greatly simplify
macro shooting. BTW, you can find some high-magnification
"hand-held" macro work on my web page, under "photographs", "Bugs".