There are a couple of different types of binocular loupe the most
common one is the galilean type which Rio has in their new catalog
these are very much like a standard loupe in that they have several
lenses lined up in one axis and give much better quality of
magnification at a longer focal length than the Optivisor type of
magnifier. They do have a couple of drawbacks they do tend to create
some distortion around the periphery of the lens and some spherical
distortion.
There is a second kind of binocular loupe that is the prismatic kind
they have a similar group of lenses but also include a prism like
many binoculars this allows a longer distance between elements and
results in a better quality magnification. These are sold by Zeiss
they are much better optically in that the field of view is larger
and it is much less distorted. however they are much more expensive.
They cost about as much as a microscope but they have one great
advantage over a microscope they are always pointed at what you are
looking at whereas with a microscope you must align your work and
body to the microscope. If you only need 4x magnification (about
equivalent to a #10 Optivisor) I think you will find a set of
prismatic binocular loupes is much better than a microscope however
if you need 10X magnification like some high precision engravers or
stone setters you may want the microscope.
I have had a set of Zeiss prismatic loupes for several years now and
would not part with them for the world.
If you are seriously interested in them contact Clemencia Sanchez at
Zeiss 888.733.2790 they will send you a set to evaluate for 30
days.
Disclaimer I am not connected to Zeiss just a satisfied customer.
Jim