As you know, a magnification-reducing auxiliary lens increases the working distance of a stereo microscope. Here's how I got 40 mm more working distance...
There is no 0.7x lens on the market for the Bausch & Lomb Stereozoom, so I designed one. To be precise, I designed a lens to go in the cell in place of my 2x lens (which I never used) and was prepared to have an eyeglass maker make it, but then found the exact thing on Surplus Shed. More here...
http://www.covingtoninnovations.com/michael/blog/1911/index.html#x191120