No other sources, that's just me, made about 5 of those condensers last winter; confirm the weird NA 1.4, more or less measured and tested; but in that case the specimen is better to be mounted between two coverslips, that is a discrete hassle; for me was ok since I had to make two-coverslip mounts for a previous project. So the design published has lower NA but can work with a normal slide. There were some extreme condensers in the past, like "Nelson-Cassegrain" that could be used with NA 1.3 objective, but I haven't seen one for real.
Test of one model: https://www.microbehunter.com/microscop ... 28&t=14923 the apertometer says max NA~1,38 but an objective Zeiss 60x 1.40 gives darkfield (maybe they were cheating too about NA? Or the apertometer scale is a bit off).
Anyway I couldn't see astonishing improvements in resolution. Maybe with "all ducks in a row" and less vintage optics.
If somebody wants to try, I can send one or make some new to fit the condenser mount.
That may work with the specimen in water? I tried briefly with no success. Or if we get a slide made high refractive index glass...