I have, personally, not come across an axial iris and ...
It is really just two irises stacked on top of each other. The lower, and larger, is a slightly modified abbe iris from an old abbe condenser. The Axial iris is much smaller (V. 3.0 is about 13mm wide, 4.0 will be about 11mm wide.) than the larger iris, but the two do not touch each other.
The smaller iris is built up on clear plastic sheets so that light can get by it.
Do you think that the 1955 approach by Galbraith could be used in conjunction ...
I have not heard of this device before today, and I followed your link, but that didn't tell me much either. Version 2.0 used 'tombstone' filters, which 'work', in that you do get a Rheinburg effect. What makes the Mikropolychromar different is that you can control glare, and DOF which yeilds much more consistant results.
Rheinburg is similar to DF, in that too much glare diminishes IQ. With DF, you can control that by building a 'thin' slide, and or reducing debris on the slide, and or reducing smears, fingerprints, etc on either the slide or cover slip. Those techniques work well with the MPC, and having an iris to help control glare goes along way in improving IQ.
The smaller axial iris controls DOF (and therefore contrast), just the way your iris in a brightfield condenser does. With the old tombstone filters, their was no easy way to adjust the size of the inner stop. Having a small diaphram really makes a big difference in IQ.
This condenser I've built works best when oiled (like a DF condenser), and can be used as a DF condenser. (Although I like my dedicated DF condenser better) It can also be used as a BF condenser (Although I prefer my dry dedicated BF condenser better).
My MPC condenser is centerable (an old DF condenser mount). Ziess' wasn't centerable, even though it used an Aplanat 1.4 condenser. Ziess' worked well as an oblique condenser, simply because the device could be swung aside on the light path. So far, I haven't been able to get good oblique results, although I haven't placed too much emphisis on that yet.
Ziess' plan called for a dedicated illuminator cliped to the bottom of the condenser unit. Their plan uses both UV filters and frosted glass to deal with UV and a harsh bulb filiment. My design uses my microscope's Kohler (SP I am sure...) illumination, so I didn't need to add these elements to my design...
V 4.0 is coming along well. It is much thinner than 3.0, so it fits under the stage better. Now, I have to make the axial iris blades (16 of them! 4mm long, and 1mm wide... thank god I have a stereo microscope to cut them out) It will take a couple of days to get everything up and running...