I'm in the process of building some custom optics for my Microstar IV and I've been going through old Reichert and Cambridge patents to understand the intent of the original illuminating optics. However, a problem I've run into is that few of their patents actually seem to work. As a simple example, this patent seems to closely match the diascopic illuminator in my Microstar IV (the actual spacing/sizes are different in the real thing of course, but the same lens elements in the same arrangement are present), so this is a fairly simple system that is known to work.
However, when I take their suggested spacings/lens radii (from Table II) and plug them into spectral simulation software, I get an image like this:
![Image](https://benedikt-bitterli.me/micro/HRzow2e.png)
The beam emerges roughly collimated out of the first lens group as it should, but the focal point of the second lens falls short of the suggested condenser aperture F2 (marked by the white line on the right in the image). Doing the math by hand, the focal length of lens group II should be around 90mm, but they suggest the distance to the condenser to be 123mm instead, which is quite a bit beyond the focal point (as in the simulation). In other words, the filament is not actually imaged at the condenser pupil.
I'm not too used to reading optical patents, so I could use the help of someone more familiar in these matters: Is it to be expected that parameters listed in a patent don't lead to a working implementation (to keep the "secret sauce" away from the public), or am I completely misunderstanding how a microscope illuminator is supposed to work?