I had also seen those images and just had a closer look at them. On the back of the lens is a brighter one and a fainter one and the look like a filament as you say. They are perfectly aligned vertically, like I aligned them on the back of a chair with the lamphouse away from the microscope and the barely touch each other. Only thing I don't understand is why I cannot get them centered in the field lens without rotating the frosted lens a little. Maybe the lens should not be rotatable at all but should only be able to move back and force while being rock steady in other directions. I don't know.
If the light point source moves when rotate the frosted lens in the condenser then I guess one explanation is that the frosted lens may be misaligned within it's housing.
I decided to try and check for other forms of misalignment on mine and notices that the swing out field lens is out of alignment. It lands slightly tilted so it's not orthogonal to the light source.
To see what's up, I've turned the microscope on it's back, and there is a gap in the bottom casting where you can see what's going on. The lens doesn't land straight when it's tilted into position.
There is a wedge which acts as a stop - you can see it move then you tilt the lens back and forth with the scope on it's back.
This wedge has a black flat headed screw to the side, which controls where the lens lands when in position. I think this might be the adjustment screw for the lens position. Unfortunately mine is screwed all the way in, so there is no more adjustment to be had. The wedge has what looks like a rolled steel pin through it which is connected to the lens tilt mechanism. I suppose it must be spring loaded somewhere in there. I will try upload an image from my phone but it takes big images so I need to reduce them somehow...
If I can't adjust it the proper way, then, seeing I don't want to disturb the field diaphragm housing and all, I would prefer to add a shim to the wedge to try get it closer to alignment. I have some old feeler gauges I can cut worst case.
The whole block which houses the swing out lens and diaphragm and I guess a diagonal mirror, does look like it can be removed. I'm not sure if it can be put repeatedly back though and assembly was probably done with a jig or something.
I suspect that, unless you get the field lens aligned with the condenser, and all the rest behind it from the lamphouse, I guess you aren't going to get perfect Kohler illumination. What effects on resolution this may have I don't know but is the condenser is achromatic I imagine that would also affect things.
Does anyone have a service manual for the Orthoplan? That would help. I don't want to disturb too much on this scope...