Does Anybody Recognize this Inverted 'Scope?

[apochronaut]

Your iris has to be a condenser iris, so no field iris but I suspect that those rings are the field apertures for the two higher objectives, essentially preset field apertures, instead of an adjustable one. The only value of the field iris in establishing Köhler is that it gives you something to focus on and a centering device. Other than that it is an adjustable hole sizeable for each objective to optimize contrast. The two rings probably do the same thing preferentially. Can you then use their edges partially off axis to focus the condenser on to get Köhler because they must be at the field lens focal plane, I would think.
I am unsure if you have put a sample on the stage yet. If you put a prepared slide on the stage coverslip up, that would give you the working distance of about 1mm . Can you set it so you can see the centered filament, then defocus the filament by manipulating the condenser as above?

[GerryR]

The rings are just painted grooves around the post that holds the condenser. When the objective with the yellow marker ring is used, I merely slide the condenser assembly to the position of the yellow ring on the post; same for the objective with the green marker ring. I move the condenser assembly to the position of the green ring on the post.
When I put a specimen on the stage, I can focus on the specimen and the filament defocuses, mostly; I can still see a very blurred filament. I will try moving the condenser to get rid of it completely. Thanks for all your help.

[apochronaut]

Is there anywhere that looks like a location that might have housed a ground glass filter? Maybe got damaged or thought to be precious, like the missing sliders.

[GerryR]

Is there anywhere that looks like a location that might have housed a ground glass filter? Maybe got damaged or thought to be precious, like the missing sliders.

Not that I can see. The condenser assembly was intact and in pretty nice shape when I received it. I believe that once I get the specimen in focus, the filament defocuses; I just need to get everything set up properly. There is a filter slot just above the iris and below the bulb that I can slip a piece of ground glass into; I have some from when I repaired a camera, so I can cut a piece to fit.