SMZ-U why multiple ports?

[SanFran77]

My SMZ-U has a back port and a side-port. What is the function to have two? And why does the back one have a lens but the side-port doesn’t? Is it so that both have infinite focus despite having different lengths?

[PeteM]

Nikon offers a few different options, ranging from no camera port on the basic stand, to a single trinocular head, to teaching intermediates, and a dual port version as you apparently have.

It would be useful if you wanted to connect a still camera and a movie camera at the same time. For surgical stereo microscopes (not the SMZ-U, but others similar), extra ports are commonly used for an extra observer.

Depending on what's attached to the side port, a relay lens might be added.

[Scarodactyl]

Back in the day film type was a major consideration as well. Having two cameras would allow you to have multiple options on that front.
Having access to the infinity image on the aide port allows for adapters using shorter or longer tube lenses rather than a tube lens plus a reducing or expanding lens. I don't know if they actually made those though.

[Topcode]

My SMZ-U has a back port and a side-port. What is the function to have two? And why does the back one have a lens but the side-port doesn’t? Is it so that both have infinite focus despite having different lengths?

one port is the left view, other is the right view. In a stereoscope these are two different viewpoints, through two physically differently located lenses(which you can see by removing the front objective), so its important if not crucial to have a port for both. Have no idea why the side port has no tube lens though.