How do push/pull zooms actually work

[ChrisP]

I've been playing with an old Pentax Push/Pull zoom and it got me wondering how it actually works. You have a metal sleeve over a metal barrel and when you move the sleeve forward and backwards the lens zooms, when you rotate the sleeve you focus. So I assume you're moving elements inside the lens. But how does this actually move them?

Is there an open space in the lens barrel that allows the elements to be connected to the sleeve? It seems like would require alot of open space because when the sleeve rotates for focusing it can rotate a long way and it can push/pull pretty far forward and back.

Next thing that came to mind would be magnets or something similar but I feel like that would move around too much. It doesn't feel like there's gears or anything...

If anyone could explain this or maybe show a diagram/cut-away of how this works I would greatly appreciate this. Right now I'm guessing they just douse the lens in unicorn blood and that provides the magic necessary to make things work.

Thanks in advance,

 

[Greyscale]

Think of it like a normal lens, with an internal helical for focusing like any normal lens, mounted on a sleeve over a long extension tube, with a rear element sometimes (but not always) at the back of the extension tube.

I had a Yashinon-R 90~190mm push-pull that was exactly that, a 90mm normal lens that slid up or down on a long extension tube, with no glass element at all in the tube. You could even separate the lens from the tube for storage or shipping.