How do I zoom periscope?

[Darren J.]

I'm losing it in my old age, I can't remember how I did it before and I can't find any documentation. I want to zoom my attack periscope from 1.5 to the higher power. Is it a specific key or a mouse click?

[GibsonSG]

"Tab" button

[bigboywooly]

Or roll the centre wheel on mouse forward