Porthole Designs

[Konrad Schiecke]

I am completing restoration on my first porthole set,a 7" Tele-Tone. I assume that the vertical does not fill the screen and is only scanned vertically to maintain the transmitted aspect ratio of 1:33 to 1,correct?. The porthole opening was only a cosmetic issue with manufacturers except for Zenith which allowed the vertical to be scanned to the top and bottom with the push of the button, correct?
Appreciate any comments from porthole tv collectors.
Konrad