I'm puzzled why my ojects disappear whenever I press "0" key to preview camera angle. I've set my camera to 50mm and LOCK CAMERA TO VIEW. Cannot figure it out. They all disappear when I zoom out. 

By the way, I have set my unit of measurement to IMPERIAL. Is this a problem?

[![enter image description here][1]][1]
[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/ToTs8.png
  [2]: https://i.sstatic.net/dXbCW.png