Using tablet/smartphone as external dslr monitor I know there are apps like DslrDashboard and more but I would like to just get a real time monitor for my Nikon D5100. How is that possible?`
Of course connected wiyh a Hdmi-cable.
You can't do that. There is no tablet on the market (right now) that offers an HDMI input or any other physical display input. Your only option would be to stream compressed video over the USB (or Lightning on iPads) connection or Wifi to an app that displays that stream.