That tweet (and the accompanying photo) is basically an official announcement that at least part of STAR WARS: EPISODE VII is being shot with IMAX cameras.
We knew that the film would be being released in the format, and there were rumblings that J.J. was looking into using the cameras for the shoot, but this is the first real confirmation that they're indeed shooting native IMAX for some scenes.
Abrams used IMAX extensively on STAR TREK INTO DARKNESS, so he's no stranger to the equipment, and SW is arguably more acquitted to the format than even his popcorned-up TREK flicks. It'll be great to see the Millenium Falcon and the deserts of Tatooine blasted on a massive screen with the clarity those IMAX cameras provide.
I wouldn't expect that they just broke out the cameras for some location desert shooting, so keep your ears open for just how much of this bad boy is actually going to be embiggened to IMAX size for our enjoyment.
STAR WARS: EPISODE VII will be bigger and louder than Lucas ever got on December 18th, 2015.