title: Three.js camera rotation is weird
body: <p>I've just started with Three.js. Like really just now.</p>
  
  <p>After playing with it for an hour or so and building a tool that helps me understand how the different elements work together (Camera, Light, Objects), I found something strange.</p>
  
  <p>The tool: <a href="http://hotblocks.nl/tests/three/cubes.html" rel="nofollow">http://hotblocks.nl/tests/three/cubes.html</a></p>
  
  <p>This is the current default set up:</p>
  
  <ul>
  <li>the Camera is positioned 210 upwards and</li>
  <li>500 backwards and</li>
  <li>246 to the right</li>
  <li>the Camera is rotated slightly to the left</li>
  <li>the light is directly above and shines in all directions</li>
  </ul>
  
  <p>As you can see, the objects are at the very bottom of the viewport. So I want to turn the Camera downward, so I can see more of them.</p>
  
  <p>Try that: turn <code>camera.rotation.x</code> down.</p>
  
  <p>That works, but the angle of rotation is wrong! Instead of the Camera rotating, it's the World rotating around its Z axis.</p>
  
  <p>That's not right, is it?</p>
  
  <p>The Y axis is also wrong. It rotates the World around its Y axis.</p>
  
  <p>Rotating the Camera around its Z axis, works perfectly: the Camera rotates, not the World.</p>
  
  <p>Am I doing it wrong? Or understanding it wrong?</p>
  
  <p><strong>PS</strong> Since the Camera rotation is only around its Y axis, the objects' vertical edges should be vertical in the result as well. In the default set up, they are. Rotating the camera around its X axis, shouldn't change that, but it does. Only rotating around its Z axis should change that (and it does). Am I wrong?</p>
  
  <p><strong>PPS</strong> I know about <code>Camera.lookAt( THREE.Vector3 target )</code>, but that changes the rotation of the camera, including its Z axis, and that shouldn't be necessary, logically.</p>