title: What's the difference between setting the zPosition of a layer vs changing it via CATransform3DTranslate
body: <p>I have a layer where I am modofying its m34 transform property to get perspective. 
  I would have expected that by changing the zPosition, the size will change (as it appears further away) however when I set the zPosition property, the size does not change, but it does   when I use CATransform3DTranslate.</p>
  
  <p>Why is this? What's the difference between the following:</p>
  
  <pre><code>CATransform3D transform = CATransform3DIdentity;
  transform.m34 = 1.0 / -4000;
  myLayer.transform = transform;
  myLayer.zPosition = -500;
  </code></pre>
  
  <p>and</p>
  
  <pre><code>CATransform3D transform = CATransform3DIdentity;
  transform.m34 = 1.0 / -4000;
  transform = CATransform3DTranslate(transform, 0, 0, -500);
  myLayer.transform = transform;
  </code></pre>
  
  <p>The latter works how I expect, but I want to understand why the first does not.</p>