title: iOS camera: manual exposure duration but auto ISO?
body: <p>I'm using the camera video feed for some image processing and would like to optimise for fastest shutter speed. I know you can manually set exposure duration and ISO using</p>
  
  <pre><code>setExposureModeCustomWithDuration:ISO:completionHandler:
  </code></pre>
  
  <p>but this requires one to set both the values by hand. Is there a method or clever trick to allow you to set the exposure duraction manually but have the ISO handle itself to try to correctly expose the image?</p>