title: camera digital zoom in ios 4.0 and later
body: <p>how can I implement a digital zoom slider for the camera.
  I use the following APIs: AVCaptureVideoPreviewLayer, AVCaptureSession, AVCaptureVideoDataOutput, AVCaptureDeviceInput.</p>
  
  <p>I would like to have the same slider, which is available in iphone 4 camera app.</p>
  
  <p>Thanks in advance for any tips and examples!</p>