Zoom in and Zoom out on Camera View Using Objective-C?

How to Apply Zoom in and Zoom out On Camera view Using UIPinchGestureRecognizer and AVCaptureDevice. It is Not Zooming properly.
Zoom Out is Not Working in My below Code :

 AVCaptureDevice *device =[AVCaptureDevice defaultDeviceWithMediaType:
                                                       AVMediaTypeVideo];
 AVCaptureDeviceFormat *format = device.activeFormat;
 CGFloat maxZoomFactor = format.videoMaxZoomFactor;
 const CGFloat pinchVelocityDividerFactor = 2.0f;

 if (pinchRecognizer.state == UIGestureRecognizerStateChanged || pinchRecognizer.state ==UIGestureRecognizerStateBegan)
 {
     NSError *error = nil;
      if ([device lockForConfiguration:&error])
      {
         CGFloat desiredZoomFactor = device.videoZoomFactor +
             atan2f(pinchRecognizer.velocity, pinchVelocityDividerFactor);

          // Check if desiredZoomFactor fits required range from 1.0
                                   //to activeFormat.videoMaxZoomFactor
          if((1.0 <= pinchRecognizer.scale) && (2.5 >= pinchRecognizer.scale))
          device.videoZoomFactor = pinchRecognizer.scale * pinchRecognizer.scale;  

        [device unlockForConfiguration];
      }
      else
      {
        NSLog(@"error: %@", error);
      }
 }  
}

Please help anyone.
Thanks