锁定3张连续照片的曝光

Question

是否有办法以10秒的间隔锁定3张连续照片的曝光，以便在此过程中光线不会改变？ （定时器）

do {
     try self.currentCaptureDevice.lockForConfiguration()
         if self.currentCaptureDevice.exposurePointOfInterestSupported {
             self.currentCaptureDevice.exposurePointOfInterest = CGPoint(x: 0.0, y: 1.0)
             self.currentCaptureDevice.exposureMode = .Locked
         }
      self.currentCaptureDevice.unlockForConfiguration()            
}
catch let error as NSError {
     print(error)
}

我注意到第一张照片后曝光被恢复为默认值。