Hello, I am working on a fairly complex iPhone app that controls the front built-in wide angle camera. I need to take and display a sequence of photos that cover the whole range of focus value available. Here is how I do it : call setExposureModeCustom to set the first lens position wait for the completionHandler to be called back capture a photo do it again for the next lens position. etc. This works fine, but it takes longer than I expected for the completionHandler to be called back. From what I've seen, the delay scales with the exposure duration. When I set the exposure duration to the max value: on the iPhone 14 Pro, it takes about 3 seconds (3 times the max exposure) on the iPhone 8 1.3s (4 times the max exposure). I was expecting a delay of two times the exposure duration: take a photo, throw one away while changing lens position, take the next photo, etc. but this takes more than that. I also tried the same thing with changing the ISO instead of the focus position and I get the same kind of delays. Also, I do not think the problem is linked to the way I process the images because I get the same delay even if I do nothing with the output. Is there something I could do to make things go faster for this use-case ? Any input would be appreciated, Thanks I created a minimal testing app to reproduce the issue : import Foundation import AVFoundation class Main:NSObject, AVCaptureVideoDataOutputSampleBufferDelegate { let dispatchQueue = DispatchQueue(label:"VideoQueue", qos: .userInitiated) let session:AVCaptureSession let videoDevice:AVCaptureDevice var focus:Float = 0 override init(){ session = AVCaptureSession() session.beginConfiguration() session.sessionPreset = .photo videoDevice = AVCaptureDevice.default(.builtInWideAngleCamera, for: .video, position: .back)! super.init() let videoDeviceInput = try! AVCaptureDeviceInput(device: videoDevice) session.addInput(videoDeviceInput) let videoDataOutput = AVCaptureVideoDataOutput() if session.canAddOutput(videoDataOutput) { session.addOutput(videoDataOutput) videoDataOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32BGRA ] videoDataOutput.setSampleBufferDelegate(self, queue: dispatchQueue) } session.commitConfiguration() dispatchQueue.async { self.startSession() } } func startSession(){ session.startRunning() //lock max exposure duration try! videoDevice.lockForConfiguration() let exposure = videoDevice.activeFormat.maxExposureDuration.seconds * 0.5 print("set max exposure", exposure) videoDevice.setExposureModeCustom(duration: CMTime(seconds: exposure, preferredTimescale: 1000), iso: videoDevice.activeFormat.minISO){ time in print("did set max exposure") self.changeFocus() } videoDevice.unlockForConfiguration() } func changeFocus(){ let date = Date.now print("set focus", focus) try! videoDevice.lockForConfiguration() videoDevice.setFocusModeLocked(lensPosition: focus){ time in let dt = abs(date.timeIntervalSinceNow) print("did set focus - took:", dt, "frames:", dt/self.videoDevice.exposureDuration.seconds) self.next() } videoDevice.unlockForConfiguration() } func next(){ focus += 0.02 if focus > 1 { print("done") return } changeFocus() } func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection){ print("did receive video frame") } }