I'm trying to understand how to use the AVCaptureDevice.activeMaxExposureDuration option. From the description, it seems helping to instruct the auto-exposure algorithm to use the specified (maximum) exposure duration. In practice, it seems doest nothing. I tried to set the activeMaxExposureDuration to the activeFormat.maxExposureDuration value, but all captured photos have the lowest exposure duration equal to AVCaptureDevice.activeVideoMaxFrameDuration. Settings both, AVCaptureDevice.activeVideoMaxFrameDuration and AVCaptureDevice.activeMaxExposureDuration does the trick, but the viewfinder become terribly slow in low light. How does the standard camera archives higher exposure duration, while keeping the viewfinder responsive?