Camera 2 fla sh не работает на некоторых устройствах. Реализация кода для fla sh:
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_MODE,CameraMetadata.CONTROL_AE_MODE_ON_ALWAYS_FLASH);
mPreviewRequestBuilder.set(CaptureRequest.FLASH_MODE, CameraMetadata.FLASH_MODE_TORCH);
mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AWB_MODE, CaptureRequest.CONTROL_AWB_MODE_FLUORESCENT);