Creating a video capture filter with DirectShow

program.cs

if (new FilterGraph() is IFilterGraph2 graphBuilder)
{
    // Create a video capture filter for the device
    graphBuilder.AddSourceFilterForMoniker(dev.Mon, null, dev.Name, out IBaseFilter capFilter);

    // Cast that filter to IAMCameraControl from the DirectShowLib
    IAMCameraControl _camera = capFilter as IAMCameraControl;

    // Get the current focus settings from the webcam
    _camera.Get(CameraControlProperty.Focus, out int v, out CameraControlFlags f);

    // If the camera was not in manual focus mode, lock it into manual at the current focus setting
    if (f != CameraControlFlags.Manual)
    {
        _camera.Set(CameraControlProperty.Focus, v, CameraControlFlags.Manual);
    }
}